Objective: To report a case of opsoclonus-myoclonus-ataxia syndrome (OMAS) due to autoimmune GFAP astrocytopathy.

Background: OMAS is associated with brainstem pathology. In adults, common causes include presumed autoimmune brainstem encephalitis or postinfectious processes, as specific antibodies are often undetected. Autoimmune GFAP astrocytopathy has diverse clinical and radiological features, but is rarely linked to OMAS.

Method: Case report.

Results: A 15-year-old Thai boy had fever and headache for 10 days, followed by progressive ataxia, bilateral leg weakness, urinary retention, and myoclonus. Exam showed ocular flutter, upper extremity myoclonus, and ataxia, consistent with OMAS. Additional findings included bilateral hip flexor weakness (grade 3), hyporeflexia at knees and ankles, and nuchal rigidity. CSF analysis revealed lymphocytic pleocytosis, elevated protein, and low glucose, suggestive of acute meningitis. Despite antibiotics, symptom improvement was modest. CSF studies including Gram stain, culture, meningitis/encephalitis panels were negative, as were paraneoplastic and autoimmune panels. Brain and spinal MRI showed subtle T2/FLAIR hyperintensities in the basal ganglia, meningeal enhancement around the brainstem and spinal cord, and an intramedullary lesion in the lower thoracic cord and cauda equina. No intrinsic brainstem lesion was found. Autoimmune GFAP meningoencephalomyelitis was suspected, and CSF anti-GFAP antibodies confirmed the diagnosis. High-dose intravenous corticosteroids (5 days, followed by bimonthly and monthly doses) led to significant improvement. The absence of an intrinsic brainstem lesion on MRI does not exclude microscopic inflammation, as seen in many OMAS cases with normal MRI. Meningeal enhancement suggests inflammatory involvement of the brainstem. This is only the second reported case of OMAS associated with autoimmune GFAP astrocytopathy. The previously reported case had ocular flutter and ataxia but no myoclonus [1].

Conclusion: Autoimmune GFAP astrocytopathy should be recognized as a potential etiology of OMAS. This may still be under-recognized. Clues include low CSF glucose, meningeal enhancement, and brainstem or spinal cord lesions. Perivascular radial enhancement may be absent. Early recognition is crucial, as corticosteroids are highly effective and should be prioritized over other immunotherapies or plasma exchange.

References: 1. Wada T, Higashiyama Y, Kunii M, et al. Ocular flutter as the presenting manifestation of autoimmune glial fibrillary acidic protein astrocytopathy. Clin Neurol Neurosurg. 2022;219:107307.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/autoimmune-gfap-astrocytopathy-as-an-etiology-of-opsoclonus-myoclonus-ataxia-syndrome/