Acute Cerebellar Manifestations without Limbic Involvement in GABAB Receptor Autoimmune Encephalitis: Case Report and Literature Review

Autoimmune encephalitis is a rapidly progressive inflammatory brain disease. Gamma-aminobutyric acid type B (GABA(B)) receptor autoimmune encephalitis is a rare subtype characterized by distinct clinical features. Diagnosis can be especially challenging when typical limbic symptoms and neuroimaging findings are absent. This case report underscores the importance of identifying this condition and starting immunosuppressive treatment promptly. A 59-year-old man presented with gait disturbances, dysarthria, and severe ataxia without cognitive impairment. Initial examinations, including a brain MRI, were unremarkable, except for an elevated cell count and protein in the cerebrospinal fluid. Despite receiving initial empirical antiviral treatment, his symptoms worsened, prompting the administration of intravenous methylprednisolone and immunoglobulin. After these immunosuppressive therapies, the cerebellar symptoms showed gradual improvement. Subsequent testing for antibodies to the GABA(B) receptor was positive in both the serum and cerebrospinal fluid. Follow-up MRI revealed cerebellar atrophy, consistent with a diagnosis of GABA(B) receptor-associated acute cerebellitis. This case illustrates that cerebellar symptoms can occur in the absence of more common limbic manifestations in GABA(B) receptor autoimmune encephalitis. The progression of cerebellar atrophy following an initially normal MRI is a significant finding that offers supporting evidence for the diagnosis of cerebellitis. A review of the literature identified similar cases of acute cerebellitis without limbic symptoms, although neuroimaging abnormalities in the cerebellum were not reported. Our case underscores the importance of increased clinical awareness and consideration of autoimmune causes, even when neuroimaging appears normal. Early and appropriate immunosuppressive therapy may help change the course of the disease and enhance patient outcomes.