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MOG (myelin oligodendrocyte glycoprotein) antibody-associated disease is a spectrum of autoimmune-mediated syndromes typically manifesting as optic neuritis and longitudinally extensive transverse myelitis (LETM). More recently, phenotypes including encephalitis and brainstem syndromes have been described. MOG antibody-associated, MRI-negative LETM have been reported in the literature. We report a case of MOG antibody-associated disease manifesting as MRI-negative encephalitis presenting with rapidly progressive dementia and visual hallucinations.

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A 78-year-old man with history of hypertension, hyperlipidemia presented with 2-week history of progressive encephalopathy, gait difficulty, intermittent expressive aphasia, face and arm automatisms, and vivid visual, tactile, and auditory hallucinations. Patient scored 18/30 on Montreal Cognitive Assessment (MOCA) 18/30 on admission. CT head and MRI brain were unremarkable. Serial LPs demonstrated lymphocytic pleocytosis with elevated total protein and kappa free light chains, but negative for oligoclonal bands, bacterial, fungal and viral etiologies. CSF autoimmune encephalitis panel was also negative VEEG revealed intermittent right temporal lobe slowing with no epileptiform activity or electrographic correlate for the hallucinations. Encephalopathy, hallucinations, and focal neurologic deficits resolved with supportive care alone. Repeat MOCA was 27/30 prior to discharge.

After discharge from the hospital, serum MOG antibody resulted positive with titer 1:100. Outpatient lumbar puncture was repeated 2-weeks post-discharge with downtrending but persistent lymphocytic pleocytosis and elevated total protein. No oral or IV steroids were initiated given resolution of neurologic deficits and return to prior baseline.

MOG antibody-associated encephalitis should be considered as a differential diagnosis of inflammatory encephalitis and should be tested separately as it is not included within the autoimmune encephalitis panel. Negative MRI brain or spinal cord imaging should not preclude physicians from investigating MOG antibody-associated disease. More surveillance and future reporting is needed to establish causality and prognosis.