Abstract
Background
People with high-frequency episodic migraine or chronic migraine may have resistant or refractory forms. The lack of efficacy of pharmacologic therapies is a major clinical challenge that requires alternative strategies, including neuromodulation and exploration of new targets to improve disease management. The present study aimed to test the effectiveness of an accelerated protocol of theta burst stimulation (iTBS) via the dorso lateral prefrontal cortex (DLPFC) in a group of chronic migraine individuals who did not respond to monoclonal antibodies against calcitonin gene-related peptide (CGRP). The co-primary outcomes were the reduction in monthly headache frequency, use of symptomatic medication and perceived pain intensity. In parallel we wanted to understand the possible role of the prefrontal cortex in the emotional and cognitive functions likely responsible for treatment failure and to offer a possible non-pharmacologic option to individuals with difficult-to-treat migraine. To this end, we measured clinical outcomes along with an electroencephalogram (EEG) and behavioral responses to cognitive and emotional tests related to prefrontal functions.
Methods
This study was conducted in a controlled, single-blind design in 12 people with chronic refractory migraine. An accelerated protocol of iTBS on DLPFC was preceded by a sham session and followed by a two-month follow-up. Clinical data were collected and a neuropsychological assessment including anxiety, depression and cognitive profile was performed. Cognitive and emotional Stroop testing was performed at baseline, after sham and real stimulation, and at follow-up during high-density EEG recording to obtain event-related potentials (N2, N400 and late sustained potential (LP)). Stroop data from an age- and sex-matched control group were compared with those of migraine individuals.
Results
Monthly headache days, monthly medication days and headache intensity improved after real stimulation. A similar trend emerged for anxiety, depression, and cognitive performance. The Stroop test was impaired in the baseline, as evidenced by an increase in reaction time and a decrease in N2 and LP in the cognitive task, which returned to normal after real iTBS and at follow-up.
Conclusions
The results support the efficacy of iTBS as a non-invasive neuromodulation approach for the treatment of chronic, refractory migraine. They tentatively point to the role of cognitive fog and psychopathological symptoms in refractoriness to anti-CGRP drugs, which should be confirmed in larger multicenter studies, and suggest this non-pharmacological approach as another promising therapeutic option for people with difficult-to-treat migraine.
This is a visual representation of the abstract.
Keywords
Introduction
Chronic migraine is a disabling disorder, characterized by increased phenomena of central sensitization and dysfunction in the prefrontal cortex, thalamus, hypothalamus and trigeminal-cervical nucleus, which contribute to the persistence of pain (1,2).
In addition to a disturbance of pain modulation, chronic migraine is strongly associated with mood disorders, especially anxiety and depression, which significantly impair the patient's quality of life (3,4). In particular, individuals with chronic migraine often have difficulties with memory, attention and speed of information processing, suggesting that persistent pain signals may impair cognitive processes (5).
In recent years, the role of a neuropeptide called calcitonin gene-related peptide (CGRP) has emerged as a primary target to prevent activation of the trigemino-vascular system and the development of sterile inflammation, headache and peripheral and central sensitization phenomena (6). Monoclonal antibodies targeting CGRP or its receptors have been introduced as preventive migraine therapies for five years, with optimal results in terms of efficacy, tolerability and safety (7).
However, monoclonal antibodies against CGRP are large molecules that act in the periphery (6). According to this view, the effective inhibition of pain transmission at the trigeminal afferents could reduce headache intensity and prevent central sensitization, whereas the possible causes for the lack of response in chronic migraine are still controversial (8), with depression being one of the possible factors for refractoriness (9).
People with high-frequency episodic migraine (EM) or chronic migraine (CM) may have resistant or refractory migraine (10,11). Resistant migraine is defined as having failed at least three classes of migraine medications and suffering at least eight days per month of debilitating headache that has not improved for at least three consecutive months. Refractory migraine is defined as a migraine that fails to respond to all available preventive medications and suffers from debilitating headaches for at least eight days per month for at least six consecutive months (10,11). This form of migraine is characterized by resistance to current pharmacological treatments, including beta-blockers, anticonvulsants and monoclonal antibodies against CGRP (9). In addition, trigeminal hypersensitivity and alterations in pain processing networks have been identified as possible factors contributing to treatment resistance (11). The lack of efficacy of pharmacologic therapies for chronic migraine is a major clinical challenge that requires alternative strategies, including neuromodulation and the exploration of new pharmacologic targets to improve disease management (12).
Among neuromodulation techniques, repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex (DLPFC) has been shown to be a promising non-invasive approach to pain modulation in chronic migraine. A recent systematic review and meta-analysis examined how rTMS via the DLPFC can significantly reduce migraine frequency and pain intensity, with clinical benefits lasting up to six weeks after treatment (13). These effects appear to be independent of the intensity of stimulation and the number of pulses delivered, suggesting a stable and reproducible mechanism of action (13,14). A recent review also highlighted the efficacy of accelerated protocols of rTMS via the DLPFC with alternative stimulation modalities to the more commonly used high frequencies, such as theta burst stimulation, in the treatment of depression, which is one of the factors facilitating refractoriness (15).
