Inferior olive lesions in autoimmune glial fibrillary acidic protein astrocytopathy: a report of two cases

Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy is a newly identified inflammatory nervous system disorder characterized by Immunoglobulin G autoantibodies against GFAP. While several MRI features are considered typical for autoimmune GFAP astrocytopathy, reports of lesions affecting the inferior olivary nucleus (ION) are rare. In this context, we present two cases of autoimmune GFAP astrocytopathy with lesions in the ION. Case 1 involved a 64-year-old man with meningoencephalomyelitis, peripheral neuropathy, and autonomic dysfunction. His brain MRI revealed bilateral ION lesions and changes along the dentato–rubro–olivary pathway, likely indicating hypertrophic olivary degeneration (HOD). Spinal cord MRI showed bilateral T2 hyperintensities in the anterior horns and a longitudinally extensive spinal cord lesion. In Case 2, a 60-year-old man presented with meningoradiculitis. Although he lacked encephalitic symptoms, his brain MRI showed a left ION lesion with radial perivascular enhancement in the periventricular white matter. The olivary lesion was not linked to other abnormalities along the dentato–rubro–olivary pathway, and contrast enhancement appeared in the same region before the T2 lesion was visible. These findings imply that the inferior olivary involvement in Case 2 was a primary inflammatory lesion. Palatal tremor was not observed in either case. In autoimmune GFAP astrocytopathy, lesions in the ION can appear either as a primary inflammatory response or as HOD resulting from disruption of the dentato–rubro–olivary pathway. When ION lesions are detected during an acute phase that suggests inflammation, autoimmune GFAP astrocytopathy should be included in the differential diagnosis.