Epilepsia Partialis Continua in an Adolescent: A Case of Diagnostic Overshadowing

Abstract

Epilepsia partialis continua is an uncommon form of focal status epilepticus characterized by continuous focal motor activity with preserved awareness. In adolescents with psychiatric comorbidity, these movements may be mistaken for functional or compulsive behavior, a phenomenon that may reflect diagnostic overshadowing, the misattribution of neurological or medical symptoms to a preexisting psychiatric condition. A 15-year-old boy with anxiety disorder, obsessive compulsive disorder, and panic disorder presented with a two week history of persistent right toe and foot tapping that spread proximally and became painful. His family reported that the movements continued during sleep, although inpatient observation showed that they occasionally paused or disappeared. This inconsistency contributed to an early impression of a psychogenic process and led to the deferral of neuroimaging. Continuous video EEG subsequently demonstrated frequent, rapidly recurring epileptiform discharges over the left central region that corresponded to the right foot movements, confirming epilepsia partialis continua. Treatment with lacosamide and clobazam led to complete resolution of the movements and pain within 24 hours. Subsequent brain MRI was unremarkable, and symptoms remained controlled on follow up. This case illustrates how psychiatric history can shape diagnostic reasoning and delay recognition of epilepsia partialis continua. Persistent focal motor activity, even when intermittently suppressible or behaviorally ambiguous, should prompt early consideration of this diagnosis and escalation to prolonged video EEG when routine evaluation is inconclusive, enabling accurate diagnosis and effective seizure control.

Introduction

Epilepsia partialis continua (EPC) is a rare variant of focal status epilepticus characterized by a persistent, rhythmic movement of a limb (most commonly a distal extremity) while the patient maintains consciousness. Children presenting with EPC require a structured clinical, electroencephalographic (EEG), and radiologic evaluation to differentiate among potential etiologies and guide timely diagnosis. ¹ The difficulties of the diagnostic process in pediatric EPC include the variety of etiologies of the condition, in addition to the need to distinguish EPC from discrete focal motor seizures and other mimics.

Psychiatric illnesses occur frequently in individuals with epilepsy. Approximately one-third of individuals with epilepsy will experience a psychiatric illness in their lifetime, often a mood or anxiety disorder. ²

When an individual with a psychiatric illness experiences atypical or prolonged motor symptoms, clinicians may inadvertently attribute the physical symptoms to a purely psychological cause.^3,4 This cognitive bias, known as diagnostic overshadowing, has been increasingly recognized as a major contributor to misdiagnosis and delayed proper care, particularly in acute and inpatient settings.^3,4

EEG plays a central role in the diagnosis of EPC, and an extended video-EEG is often necessary. Because seizures may persist for hours to days and electrographic findings can be subtle or difficult to interpret, routine EEG may not capture ictal activity or clearly demonstrate seizure evolution. In some cases, EEG findings may be non-specific or non-diagnostic despite ongoing focal motor activity, highlighting the importance of maintaining a high degree of clinical suspicion and correlating findings with the clinical examination. Accordingly, extended video-EEG monitoring can be particularly helpful when focal movements persist without a clear etiology. ⁵

Case Presentation

A 15-year-old boy whose past medical history comprised anxiety disorder, obsessive-compulsive disorder (OCD), and panic disorder presented to the emergency department after experiencing a 2-week history of continuous “tapping” in his right foot. The tapping initially started in his first toe, then progressively worsened, spreading to his entire right foot and producing pain radiating to the knee. The movements were reportedly continuous and persisted during wakefulness and sleep. Repositioning, stretching, massaging, and using ibuprofen provided no relief. Consequently, the patient’s psychiatrist was consulted and suggested tapering off Lexapro, which was recently started, and trying diphenhydramine; however, neither intervention improved the symptoms.

The patient arrived at the emergency department with vital signs within normal limits and was alert and oriented. Physical examination revealed continuous clonic movements of the right great toe and foot, without weakness or sensory deficits. Laboratory tests revealed a white blood cell count of 10.7 K/µL, an anion gap of 17 mmol/L, an AST of 73 U/L, an ALT of 98 U/L, and a glucose level of 165 mg/dL. Radiographs of the right foot were negative. Neuroimaging was deferred during the initial evaluation because the movements were considered most consistent with a psychogenic process.

The patient was admitted to the hospital and solely observed for the first 24 hours. The abnormal movements were observed while the patient was awake and did not improve with different examination strategies, such as passive manipulation of the toes, ankle, and knee. During sleep, the movements were very subtle and at times were absent. The patient was evaluated by the neurology service and placed on continuous video-EEG monitoring. Monitoring demonstrated frequent epileptiform discharges over the left central region with consistent electroclinical correlation to the right toe and foot movements, confirming the diagnosis of epilepsia partialis continua.

