DPPX antibody-mediated disease mimicking Wernicke's encephalopathy

Anti-dipeptidyl-peptidase-like protein 6 antibody-mediated disease is a rare autoimmune encephalitis typically presenting with diarrhoea and/or weight loss, central nervous system hyperexcitability and cognitive dysfunction. We present a case of a young woman with 10 days of diplopia and unsteadiness in the context of dysthymia and significant weight loss over 2 months. Initial examination demonstrated mixed dysconjugate nystagmus and ataxic gait. Presumed diagnosis was Wernicke's encephalopathy and intravenous thiamine was given, resulting in partial improvement. Subsequent examination revealed hyperekplexia with ocular flutter, cervical dystonia and startle myoclonus. Cerebrospinal fluid indirect immunofluorescence on primate cerebellum revealed granular layer pattern of staining, prompting testing for anti-dipeptidyl-peptidase-like protein antibodies, which returned strongly positive. Given the phenotypic overlap, it is important to consider this rare disorder in the differential diagnosis of Wernicke's encephalopathy. In this case, the emergence of ocular flutter, startle myoclonus and the specific type of nystagmus made it clear there was an alternative diagnosis.