Opsoclonus Myoclonus Ataxia Syndrome With Anti–Glutamic Acid Decarboxylase Antibody Positive: Response to Plasma Exchange

Abstract

Objectives Opsoclonus myoclonus syndrome (OMS) is a very rare neurological disorder of probably autoimmune origin. Glutamic acid decarboxylase antibody (GAD-Ab) is one of many antibodies that have been associated with OMS. Common treatments include intravenous immunoglobulin (IVIG) and corticosteroids. To our knowledge, this is the fourth case of GAD-Ab-positive OMS reported and the first one responsive to plasma exchange (PLEX). Clinical Presentation The patient is a 77-year-old male who presented with new-onset tremors and gait disorder. He had been diagnosed with OMS and positive GAD-Ab 2 years ago. At the time of diagnosis, his condition was not responsive to IVIG or corticosteroids and seemed to improve following PLEX. He made a near full recovery and was prescribed a low dose of mycophenolate. The patient reported worsening in tremor and gait over the last several days. This was the first time he had signs of clinical relapse since diagnosis. His labs were notable for hyponatremia, elevated glucose, and acute kidney injury. Brain CT showed intracranial atherosclerosis and age-indeterminate generalized cortical atrophy, perhaps due to chronic microangiopathic white matter changes. GAD-Abs assessed on this admission were zero (normal is less than 5), whereas they were 143 before treatment 2 years ago, although no GAD-Ab titer was measured after PLEX. The patient received five sessions of PLEX with overall improvement. Conclusion We reported a rare case of OMS with positive GAD-Ab who responded to PLEX. GAD-Ab may be a predictive marker of patient symptoms and is recommended to be measured in patients with OMS before and after treatment.