The present study aimed to test the effectiveness of an accelerated protocol of theta burst stimulation via the DLPFC in a group of chronic migraine individuals who did not respond to monoclonal antibodies against CGRP. We wanted to understand the possible role of the prefrontal cortex in the emotional and cognitive functions that are likely responsible for treatment failure, as well as to offer a possible non-pharmacological option. To this end, we measured changes in headache frequency, symptomatic medication use and headache intensity in the baseline and after sham stimulation compared to real stimulation as the primary endpoint. We also examined the trend of change in disability scores, anxiety and depression scales, and cognitive performance induced by real stimulation compared to the sham and baseline conditions. Cognitive and emotional electroencephalogram (EEG) correlates were used to test changes in prefrontal cortical regions.
Methods
Subjects
Inclusion criteria were a diagnosis of chronic migraine, fulfilment of the criteria for reimbursement of anti-CGRP monoclonal antibodies, according to Italian Health Minister: a frequency of at least eight days with migraine per month, unresponsive to antidepressants, antiepileptics and beta-blockers, and the absence of cardiovascular and cerebrovascular ischemic pathologies. Thus, we included individuals with migraine who had been treated with anti-CGRP drugs for at least six months and who had no or only a slight decrease in headache frequency in the last three months (less than 50% decrease). In addition, participants had to be able to give informed consent in accordance with local ethical regulations. Exclusion criteria were concomitant antidepressant therapy, a current or previous diagnosis of epilepsy, a concomitant psychiatric disorder according to Diagnostic and Statistical Manual of Mental Disorders, 5th edition criteria with respect to anamnestic findings (with the exception of anxiety and depressive symptoms), or the presence of implanted electronic devices that could interfere with neurostimulation. The study was approved by the Ethics Committee of the General Hospital of Bari Policlinico and each participant signed an informed consent form.
Participants were recruited between August 2023 and August 2024, with the last evaluation in December 2024. Recruitment took place during routine neurological visits and was conducted directly by the treating neurologist. Eligibility was assessed through clinical interview and neurological evaluation, with confirmation through medical records. No formal age criterion was applied, although all included participants were adults between 18 and 65 years of age. In the recruitment phase, 35 of the 212 patients treated with monoclonal CGRP antibodies had refractory migraine, whereas 25 met the inclusion criteria because eight patients had a concomitant psychiatric diagnosis with antidepressant medication, one patient had a comorbidity with epilepsy and one patient had an implanted electronic device. Among the 25 participants proposed for the protocol, only 12 participants took part in the study, which was conducted at the Department of Neurophysiopathology of the General Hospital of Bari Policlinico in Italy. The reasons for non-participation included logistical and time-related difficulties in following the experimental protocol, as well as an aversion to the neuromodulation procedure.
Study design
In this study, the effects of accelerated protocol of intermittent theta burst stimulation (iTBS) on clinical symptoms, cognitive and emotional traits assessed with behavioral responses and EEG potentials related to specific tests for prefrontal functions were investigated in a one-group, one-blind design. The protocol consisted of two successive phases: an initial sham stimulation phase, followed by a real stimulation phase after a four-week interval (Figure 1).
Diagram of the experimental protocol with timing and evaluations at different time points.
The sham stimulation preceded the real stimulation in every case because the after-effect of TMS stimulation is of an individually unpredictable duration.
At the beginning of the study (T0), the participants underwent an initial examination in which the motor resting threshold and the exact localization of the left DLPFC were determined using the NetBrain Neuronavigator system (EB Neuro, Firenze, Italy). Due to the use of a circular coil, which has a lower localization accuracy compared to other types of coils, neuronavigation was repeated before the start of each daily stimulation session. The sham stimulation phase was performed, followed by a re-examination at T1, four weeks after the intervention. The actual stimulation phase then began and participants were reassessed at T2, four weeks after completion of active treatment. The final follow-up examination (T3) took place eight weeks after T2, so that the observation period after the real stimulation was 12 weeks in total (Figure 1).
Clinical and neuropsychological assessment
At each evaluation time point (T0, T1, T2 and T3), participants underwent a comprehensive battery of clinical, psychological and neurocognitive assessments to monitor symptom development and treatment effects. The assessments included evaluations of migraine features, depressive and anxiety symptoms, apathy, pain intensity, fatigue, sleep disturbances, allodynia and overall quality of life.
