Isolated opsoclonus heralding neuromyelitis optica spectrum disorder

Opsoclonus is an ocular motility disorder characterized by spontaneous, arrhythmic conjugate saccades of varying amplitude occurring in all directions of gaze without normal intersaccadic interval. Etiological spectrum of opsoclonus encompasses paraneoplastic and neoplastic conditions, infectious and para-infectious encephalitis, autoimmune, metabolic and toxic encephalopathies, drugs, motor neuron diseases, multiple sclerosis and rarely neuromyelitis optica spectrum disorder (NMOSD). Opsoclonus has never been reported as a presenting manifestation heralding NMOSD. We herein report a previously healthy 37-year-old Asian Indian woman who presented with oscillopsia and opsoclonus, followed, 12 h later, by right-sided hemiparesis, right-sided appendicular ataxia, and left-sided lower motor neuron type facial palsy and dysarthria. Brain magnetic resonance imaging revealed hyperintense lesions in brainstem and thalamus in T2-weighted and fluid attenuated inversion recovery-weighted images, quite suggestive of NMOSD. Serum and cerebrospinal fluid samples were positive for anti-aquaporin-4 antibodies, which clinched the diagnosis of seropositive NMOSD. After completion of a course of intravenous methylprednisolone 1 g/day for 5 days, her opsoclonus disappeared completely. There was significant improvement in her speech and weakness within the first week of therapy and no objective deficit after day 20 of admission. After one-and-a-half-year follow-up, the patient was maintaining well on rituximab as secondary prophylaxis without any further attack. Our case highlights that isolated opsoclonus can be the presenting feature of NMOSD.