After initiating treatment with lacosamide and clobazam, the patient’s movement and associated pain ceased within 24 hours. The mild transaminitis and hyperglycemia found on admission were thought to reflect physiologic stress from prolonged focal motor activity or baseline effects of psychotropic medications; these values normalized on repeat testing and were not relevant to the underlying neurologic process. The patient was discharged from the hospital and underwent an outpatient MRI of the brain, which was negative for structural abnormalities. He continues to follow up with neurology with well-controlled symptoms. Follow-up at 3 months showed continued control without recurrence of motor activity or pain.

Discussion

The differential diagnosis for persistent focal motor activity in an adolescent includes tics, stereotypies, medication-related movement disorders such as akathisia, focal motor seizures without EPC, functional neurological disorder, movement disorders such as dystonia, and peripheral neuromuscular conditions including radiculopathy. In this case, the rhythmic and progressive nature of the movements, the persistence during sleep, and the absence of voluntary suppression made non-epileptic etiologies less likely. The lack of associated sensory deficits or weakness further reduced suspicion for peripheral neuromuscular causes. Ultimately, the demonstration of a consistent electroclinical correlate on video-EEG confirmed the diagnosis of EPC and distinguished it from these mimics.

Diagnostic overshadowing occurs when clinicians attribute physical symptoms to an existing psychiatric diagnosis rather than pursuing alternative medical explanations.^3,4 In this case, the patient’s history of OCD and anxiety created a cognitive “lens” through which the rhythmic toe tapping was interpreted. The clinical team anchored on a behavioral explanation, leading to premature diagnostic closure and deferral of neuroimaging. This anchoring was reinforced when the movements became subtle during sleep, which was interpreted as behavioral cessation rather than variability in seizure expression. Prolonged video-EEG later established a clear electroclinical correlate and confirmed EPC.

This case reflects broader evidence that psychiatric comorbidity can complicate the evaluation of suspected epilepsy and is associated with an increased risk of diagnostic overshadowing and delayed recognition of neurologic disease.^2-4 Because EPC often presents with preserved awareness and subtle focal motor activity, accurate diagnosis relies on careful clinical assessment together with EEG findings.^5,6 Although persistence of motor activity during sleep may support the diagnosis, variability in clinical and electrographic expression, including potential mismatch between observed movements and EEG findings, can contribute to diagnostic uncertainty. These factors underscore the role of prolonged video-EEG monitoring when clinical suspicion remains high.^5,6

EEG is an important tool in the evaluation of EPC. But electrographic findings may be variable and diagnosis often relies on careful clinical correlation. In cases of persistent clinical concern, extended video-EEG monitoring may be helpful to improve diagnostic yield. ⁵ Additionally, some individuals with EPC may exhibit normal results from standard EEG recordings, pointing out the importance of high clinical suspicion. In this case, the patient underwent 24 hours of continuous video-EEG monitoring, revealing multiple episodes of focal discharges in the left central region that correlated with movements of the right toe and foot. These findings definitively established the diagnosis of EPC and distinguished it from a functional etiology. Prior literature highlights the need for prolonged or repeated EEG recordings when routine studies are inconclusive. ⁵

Treatment of EPC can be challenging, and many patients require escalation beyond initial antiseizure monotherapy to achieve seizure control. ⁶ When an autoimmune etiology is suspected, immunotherapy may be required in addition to antiseizure medications. ⁷ In contrast, our patient experienced complete resolution of motor activity and pain within 24 hours of initiating lacosamide and clobazam, with sustained seizure control at 3-month follow-up. This case illustrates how timely recognition of EPC can facilitate prompt treatment and rapid clinical improvement (Figure 1).

Figure 1.

Electro-clinical correlate of epilepsia partialis continua (EPC). A representative 10-second video- EEG epoch captured during a 17-hour continuous monitoring session. Shown in a longitudinal bipolar montage, a localized run of irregular, fast, focal sharp/spiky discharges is maximal over the left central region (F3–C3 and C3–P3), with electrographic field extension to the midline central channels (Fz–Cz and Cz–Pz). The onset and maximal amplitude of these cortical discharges are strictly time-locked to the videodocumented clinical event (indicated by the vertical timeline/arrowhead), which captured continuous clonic movements of the patient’s right first toe

Conclusion

In children and adolescents, the presence of continuous, repetitive motor activity that persists during sleep, coupled with focal EEG abnormalities, is highly suggestive of EPC. This case report presented here demonstrates the risk of “diagnostic overshadowing” when a patient has psychiatric and neurological comorbidities. It illustrates the importance of long-term video-EEG monitoring, an awareness of the spatial limitations of EEG recordings, and a collaborative approach between disciplines for the proper diagnosis and treatment of this complex neurological disorder.