Video-Polysomnography in Peripheral Nerve Hyperexcitability: Clues to Morvan Syndrome in Two Patients and Literature Review

Peripheral nerve hyperexcitability syndromes are characterized by spontaneous motor discharges, fasciculations, and cramps. Morvan syndrome differs from Isaacs syndrome by its central nervous system involvement, autonomic dysfunction, and profound sleep disruption, often presenting as agrypnia excitata. We report two seropositive patients with cramps, fasciculations, insomnia, and autonomic dysfunction but without neuropsychiatric features. Case 1, a 49-year-old man, had LGI1 antibodies and presented with insomnia and autonomic symptoms. Video-polysomnography revealed severe insomnia with absent N3/REM sleep, reduced spindles and K-complexes, and oneiric stupor behaviors. Case 2, a 25-year-old woman, had LGI1 and CASPR2 antibodies, neuropathic pain, and fasciculations. Video-polysomnography demonstrated REM sleep without atonia, rapid N1-to-REM transitions, and microstructural abnormalities of N2 sleep. Tumor screening was negative in both; both improved with immunotherapy. A literature review confirms that video-polysomnography consistently reveals central involvement in Morvan syndrome, characterized by loss of sleep spindles, K-complexes, and pathological REM features, while Isaacs syndrome preserves normal sleep structure. Video-polysomnography is therefore an essential tool to detect subclinical central nervous system dysfunction in Morvan syndrome, especially when neuropsychiatric symptoms are absent, and helps distinguish it from Isaacs syndrome.