Unilateral Cortical Ribboning and Corticomedullary Lesions in a Rare Case of Coexisting Anti-N-methyl-D-aspartate...

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is an autoimmune disorder characterized by psychiatric manifestations, seizures, and dyskinesias. Neuronal intranuclear inclusion disease (NIID) presents heterogeneously with dementia, neuropathy, and episodic encephalitis-like events, typically showing bilateral corticomedullary hyperintensities on diffusion-weighted imaging (DWI). The simultaneous occurrence of these conditions is extremely uncommon, complicating diagnosis due to overlapping clinical and radiological features. We report the case of a 68-year-old female with a history of atrial fibrillation and hyperthyroidism who presented with urinary tract infection, followed by acute consciousness disturbance, left arm paresis, and pyrexia. Initial antibiotic therapy resolved symptoms, but recurrent neurological deficits ensued. Diagnostic evaluation confirmed the presence of both anti-NMDAR encephalitis, evidenced by positive serum antibodies, and NIID, supported by abnormal GGC repeat expansions in the NOTCH2NLC gene and intranuclear inclusions on skin biopsy. Brain magnetic resonance imaging demonstrated unusual unilateral cortical ribboning and corticomedullary lesions on DWI. Therapy with corticosteroids and intravenous immunoglobulin resulted in significant improvement; however, subsequent workup revealed colorectal adenocarcinoma. This case highlights the diagnostic complexity and management challenges by the rare concurrence of anti-NMDAR encephalitis and NIID.