Participants underwent the clinical assessment that we described in previous studies (16). They were requested to fill a standardized headache diary (16), throughout the entire treatment and follow-up period, recording each headache episode as it occurred. This is a recording method routinely used in clinical practice. The diary includes the allodynia scale with scores from 0 to 12, according to previous studies (17). Monthly headache days (MHDs) was documented by recording the number of headache days per month, along with the monthly medication days (MMDs) and intensity of headache using a Numerical Rating Scale (NRS) from 0 = no pain to 10 = maximal tolerable headache. The Migraine Disability Assessment Score Questionnaire (MIDAS) (18) was also used. The MIDAS questionnaire, which was validated for a three-month recall period, was completed at T0, T1, T2 and T3 in relation to the last three months but was not included as part of the primary outcome, as the time after the sham or real intervention should only partially influence the overall score. For the mood assessment, the Beck Depression Inventory-II (BDI-II) (19), Beck Anxiety Inventory (BAI) (20), Hamilton Depression Rating Scale (HDRS) (21) and Starkstein Apathy Scale (SAS-I) (22) were administered at each time point.
Additionally, neuropsychological performance was assessed using the Trail Making Test A & B (TMT A & B) (23), Digit Span Backward (24), Symbol Digit Modalities Test (25) and Phonemic and Semantic Verbal Fluency Test (26).
Neurophysiological assessment
To explore neurophysiological correlates of cognitive and emotional processing, EEG recordings were performed during computerized Stroop Test and Emotional Stroop Test tasks.
Stroop task: Cognitive session
The stimuli were displayed individually on a monitor with a black background. During the test, a list of words (green, blue and red) was presented in a random order. However, the color of the words could match the presented word or not (e.g. the word “blue” in blue ink or the word “blue” in green ink). Subjects were then asked to consider the color of the ink and ignore the semantic meaning of the word (e.g. answer “green” instead of “blue” as in the previous example) by quickly pressing the space bar. A total of 60 stimuli were administered, which were displayed on the screen for two seconds, each five seconds apart. The stimuli consisted of the words “blue”, “red” and “green” and were presented in randomized order as follows: 10 congruent “blue” (the word “blue” was colored blue); 10 congruent “red”; 10 congruent “green”; 10 incongruent “blue” (five colored red and five colored green); 10 incongruent “red” (five colored blue and five colored green); and 10 incongruent “green” (five colored red and five colored blue) (27). Correct (c), wrong (w) and missing (m) responses were considered.
Stroop task: Emotional session
A series of words in Italian, selected for their potential to attract attention and characterized by different emotional valences (positive, negative, neutral), were shown in random order. The words were presented in one of four different colors: green, blue, red and yellow. Participants were asked to recognize only the color of the text and to ignore the meaning of the word and respond as quickly as possible by pressing the corresponding key on a keyboard with four colored keys (green, blue, red and yellow). A total of 48 stimuli were presented, each of which was displayed for two seconds, with an eight-second interval between one presentation and the next.
The stimuli included 16 words with positive valence, 16 words with negative valence and 16 words with a neutral value. The four presentation colors (green, red, blue and yellow) were used in a counterbalanced distribution, with each color appearing 12 times at random (28). Correct (c), wrong (w) and missing (m) responses were considered.
To assess the baseline performance of migraine individuals, we compared event-related potential (ERP) responses at T0 with those of a group of 12 age- and sex-matched healthy control subjects (three men, mean ± SD age: 49.9 ± 10.1 years). Control participants were recruited through internal advertisements within our institution (including hospital staff and their acquaintances) and were selected after a clinical interview confirmed the absence of primary headache disorders and other neurological or general medical conditions.
iTBS stimulation protocol
The stimulation was performed with the STM9000 stimulator (EB Neuro), which is equipped with a 90-mm circular, air-cooled coil with integrated control and display. The treatment consisted of 20 iTBS sessions spread over four consecutive days, with five sessions per day, resulting in a total of 32,400 stimuli. Each session delivered 1620 pulses divided into 54 triplet bursts, with a train duration of two seconds and an interval of eight seconds between trains. Stimulation was administered at 110% of resting motor threshold, which was determined at the beginning of the study. To maintain procedural consistency and minimize potential fatigue effects, a 15-minute break was taken between sessions. During both the sham and real aiTBS treatment phases, participants were unaware of the stimulation condition to ensure blinding. The sham stimulation protocol was designed to replicate the acoustic and somatosensory effects of real stimulation at the same time as minimizing cortical activation. Specifically, the same number of stimuli was delivered at a frequency of 1 Hz with the coil tilted at 90°, with one wing touching the scalp, aiming to minimize cortical activation at the same time as maintaining the acoustic and somatosensory features of real stimulation, This approach, which includes auditory mimicry of the active protocol, has been used in previous sham-controlled rTMS studies as an effective method for participant blinding (29). This setup ensured that participants perceived a sensation comparable to real stimulation at the same time as limiting cortical effects, thereby enhancing the validity of the control condition.
