Abstract
Introduction
A vast amount of literature describes the comorbidity of migraine and major depressive disorder (MDD). Comorbidity studies of depression and the two most common types of migraine—migraine with aura (MA) and migraine without aura (MO), consistently report a higher prevalence of migraine among depressed individuals compared to the general population (1–4). There is currently no verified explanation for this comorbidity, although it has been suggested that common biological pathways, such as the serotonergic and dopaminergic system, may be involved (5,6). An important question that needs to be answered is whether depression is associated with a specific subtype or form of migraine. Several studies report that MA is more strongly correlated with depression than MO (1,7–9). One interpretation of this finding is that migraine patients with comorbid depression suffer from a different type of migraine than ‘pure’ migraineurs, which causes them to experience more aura symptoms. Alternatively, however, this finding might indicate that individuals with more severe forms of migraine have a higher risk of developing depression. Given the symptomatic overlap between MO and MA, and the lack of evidence that these two disorders are etiologically distinct subtypes of migraine (10,11) the second interpretation seems to be a plausible explanation.
To investigate whether depression is associated with a specific type of migraine, we reverse the question: are the migraines of depressed and non-depressed individuals similar in characteristics? If there are observable qualitative differences in the manifestation of migraine in depressed and non-depressed individuals, this may indicate there is a difference in the etiology of migraine in both groups. To address this issue, we compared migraine symptomatology in a large sample of MDD patients and in a control sample, selected for low risk of depression. Using latent class analysis (LCA), individuals were empirically classified according to the pattern of headache symptoms they reported. Then the headache symptom profiles were compared between the MDD and the non-MDD groups. Thus, qualitative differences in migraine symptomatology could be assessed while still allowing for anticipated differences in prevalence and severity.
Methods
Sample
The depressed sample in this study consisted of MDD cases diagnosed according to DSM-IV criteria (12) with the Composite International Diagnostic Interview [CIDI] (13). The majority of MDD cases were originally recruited for the Netherlands Study of Depression and Anxiety [NESDA] (14). Of the 2981 NESDA participants, 2601 filled in a self-report questionnaire that provided information on migraine. Of these individuals, 1636 were diagnosed with lifetime MDD (1017 of whom had a diagnosis of MDD in the past year). All individuals with a lifetime diagnosis of MDD were included in this study. Seven hundred fifty-six were recruited through primary care, 561 through specialized mental health care and another 319 from the general population. Individuals who did not have a lifetime MDD diagnosis were not included. All NESDA participants underwent a four-hour baseline assessment at one of seven clinic sites between September 2004 and February 2007. Part of this assessment were an interview on somatic health, functioning and health care use, and the administration of several written questionnaires (15), which included a section on migraine symptomatology (see below). A detailed description of sampling and ascertainment procedures for the NESDA study can be found elsewhere (14).
The remainder of the study sample consisted of volunteer members of the Netherlands Twin Registry (NTR), based at the department of Biological Psychology at VU University in Amsterdam. In this group, the migraine data were collected as part of a longitudinal study on health, lifestyle and personality. The data used in the present study were collected in 2002 and 2004. Data collection procedures are described in detail elsewhere (16,17). These surveys included the same headache section that was included in the NESDA questionnaire. When a participant answered the headache section in both surveys, the most recent (2004) survey was used. Headache data were available for a total of 4047 families. In a subset of these families, one or more individuals had been diagnosed with MDD in an earlier study of anxious depression (18), based on a CIDI interview. In addition, an anxious depression factor score was constructed based on data from the 2002 survey, using several measures of anxiety, depression and neuroticism (see Boomsma et al. (18) for details). The 2004 survey included the NEO Five Factor Inventory (19), which has a neuroticism subscale.
NTR participants with a diagnosis of MDD based on the CIDI interview were included as additional MDD cases. In case of multiple individuals with MDD within a family, the individual with the highest anxious depression or neuroticism score was included. With this procedure an additional 180 MDD cases were selected, resulting in a total number of 1816 individuals with MDD.
The non-depressed control sample was also selected from the NTR, after excluding the families in which one or more individuals had been diagnosed as MDD cases. One person was selected from each family to maintain a selection of unrelated controls. Within each family, individuals were ranked based on their anxious depression score. This information was available for 3209 families. In families with no anxious depression scores available (
The control sample included 1379 male and 2049 female participants. The MDD sample included 553 males and 1263 females. The mean age was 42.6 (±12.4) in the MDD sample and 41.1 (±14.0) in the control sample.
Migraine measures
Headache questions included in the surveys and correspondence to IHS diagnostic criteria for migraine*
IHS, International Headache Society. *In the present study, individuals were considered positive for a full IHS migraine diagnosis if they fulfilled the following criteria: A; B; at least two of C2, C3 and C4; at least one of D1 and D2.†An attack frequency of ‘several times a year’ or more was assumed to be equivalent to >= 5 episodes.††The official criteria do not include osmophobia and require both photo- and phonophobia, however, from these data it was not possible to determine whether both were present.
