Abstract
Opsoclonus-myoclonus-ataxia syndrome (OMAS) is a rare immunological central nervous system disorder that mostly affects children, and it is extremely uncommon in adults. It usually presents idiopathically, as a parainfectious condition, or as a paraneoplastic syndrome. We present a case of a patient who developed adult-onset opsoclonus-myoclonus-ataxia syndrome (OMAS) without any associated infectious or neoplastic disease, a condition that is considered very rare in Central America. This study aimed to document a rare case of adult-onset opsoclonus-myoclonus-ataxia syndrome in a 39-year-old female, highlighting its atypical presentation and the diagnostic challenges involved. The patient presented with a one-week history of rapid-onset and progressive dizziness, nausea, and vomiting, associated with a two-day history of gait instability, memory loss, and sleep disturbances. Past medical history was only notable for psoriatic arthritis controlled with methotrexate. The neurologic examination revealed involuntary, rapid, multidirectional eye saccades consistent with opsoclonus, fast-twitching and jerking movements of the head and bilateral upper extremities consistent with myoclonus, and a wide-based gait with instability indicative of ataxia, suggesting a diagnosis of OMAS. There were no motor or sensory deficits, seizures, fever, or symptoms suggestive of infections. Brain magnetic resonance imaging and computed tomography scan of the head, neck, thorax, abdomen, and pelvis with and without contrast showed no abnormalities. Breast, abdomen, and gynecologic ultrasound, esophagogastroduodenoscopy, and colonoscopy showed no lesions suggestive of underlying neoplasia. Cerebrospinal fluid (CSF) analysis showed mild hyperproteinorrhachia and lymphocytic pleocytosis, along with oligoclonal bands. Viral, bacterial, and autoimmune encephalitis panels were negative. CSF bacterial, mycobacterial, and fungi cultures were negative. Serum viral serologies, tumor markers, and antineuronal antibodies were negative. The patient received treatment with plasmapheresis, intravenous immunoglobulin, and methylprednisolone, with significant but partial improvement of her symptoms.