EEG recording technique
Electroencephalographic (EEG) data were recorded using the Micromed Brain Quick system (Natus, Middleton, WI, USA), which has a high-density electrode cap configured according to the extended international 10-20 system (Fp1, Fpz, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, Oz, O2, AF7, AF3, AFz, AF4, AF8, F5, F1, F2, F6, FT7, FC5, FC3, FC1, FCz, FC2, FC4, FC6, FT8, C5, C1, C2, C6, TP7, CP5, CP3, CP1, CPz, CP2, CP4, CP6, TP8, P5, P1, P2, P6, PO7, PO3, POz, PO4 and PO8). The cap was equipped with 61 electrodes positioned to ensure comprehensive cortical coverage, including the frontal, central, parietal, occipital and temporal regions. A biauricular reference electrode was used and a ground electrode was placed on the right forearm to minimize external interference. Two additional electrodes were placed on the outer canthi of both eyes to detect artifacts due to eye movements. Impedance values were kept below 5 kΩ throughout to improve signal quality and reduce noise contamination. EEG signals were recorded at a sampling rate of 256 Hz using a 0.1–70-Hz bandpass filter and a 50-Hz notch filter to eliminate mains noise. Recordings were made while participants completed the computerized Stroop test and the emotional Stroop test so that neurophysiological responses to cognitive and emotional stimuli could be assessed.
EEG data analysis
EEG pre-processing
The EEG data were processed using an automated pipeline based on the EEGLAB, version 2022 (https://eeglab.org) software running on the MATLAB platform (MathWorks Inc., Natick, MA, USA). First, the signals were filtered with a finite impulse response filter between 1 and 30 Hz to remove low-frequency drifts and high-frequency noise. To correct the continuous data and eliminate artifacts, the ASR (i.e. artifact subspace reconstruction) method was applied, which allows the automatic removal of corrupted data segments and erroneous channels.
The channels with artifacts were then interpolated and all signals were referenced to the average reference. A threshold of 20 was set as the maximum allowable standard deviation for a 0.5-second window to ensure robust artifact suppression. In addition, channels that remained flat for more than five seconds, had a SD of high-frequency noise of less than 4, or had a correlation of more than 0.8 with neighboring channels were removed.
An independent component analysis was then performed, and the artifact components were identified and automatically rejected using the multiple artifact rejection algorithm. Components with a probability of being artifacts greater than 0.50 were removed. Finally, the data was epochalized from −0.3 to 2 s and a baseline correction was performed to normalize the signal.
EEG analysis
We considered the waves with the largest magnitude in the frontal regions.
The components most commonly used in clinical and experimental settings include N2 and N400, which reflect mechanisms related to conflict monitoring and automatic response inhibition, respectively, as well as processes of semantic integration and cognitive interference management. These components have been shown to exhibit increased sensitivity in detecting changes in frontocortical circuits, even in clinical populations without overt cognitive deficits (30). The Stroop task, in both its cognitive and emotional versions, has been shown to be a robust and extensively validated tool to elicit N2 and N400 components. This is a result of its ability to elicit a conflict between automatic and voluntary processes. This allows a targeted investigation of the neural mechanisms involved in response inhibition and cognitive interference management by analysing the associated ERP components (31).
For the analysis of the Stroop test, cognitive session, the data were divided into two conditions: congruent stimuli (e.g. the word “red” in red ink) and incongruent stimuli (e.g. the word “red” in green ink). The early negative response (N2) was tested as maximum negativity in the time interval 200–350 milliseconds, the N400 as a maximal negativity in the 350–500 millisecond time range and in the range of 600–1000 milliseconds for the late sustained potential (LP). In the emotional Stroop test, we considered the N2-wave detected in the frontal regions in the same time interval. Epochs were averaged for each condition in controls and migraine individuals at T0, T1, T2 and T3. For the cognitive Stroop task, 30 artifact-free epochs were averaged per condition (congruent and incongruent), whereas, for the emotional Stroop task, 16 epochs were averaged for each emotional valence (positive, negative and neutral).
Statistical analysis
To determine the minimum sample size required for the statistical analysis, we used G*Power software (http://www.gpower.hhu.de) taking into account a unique variable; namely, the number of headache days per month. The calculation was performed for a repeated measures analysis of variance (ANOVA) with a factor within subjects, with an expected average effect (f = 0.3), a type I error (α) of 0.05 and a desired power of 0.80. The number of measurements for each participant was set at four, whereas the correlation between repeated measures was set at 0.7 based on previous rTMS studies on chronic headache, which showed relative stability in repeated measurements over time (30). The analysis indicated that a sample of 12 participants would be sufficient to obtain an effective power of 0.83, thus guaranteeing an adequate probability of detecting real effects in the statistical model. This value was evaluated as suitable for the study's design because it balanced the necessity for adequate statistical power with the limitations inherent to participant recruitment.
As a primary endpoint, we considered three variables, such as monthly headache days, headache intensity and days of symptomatic medication use, which were introduced into the repeated measures ANOVA provided by the Jamovi software with a post-hoc Bonferroni test, corrected for multiple comparisons among the four times of evaluation for single variables. To assess the efficacy of the neurostimulation protocol, we expected no significant changes in the variables between the baseline condition (T0) and sham stimulation (T1) and a significant reduction in the variables considered between the baseline condition and post-neurostimulation times (T0 vs. T2 and T3). For the multiple tests with three variables, we considered p-values below 0.016.
