Opsoclonus myoclonus ataxia syndrome, ovarian teratoma and anti-NMDAR antibody: an 'unresolved' mystery.

Background: Opsoclonus-myoclonus-ataxia syndrome (OMAS) is characterised by the combination of opsoclonus and arrhythmic action myoclonus with axial ataxia and dysarthria. In adults, a majority are paraneoplastic secondary to solid organ tumours and could harbour antibodies against intracellular epitopes; however, certain proportions have detectable antibodies to various neuronal cell surface antigens. Anti-N-methyl-D-aspartate (NMDAR) antibodies and ovarian teratomas have been implicated in OMAS. Methods: Report of two cases and review of literature. Results: Two middle-aged women presented with subacute-onset, rapidly progressive OMAS and behavioural changes consistent with psychosis. The first patient had detectable antibodies to NMDAR in the cerebrospinal fluid (CSF) alone. Evaluation for ovarian teratoma was negative. The second patient had no detectable antibodies in serum or CSF; however, she had an underlying ovarian teratoma. Patient A was treated with pulse steroids, therapeutic plasma exchange (TPE) followed by bortezomib (BOR) and dexamethasone, while patient B was treated with steroids, TPE followed by surgical resection of ovarian teratoma. Both patients had favourable outcomes and were asymptomatic at the 6 monthly follow-up. Conclusions: With coexistent neuropsychiatric manifestations, OMAS can be considered a distinct entity of autoimmune encephalitis, pathogenesis being immune activation against known/unknown neuronal cell surface antigens. The observation of absence of anti-NMDAR antibody in patients with teratoma-associated OMAS and vice versa is intriguing. Further research on the potential role of ovarian teratoma in evoking neuronal autoimmunity and its targets is required. The management challenge in both cases including the potential use of BOR has been highlighted.