A 45-year-old man presents with a 3-month history of severe insomnia, visual hallucinations, profuse sweating, and continuous fine rippling muscle contractions in his limbs. Examination reveals myokymia, tachycardia, and hypertension. Brain MRI shows mesial temporal T2/FLAIR hyperintensity. His EEG is shown in the diagram. The pattern marked **B** (bitemporal slowing with TIRDA and epileptiform discharges) is characteristic of which autoimmune encephalitis syndrome?
A. Morvan syndrome (CASPR2-antibody-mediated autoimmune encephalitis with peripheral nerve hyperexcitability and autonomic dysfunction)
B. Anti-NMDA receptor encephalitis with prominent psychiatric and movement disorder features
C. Hashimoto encephalopathy with reversible posterior leukoencephalopathy
D. LGI1-antibody limbic encephalitis with faciobrachial dystonic seizures and hyponatremia
Explanation
Why Morvan syndrome (CASPR2-antibody-mediated) is right
Morvan syndrome is a rare autoimmune disorder mediated by antibodies against CASPR2 (contactin-associated protein-like 2), a component of the VGKC complex. It presents with a clinical tetrad: (1) peripheral nerve hyperexcitability (neuromyotonia/myokymia with EMG showing 150–300 Hz discharges), (2) autonomic dysfunction (profuse sweating, tachycardia, hypertension), (3) severe CNS manifestations (insomnia, hallucinations, memory impairment, behavioral change), and (4) pain. The EEG pattern marked B—bitemporal slowing, TIRDA (temporal intermittent rhythmic delta activity), and interictal epileptiform discharges—is the hallmark EEG finding in Morvan syndrome, reflecting the limbic encephalitis component. MRI shows mesial temporal T2/FLAIR hyperintensity. Diagnosis is confirmed by serum and CSF CASPR2 antibodies (cell-based assay). This patient's constellation of myokymia, autonomic dysfunction, insomnia, hallucinations, and the characteristic EEG pattern is pathognomonic for Morvan syndrome (Brain 2023; Lancet Neurol 2022).
Why each distractor is wrong
LGI1-antibody limbic encephalitis: While also a VGKC-complex-associated autoimmune encephalitis, LGI1 antibodies cause a distinct syndrome characterized by faciobrachial dystonic seizures (not myokymia), hyponatremia (not a feature of Morvan), and a different clinical phenotype. EEG findings differ, and the peripheral nerve hyperexcitability tetrad is absent.
Anti-NMDA receptor encephalitis: Presents with prominent psychiatric symptoms, movement disorders (orofacial dyskinesias, autonomic instability), and seizures, but lacks the characteristic myokymia, neuromyotonic discharges, and the specific bitemporal TIRDA pattern. CSF findings typically show lymphocytic pleocytosis and oligoclonal bands, not CASPR2 antibodies.
Hashimoto encephalopathy: A steroid-responsive encephalopathy associated with thyroid peroxidase antibodies, presenting with cognitive decline, seizures, and reversible posterior leukoencephalopathy on MRI. It does not feature myokymia, autonomic dysfunction, or the characteristic bitemporal TIRDA pattern seen in Morvan syndrome.
High-YieldNEET PG
Morvan syndrome = CASPR2 antibodies + myokymia + autonomic dysfunction + severe insomnia + bitemporal TIRDA on EEG; associated with thymoma in 40–50% of cases.