Secondarily, we also considered the significant changes between the time after sham stimulation (T1) and the time after real stimulation (T2 and T3).
Because this was an exploratory pilot study, we looked at the trend of change between baseline (T0) and after real stimulation (T2 and T3) for the disability score (MIDAS) and allodynia, the depression and anxiety scores, and the cognitive tests, whereas we did not expect a significant change between baseline and post-sham stimulation times. Repeated measures ANOVA was also used, with the post-hoc Bonferroni test.
ERP data from the Stroop task were analyzed using non-parametric permutation-based t-tests, as implemented in the MATLAB toolbox Letswave 7 (https://letswave.cn). Comparisons across phases (T0, T1, T2 and T3) within the migraine group were performed using dependent-sample t-tests, whereas data from migraine individuals at T0 were compared to controls using independent-sample t-tests. The researchers who examined the data were blinded to the conditions.
Results
In total, 12 participants with chronic migraine who met the inclusion criteria were included in this study. The iTBS was well tolerated and no participant reported adverse reactions, apart from a persistent local burning sensation in one case and a mild painful contraction of the throat during one day in another case. Table 1 shows the key demographic and clinical characteristics, including gender, age, disease duration, and anti-CGRP therapy. The mean ± SD age of the sample was 51.42 ± 17.83 years and the participants had a disease duration of 33.88 ± 17.15 years. At the beginning of the study, the participants suffered from headaches on more than 15 days per month, with more than 10 days being treated with symptomatic medication (Table 2). All of them had acute allodynia. According to the Italian rules for reimbursement of drugs for CGRP, all participants had been previously treated with amitriptyline and topiramate, nine participants with beta-blockers, although this was not indicated in three cases due to hypotension and basal bradycardia. All individuals with migraine had also received at least three cycles of botulinum toxin A type. Anti-CGRP treatment was maintained unchanged throughout the entire study period, including both sham and real iTBS phases, as well as follow up.
Demographic and clinical characteristis of the sample.
Mean ± SD values of clinical, emotional and cognitive variables at four time points.
Note: MIDAS = Migraine Disability Assessment Score Questionnaire; MHDs = monthly headache days; MMDs = monthly medication days; NRS = Numeric Rating Scale; BDI = Beck Depression Inventory; BAI = Beck Anxiety Inventory; SAS-I = Starkstein Apathy Scale; FLUS = Semantic Verbal Fluency Test; FAS = Phonemic Verbal Fluency Test; TMT_A = Trail Making Test A; TMT_B = Trail Making Test B; HDRS = Hamilton Depression Rating Scale; SPAN_B = Digit Span Backward; SDMT = Symbol Digit Modalities Test; STROOP_RT = stroop reaction time; EMO_STROOP_RT = emotional stroop reaction time; STROOP_C = stroop correct answers; STROOP_W = stroop wrong answers; STROOP_M = stroop missing; EMO_STROOP_C = emotional stroop correct answers; EMO_STROOP_W = emotional stroop wrong answers; EMO_STROOP_M = emotional stroop missing.
Primary outcome
Headache frequency showed a trend towards improvement after true TMS (Table 2). The number of headache days decreased significantly, but the significance level was slightly above the threshold for multiple comparisons (repeated measures ANOVA, F = 3.91, p = 0.017, η²p = 0.262), as was the Bonferroni test between T0 and T2 (t = 3.44, p = 0.033) (Figure 2). Days of symptomatic medication use were significantly reduced (repeated measures ANOVA, F = 5.62, p = 0.003, η²p = 0.338). The Bonferroni test showed a significant change between T0 and T2 (t = 4.14, p = 0.010). Headache intensity improved significantly at T2 and T3 compared to T0 (repeated measures ANOVA, F = 5.56, p = 0.003, η²p = 0.336: Bonferroni test T0 vs. T2, t = 4.16, p = 0.009, T0 vs. T3, t = 4.70, p = 0.004). There was also a sham effect on headache intensity, but this was not significant (T0 vs. T1, t = 2.91, p = 0.084). We were unable to detect a change between T1 and T2 and T1 and T3 in any of the variables examined (Figure 2).
Mean ± SD values of headache frequency, expressed as number of days with headache in one month, and number of monthly days with symptomatic drugs use and headache intensity, expressed in terms of numerical rating scale (NRS) from 0 to 10, in the 12 migraine individuals at baseline (T0), after sham stimulation (T1), and after 1 month (T2) and 3 months (T3) after real stimulation
Other clinical variables
The MIDAS score showed a trend toward a global improvement, but we detected no change in the Bonferroni test (repeated measures ANOVA, F = 3.42, p = 0.029, η²p = 0.237). Also, the allodynia score showed similar trend (repeated measures ANOVA, F = 3.54, p = 0.025, η²p = 0.244).