The information obtained from the questionnaire items was recoded as follows: 0 = screened negative, 1 = screened positive, but negative for symptom, 2 = screened positive, and positive for symptom. This was done for the variables
Statistical analyses
LCA (21,22) is a statistical method that classifies individuals based on their pattern of responses or characteristics. A latent class model describes the relationship between a set of categorical observed variables (indicators) and an unobserved categorical variable. The categories of this underlying variable are referred to as latent classes, or clusters. Within each cluster, the observed variables are assumed to be independent. In other words, the relationship between the observed variables (in this case, migraine symptoms) is explained entirely by the latent variable (in this case, ‘type of headache’). The parameters in an LCA model are the prevalence of each class, and the probability, given class membership, that an individual is positive for each symptom (the conditional probabilities). They are estimated with the expectation-maximization (EM) algorithm (23). For each individual, the most likely class membership can then be calculated, based on the pattern of symptoms reported.
The aim of this study was to determine whether the same latent classes of headache sufferers could be identified in the MDD patients and the controls. We first estimated the number of latent classes present in the two samples. Then the symptom profiles of each group were compared by running a multiple-group LCA with the headache symptoms as the indicator variables. Differences in the symptom profiles were tested by equating the conditional probabilities for the classes across groups, and assessing the change in model fit by comparing log-likelihood values. Because migraine is known to be more prevalent in females than in males, it was first tested whether symptom profiles differed across sex. Next, profile differences between the MDD patients and the controls were assessed. Finally, classification results were compared between the two groups to test for differences in prevalence. All latent class analyses were performed in Mplus version 5 (Muthén & Muthén Los Angeles, CA, USA), using the “KNOWNCLASS” option to allow multi-group LCA. The number of random sets of starting values for the initial stage was set to 250 and in the final stage 50 maximum likelihood optimizations were specified. The number of classes was determined using the Bayes Information Criterion (BIC), with a lower BIC indicating better fit to the data.
Results
The prevalence of migraine symptoms and IHS migraine diagnosis in the depressed and non-depressed groups
MDD+, depressed; MDD−, non-depressed; OR, odds ratio indicating risk of each symptom/diagnosis, given depression status; CI, confidence interval; IHS, International Headache Society.
Initially, an exploratory LCA was performed to determine the appropriate number of classes and to compare the symptom profiles in males and females. A two-group analysis was run with sex as the grouping (“KNOWNCLASS”) variable, thus allowing for different symptom profiles in males and females. Sex was also modeled as a covariate on class membership, to allow for different migraine prevalences in males and females. This analysis was run first on cases only, and then on controls only. Based on the BIC values, a three-class model had the best fit to the data in both the cases and the controls: in cases, the three-class model produced a BIC of 13542, compared to a BIC of 13671 for a two-class model and BIC of 13760 for a four-class model; in controls, the three-class model produced a BIC of 16112, compared to a BIC of 16209 for a two-class and BIC of 16348 for a four-class model.
Model fit statistics and comparisons for the baseline and restricted three-class LCA models
LCA, latent class analysis; npar, number of parameters; LL, Log-likelihood; d.f., degrees of freedom.
As the symptom profiles did not differ between males and females, we proceeded with a two-group model (with three classes) in which the conditional probabilities were equal for males and females but differed between the MDD and control group. Sex and case/control status were maintained in the model as covariates, because of the known differences in migraine prevalence across these groups. Figure 1 shows the symptom profiles for this model, with the symptoms on the x-axis, the conditional probabilities for each symptom on the y-axis and the error bars indicating 95% confidence intervals. Class 0 represents the group of individuals screening negative for headaches, who did not answer further questions. These individuals have conditional probabilities of 0 for all symptoms. Class 1 individuals have headaches with migrainous features, but most of these would not be diagnosed as migraine patients. The individuals in class 2 can be characterized as migrainous headache sufferers, with headaches that typically include the majority of migraine features. The most important difference between class 1 and class 2 appears to be the overall severity of the headaches. Class 1 and class 2 look similar, but all symptoms are more prevalent in class 2. The distinction between class 1 and class 2 is most pronounced for the symptoms Symptom profiles for the two-group, three-class model, with the symptoms on the x-axis, the conditional probabilities for each symptom on the y-axis and the error bars indicating 95% confidence intervals. Class 0 represents the group of individuals screening negative for headaches, who did not answer further questions.
It can be seen that the profiles of MDD and non-MDD subjects are very similar, although some subtle differences are observed in the prevalence of
Class prevalences in the four analysis groups (male/female, depressed/non-depressed), based on best-fitting model
MDD+, depressed; MDD−, non-depressed.
Discussion
The aim of this study was to compare migraine symptom profiles in MDD patients and controls, empirically classified according to their pattern of headache symptoms. If similar headache classes and symptom profiles would arise empirically and independently in MDD patients and controls, this would be consistent with the hypothesis that we are observing the same disorder in the two groups. Substantial qualitative differences, however, would suggest a difference in etiology.
