Morvan Syndrome Masquerading as Anxiety Disorder: A Case Report Highlighting the Importance of Recognizing Organic Signs in Psychiatric Settings.

Morvan syndrome is a rare subtype of autoimmune encephalitis, primarily characterized by increased peripheral nerve excitability, autonomic dysfunction, and severe insomnia. This report presents a 28-year-old female patient who sought medical attention due to widespread pain, refractory insomnia, limb sensory abnormalities, and low mood, initially diagnosed as "anxiety disorder". Neurological examination revealed muscle twitching in the limbs. Electromyography indicated increased peripheral nerve excitability, with serum testing showing weak positivity for anti-Leucine-rich Glioma Inactivated 1 (LGI-1) IgG antibodies and strong positivity for anti-Contactin-associated Protein-like 2 (CASPR2) IgG antibodies. Cerebrospinal fluid Pandy's test was weakly positive. The final diagnosis was Morvan syndrome complicated by anxiety disorder. Following treatment, the patient's symptoms significantly improved. This case highlights the diagnostic challenges of Morvan syndrome, particularly when patients present with prominent psychiatric symptoms that mimic functional disorders. It underscores the critical importance of screening for subtle organic signs-specifically fasciculations and widespread pain-in patients with refractory anxiety to prevent misdiagnosis and facilitate timely immunotherapy.