Psychopathological and cognitive features
Although raw scores are reported, cognitive performance was assessed by normalizing the results according to the Italian validation criteria for each neuropsychological test. Specifically, raw scores were adjusted based on normative data stratified by age and education level, allowing for an accurate evaluation of each participant's cognitive functioning relative to the general population. This normalization process ensured that individual performances were interpreted in a standardized manner, accounting for demographic differences and reducing potential biases related to inter-individual variability.
The exploratory statistical analysis showed a trend through a significant effect of time on several cognitive-emotional variables. On the cognitive measures, the symbol digit modalities test improved (F = 4.03, p = 0.015, η²p = 0.268), with higher scores at T3 compared to T0 (t = −3.54, p = 0.028) and TMT-B (F = 7.43, p < 0.001, η²p = 0.403) with improvements at T3 compared to T0 (t = 3.53, p = 0.028) and T3 compared to T1 (t = 3.78, p = 0.018) . On the emotional side, anxiety (BAI) showed a further decrease from T2 to T3 (F = 6.16, p = 0.002, η²p = 0.359; t = 3.71, p = 0.021), whereas apathy (SAS-I) decreased significantly between T0 and T3 (F = 3.06, p = 0.042, η²p = 0.217; t = 3.34, p = 0.039) (Table 2).
ERP analysis
Cognitive stroop test
The reaction times to the cognitive Stroop tasks were significantly slower in individuals with migraine than in controls at T0, with a significant difference between the groups (controls (CT) = 843 milliseconds, T0 = 1387 milliseconds, t22 = −3.59, p = 0.002). However, at follow-up (T3), there was a significant improvement in performance among the individuals with migraine, and no substantial differences were observed between the groups (CT = 842.6 milliseconds, T3 = 962.6 milliseconds, t22 = −0.916, p = 0.370), indicating a possible return to normal performance levels.
The number of errors or omissions was also similar between individuals with migraine and controls at T0 and did not change over the course of the experiment or during follow-up.
For congruent stimuli, no relevant difference in latency for N2, N400 and LP was observed between groups. We observed that migraine individuals in the baseline condition (T0) showed a reduced amplitude of N2 and LP evoked by the congruent stimulus compared to controls (Figure 3a).
(a) Grand average of event related responses obtained with the congruous stimulus in migraine individuals at T0 and controls and in (b) in migraine individuals at T0, T1, T2 and T3. The N2 wave and the late positive (LP) appeared to be reduced in migraine individuals in basal conditions, but both recovered in T3.
The amplitude of the N2 component increased in phases T2 and T3 compared to T0. There was also a sham effect that did not lead to significant changes (Figure 3b). At T2 and T3, the N2 amplitude recovered compared to controls (Figure 3b). The LP showed a slight increase at T2, which became more pronounced during the follow-up examination. Figure 4 shows the maps of the statistically relevant results. The t-test maps, corrected with cluster-based permutation, are shown (Figure 4).
Topographical maps of grand average of main waves evoked during the stroop test in relation to the congruous and incongruous stimulus in controls and migraine individuals in the different conditions. Significant results of Student's t-test with multiple permutation correction are shown on the right.
For incongruent stimuli, the latencies of N2, N400 and LP were similar in individuals with migraine and controls and did not change in the different phases of the study.
Recognition of the incongruent stimulus elicited a clear N2 component and later a negative potential. The amplitude of the N2 component was reduced under baseline compared to controls (Figures 4 and 5a). It increased significantly after both sham and real stimulation at T1 and T2 and increased significantly at T3 compared to baseline (Figures 4 and 5b). The late potential was significantly reduced in migraine individuals compared to controls in the baseline (Figure 5a), but increased after real stimulation in the T2 and T3 conditions compared to the T0 condition (Figures 4 and 5b).
(a) Grand average of event related responses obtained with the incongruous stimulus in migraine individuals at T0 and controls and in (b) in migraine individuals at T0, T1, T2 and T3. The N2, N400 wave and the late positive (LP) appeared to be reduced in migraine individuals in the baseline, but the late LP recovered in T2 and T3.
Emotional stroop
Individuals with migraine showed slower reaction times than the control group at T0 (CT = 837 milliseconds, T0 = 1248 milliseconds, t22 = −3.37, p = 0.003). At follow-up, although the difference had reduced, it remained statistically significant (CT = 836.7 milliseconds, T3 = 1104.7 milliseconds, t22 = −2.305, p = 0.031), suggesting a partial but not complete recovery of performance in individuals with migraine.
The N2 appeared to be reduced in migraine individuals under basal conditions at T0 compared to control subjects (Figure 6a), although no statistical difference was observed. The iTBS, both in the sham and real modality, caused an increase in the amplitude of the N2 components (Figure 6b). However, there was no statistically significant result.