As expected, the prevalence of migraine was higher in MDD patients. Importantly, all migraine symptoms had an increased prevalence in the MDD group, and MDD patients were overrepresented in both the mild and severe migraine classes. This is consistent with the literature on the comorbidity of migraine and MDD. Qualitatively, however, migraine was very similar in MDD patients and controls. Similar symptom profiles were observed in the two groups, although a few differences should be mentioned. The most pronounced difference between MDD and non-MDD subjects is in the higher prevalence of
Although the observed differences are small and subtle, they are significant (additional analyses in which the
Strengths and limitations
To our knowledge, this is the first study in which migraine symptomatology in MDD patients and controls is compared while taking into account expected differences in prevalence and severity. Figure 1 shows that more severely affected patients have a higher probability of all symptoms, but in particular
Another major strength of this study is the sample size, which is quite large compared to other studies of the comorbidity of migraine and depression. A total of 1816 clinically diagnosed MDD patients and 3428 controls selected for low risk of MDD participated, all of whom provided detailed information on migraine symptomatology.
At the same time, however, one potential limitation of this study is related to the sample size. Although the results of the LCAs in this study show considerable similarity to those we reported previously (10,11), in previous studies the best-fitting model was a 4-class rather than a three-class model. This is almost certainly a consequence of the larger sample sizes in these studies, which allowed the distinction of a fourth class. However, the additional class estimated in the previous studies reflected a less severe, non-migrainous form of headache on the same continuum of liability, and as noted in our previous twin studies, a three-class model captures most of the variance in migraine status that is captured by a four-class model. In addition, given that the current sample size (1816 cases and 3428 controls) is still quite large, any qualitative differences that can only be detected in larger samples would most likely be of little practical importance in distinguishing between ‘pure migraine’ and MDD-related migraine.
A second limitation concerns the questionnaire. Because no information was available on unilaterality of the headache, we cannot exclude the possibility that the frequency of unilateral headache may be different in MDD patients and controls. However, because patients were required to have at least two out of the three measured C criteria (see Table 1) to receive a migraine diagnosis, it is unlikely that the lack of information on unilateral headache has caused false-positive endpoint diagnoses. Indeed, the observed prevalence of migraine according to ICHD-II criteria was 3% (males) and 10% (females) in the low-risk control sample, and 4% (males) and 13% (females) in the total, unselected NTR sample (
Generalizability
The NTR is a population-based registry of unselected twin families. A non-response study found no evidence that participants’ willingness to participate was related to migraine status (17). Whether findings in twins can be generalized to the singleton population can be tested by including data from the twins’ siblings. In this study, twins had the same prevalence of each class of migrainous headache as their singleton siblings (χ2(2)=1.617,
Conclusions and implications
Two important observations were made in this study. Firstly, the prevalence of
A second important observation is that the migraine symptom profiles of MDD patients and non-depressed controls are very similar, suggesting that a similar disease process underlies migraine in both groups. We observed a slightly increased prevalence of
This highlights the importance of collecting additional information besides those that make up the official diagnostic criteria for a given disorder. Information on the presence of comorbid MDD (symptoms) may be vital for any study investigating the etiology of migraine. This may also extend to other traits. Many disorders show comorbidity with migraine, in particular psychiatric disorders (depression, anxiety, bipolar disorder, phobias and panic disorder) (3,5,22), but also non-psychiatric disorders such as stroke, asthma, epilepsy, endometriosis and other chronic pain conditions (27–33). Similarly, depressed individuals show an increased prevalence of a variety of somatic symptoms, compared to non-depressed subjects (34), and a recent study demonstrated that migraine was an important predictor of other somatic symptoms in depressed subjects (35). In this context, it is interesting to mention the reported comorbidity between MDD and general chronic pain (36). Indeed, the MDD patients from the NESDA study reported a remarkably high frequency of pain symptoms, often at multiple sites (in the NTR these data were not available). While this might reflect a general tendency of depressed patients to more easily endorse questions regarding somatic complaints, it has been suggested that chronic pain might in fact be a symptom of depression (37). Although beyond the scope of the present study, this is a fundamental issue with important implications for research on migraine comorbidity. In conclusion, the collection of extensive and detailed information on comorbid disorders in studies of migraine could potentially improve our understanding of the etiology of these disorders and may contribute toward a more effective study of their underlying causes.
Financial support
This work was supported by Spinozapremie (NWO/SPI 56-464-14192), Center for Medical Systems Biology (NWO Genomics), Twin-Family Database for Behavior Genetics and Genomics Studies (NWO 480-04-004), Borderline Personality Disorder Research Foundation and genome-wide analyses of European twin and population cohorts (EU/QLRT-2001-01254). The infrastructure for the NESDA study (www.nesda.nl) is funded through the Geestkracht program of the Netherlands Organization for Health Research and Development (ZonMw, grant number 10-000-1002) and is supported by participating universities and mental health care organizations (Virije University Medical Center, GGZ inGeest, Arkin, Leiden University Medical Center, GGZ Rivierduinen, University Medical Center Groningen, Lentis, GGZ Friesland, GGZ Drenthe, Scientific Institute for Quality of Health Care [IQ Healthcare], Netherlands Institute for Health Services Research [NIVEL] and Netherlands Institute of Mental Health and Addiction [Trimbos]).
