A 19-year-old man presents with recurrent nocturnal attacks of stereotyped bicycling leg movements, pelvic thrusting, and bilateral asymmetric tonic posturing lasting 15–25 seconds, occurring multiple times per night. He maintains awareness during the events with no postictal confusion. Video-EEG monitoring is performed. The pattern marked **B** in the diagram—showing brief hyperkinetic seizure semiology with scalp EEG demonstrating only diffuse muscle artifact and subtle bifrontal or vertex slow waves—is captured during multiple events. Interictal EEG is largely normal. MRI is unremarkable. What is the most likely diagnosis?
A. Psychogenic non-epileptic seizures with normal interictal EEG
B. REM sleep behavior disorder with nocturnal motor automatisms
C. Temporal lobe epilepsy with secondary generalization and postictal confusion
D. Mesial frontal lobe epilepsy arising from supplementary motor area or cingulate gyrus
Explanation
Why "Mesial frontal lobe epilepsy arising from supplementary motor area or cingulate gyrus" is right
The clinical presentation is pathognomonic for mesial frontal lobe epilepsy (MFLE): brief (<30 s) nocturnal hyperkinetic seizures with preserved consciousness, bizarre automatisms (bicycling movements, pelvic thrusting), bilateral asymmetric tonic posturing ("fencing posture"), and minimal or absent postictal state. The EEG pattern marked B—showing diffuse muscle artifact obscuring the ictal discharge with only subtle bifrontal or vertex slow waves—is characteristic of MFLE because the seizure focus lies on the medial surface (supplementary motor area or cingulate) deep within the interhemispheric fissure, far from scalp electrodes and oriented tangentially, making the ictal discharge non-localizing or paradoxical on surface recording. The normal or nonspecific interictal EEG further supports mesial origin. This diagnosis is supported by Harrison's 21e and ILAE 2017 criteria for frontal lobe epilepsy semiology and EEG characteristics.
Why each distractor is wrong
Temporal lobe epilepsy with secondary generalization and postictal confusion: Temporal lobe seizures typically present with impaired consciousness, postictal confusion, and longer duration (>60 s). The preserved awareness and brief duration, combined with the distinctive hyperkinetic semiology and bifrontal EEG pattern, exclude temporal origin. Temporal seizures also show more focal temporal spikes on interictal EEG.
Psychogenic non-epileptic seizures with normal interictal EEG: Although PNES can mimic MFLE and may present with normal EEG, the presence of subtle but consistent bifrontal/vertex EEG changes during the event, coupled with the stereotyped nocturnal pattern and the patient's preserved awareness without the inconsistency typical of PNES, supports organic epilepsy. The SME note explicitly states MFLE was previously misdiagnosed as PNES—the correct diagnosis is MFLE, not PNES.
REM sleep behavior disorder with nocturnal motor automatisms: REM sleep behavior disorder presents with complex motor behaviors during REM sleep but is not associated with EEG changes or seizure-like stereotypy. Critically, RBD does not show the bifrontal/vertex EEG slow waves or muscle artifact pattern seen in B. The presence of EEG abnormalities during events confirms epilepsy, not parasomnia.
High-YieldNEET PG
Mesial frontal lobe epilepsy = brief nocturnal hyperkinetic seizures + preserved awareness + non-localizing scalp EEG (muscle artifact + subtle bifrontal/vertex slowing) due to medial focus far from scalp electrodes.