(a) Grand average of event related responses obtained with the negative words in migraine individuals at T0 and controls and in (b) in migraine individuals at T0, T1, T2 and T3. The P2, N2 and P300 showed changes in respect to controls, and during the T1, T2 and T3 session compared to T0. However, no statistical difference in the comparison between individuals with migraine at T0 and controls, and individuals with migraine in the different conditions were found.
Considering the words with positive contents, individuals with migraine at T0 showed reduced N2 amplitude in respect to controls (Figure 7a). There was an increase in amplitude of the N2 wave in T2 and less evidently in T1 and T3 (Figure 7b). No statistically relevant differences between individuals with migraine at T0 and controls and among migraine in the different conditions emerged.
(a) Grand average of event related responses obtained with the positive words in migraine individuals at T0 and controls and in (b) in migraine individuals at T0, T1, T2 and T3. The N2 appeared to be reduced at T0 in respect to controls, whereas, in the T3 session, the P2 appeared to increase in amplitude with respect to other conditions and the N2 in T2 and T3 with respect to T0 and T1.
Discussion
In the present study, we investigated for the first time the effects of an accelerated protocol of iTBS of the left DLPC in a cohort of chronic migraine individuals who showed refractoriness to preventive treatments, including monoclonal antibodies against CGRP. Individuals with migraine showed a good effect on the main features of headache. They also showed a trend toward an improvement in cognitive functions related to the prefrontal regions stimulated with iTBS. The ERP evoked with the cognitive and emotional Stroop test changed after iTBS and showed increased activity in the frontal regions.
Primary outcome
Chronic migraine individuals are a challenge for clinicians, although anti-CGRP treatment together with botulinum toxin is a reliable and effective option (32).
ITBS reduced the frequency of monthly headache days after the real treatment, whereas this positive effect was far from the target of a 50% reduction in headache frequency and was approximately 30% of the MHD, which is quite good in individuals with difficult-to-treat migraine. We observed an improvement in the use of rescue drugs and in headache intensity. Although the small number of participants did not allow significant results to be found in the post-hoc analysis between the sham and the real effect, with the exception of headache intensity, the sham effect was weak and the improvement at follow-up was stable, suggesting a long-lasting effect of iTBS.
High-frequency rTMS targeting the DLPFC has already been tested in individuals with chronic migraine (33). A recent meta-analysis confirmed its efficacy in reducing migraine symptoms; however, the findings were based on a pooled analysis of studies involving both episodic and chronic migraine patients (13).
The present study suggested the effectiveness of prefrontal cortex stimulation in refractory chronic migraine using an accelerated theta burst protocol. This temporally concentrated stimulation modality may offer advantages over conventional high-frequency rTMS protocols, including shorter treatment duration, greater tolerability and potentially more sustained neuroplastic effects.
Although neurophysiological studies have suggested that anti-CGRP monoclonal antibodies exert a central effect on migraine-related brain dysfunctions, possibly restoring cortical excitability through a strong antinociceptive mechanism (34,35), this effect alone may not be sufficient in patients with a long-standing history of migraine, comorbid anxiety or depression, and functional cognitive vulnerabilities, even when neuropsychological performance remains within the normal range.
Other clinical variables
Migraine-related disability measured by MIDAS decreased in line with global clinical improvement, although the short assessment interval would diminish the usefulness of this index.
The allodynia score also showed a similar tendency to decrease with true stimulation, which may be an important finding about the effects on central sensitisation phenomena that requires further confirmation.
Effects on anxiety and depression and cognitive tests
The selected individuals with migraine patients exhibited the characteristics of refractoriness, although the reasons for this are not entirely clear (8,9). Although there was no psychiatric diagnosis of major depression, the scales showed a trend through an improvement in depressive and anxiety symptoms over the course of the experiment, which needs to be confirmed with an enlargement of case series.
The accelerated protocol is recommended for psychiatric disorders with a specific indication for non-invasive neurostimulation, such as depression, due to its safety and validity in terms of treatment duration and total number of stimulation sessions (15).
In addition to the improvement in migraine, which was the primary outcome, we also observed a benefit on all cognitive tests that measure cortical frontal functions, including apathy, which was less pronounced at follow-up at T3.
Individuals with chronic migraine often show a subtle cognitive deficit (5,36). The tests that we performed for the main frontal functions were normal in relation to age and years of study, but they continued to improve over the course of the experiment and at follow-up, with a significant effect at T3 for the symbol digit and the trail making tests.
The small number of participants was not suitable for establishing a correlation between the clinical and neuropsychological changes. However, the trend toward the global improvement we observed suggests that high-frequency of migraine, anxiety, depression and brain fog may be closely linked in a self-perpetuating cycle. However, this hypothesis needs to be tested in larger groups of patients.
Stroop test and event-related potentials
The DLPFC plays a central role in mood control, pain modulation (13,15) and the cognitive functions of executive memory and attention (35).
We applied the Stroop test with stimuli with cognitive and emotional content, evaluating the behavioral response and the evoked responses, which are more represented in the frontal regions and modulated by iTBS. The Stroop test measures executive control functions, which appear to be impaired in chronic migraine individuals as they showed prolonged reaction times compared to control subjects.
The N2 component, which is mainly represented in the frontal regions, was also reduced in amplitude in individuals with migraine before the neuromodulation task. We did not focus on the later N400, which was not as clearly represented in the frontal regions or modulated by iTBS, although we also evaluated the latest negativity, which was also reduced in the basal condition compared to controls. The fronto-central N2 component is consistently found to reflect conflict monitoring processes or overcoming of inhibition, a cognitive process which could be sustained in time, generating the negative potential after 500 milliseconds (27). Moreover, the executive control capacity and its neural bases are of considerable plasticity, and the iTBS over the DLPFC improved the reaction times and increased the ERP amplitudes, with a weak sham effect. The waves that are easily recognizable and modulated by iTBS appear to originate from the middle frontal regions and in particular from the anterior cingulate cortex (27). The increasing effect we observed after DLPFC stimulation may indicate a contribution of these areas to the generation of such responses as well as a diffuse effect on other frontal areas.
The iTBS effect persisted over time because it was present at follow-up. Accordingly, the clinical improvement persisted, albeit in an attenuated form. In general, the duration of effect of iTBS is estimated to be around six weeks (37). The present results may suggest that the neurophysiological effects persist over time and may even intensify at follow-up, despite a concurrent reduction in clinical benefit. This could be an after-effect of the accelerated protocol, which concentrates several stimulation sessions in a short period of time, but needs to be confirmed in further studies. The emotional Stroop test showed the same trend as the cognitive Stroop test, but the higher variability of the responses may have been responsible for the lack of significance, which should be confirmed in larger series.
Limitations
This study should be considered a pilot study with regard to the cognitive and emotional outcomes, aimed at evaluating the potential benefits of accelerated iTBS in refractory migraine. The exploratory investigation of the emotional and cognitive aspects requires confirmation in larger samples. In general, the monocentric model of the study represents a major limitation for the final confirmation of the efficacy of neurostimulation.
Although iTBS has been welcomed by people with migraines because they resist even very specific migraine therapy, the protocol is time consuming, less suitable for workers and difficult for outpatients who live far from the hospital.
This study was conducted in a real-world clinical context and followed a single-blind, within-subject design. Although this approach does not reach the methodological stringency of a randomized double-blind trial, it was chosen to ensure that all participants could access the active treatment, as required by ethical guidelines. Specific procedures, such as coil tilting and acoustic simulation, were implemented to support participant masking. The success of blinding was not formally assessed, which could be viewed as a limitation. However, it is important to note that formal blinding assessment is reported in only a small proportion of rTMS trials and, even in those cases, full blinding is rarely achieved.
Conclusions
The results of the present study indicate the effectiveness of iTBS as a non-invasive neuromodulation strategy for the treatment of chronic migraine that does not respond to pharmacological treatment. The frequency of headaches tended to decrease after treatment, although not by more than 50%, but the intensity of the headaches and the use of acute treatments were reduced to a greater extent. At this moment, we cannot establish whether the beneficial effect on the cognitive and emotional tests was primarily induced by the DLPFC increasing activity, or whether it was connected to the general improvement of migraine and reduction of pain. In any case, the iTBS seemed able to influence the negative circuit of chronic pain, mood disorder and cognitive impairment, which cooperates in determining the clinical picture of chronic migraine individuals. Although cognitive abilities were in the normal range, the patients showed suboptimal performance at the beginning of the study. These results could indicate a mild functional cognitive inefficiency, also referred to as “cognitive fog” which in combination with mood changes could potentially contribute to reduced responsiveness to anti-CGRP monoclonal antibodies. Non-pharmacological strategies must also be considered as useful support in the era of anti-CGRP treatment, at least in more complex individuals. Multicenter trials, potentially using less expensive and easily disposable devices such as electrical stimulation, could improve the evidence for a reliable option for refractory migraine.
Chronic migraine refractory to monoclonal antibodies against CGRP showed global improvement under non-invasive stimulation of the dorsolateral prefrontal cortex. Non-pharmacological interventions on brain fog, anxiety and depression could be a therapeutic option for refractory chronic migraine.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work was supported by #NEXTGENERATIONEU (NGEU) and funded by the Ministry of University and Research (MUR), National Recovery and Resilience Plan (NRRP), project MNESYS (PE0000006) – A Multiscale integrated approach to the study of the nervous system in health and disease (DN. 1553, 11.10.2022).
Ethical statement
The study was approved by the Ethics Committee of Bari Policlinico General Hospital (approval code: 7737, 14/06/2023) and conducted in accordance with international ethical standards, including the principles outlined in the Declaration of Helsinki. The participants provided their informed consent.
