Rapidly Progressive Corticobasal Degeneration Mimicking Brainstem Encephalitis

Corticobasal degeneration (CBD) may have a rapidly progressive (RP) clinical course, mimicking other neurological conditions.

To describe a neuropathologically proven case of RP-CBD in a patient initially diagnosed with immune-mediated brainstem encephalitis.

Retrospective data collection from electronic records and authorized video material.

A 51-year-old man presented with bilateral ptosis, diplopia, and dysphagia. The diagnostic workup was negative for myasthenic syndromes. He progressively developed cognitive dysfunction with frontal release signs and asymmetric parkinsonism. Cerebrospinal fluid evaluation revealed 4 leukocytes/uL, 0.32 g/L proteins, 0.85 g/L glucose, and absent oligoclonal bands. Weakly positive anti-PNMA2 (Ma2/Ta) antibodies were present, and magnetic resonance imaging showed a T2 hyperintensity involving the midbrain and pons. Based on these features, the diagnosis of immune-mediated brainstem encephalitis was considered. The patient did not improve after several cycles of methylprednisolone, intravenous immunoglobulin, and plasma exchange. At 1 year after onset, he developed horizontal and vertical gaze limitation and worsening of the parkinsonism and cognitive dysfunction. By age 53, he was severely disabled, requiring percutaneous gastrostomy for feeding. Anti-IgLON5 was negative. He fulfilled the clinical criteria for probable progressive supranuclear palsy. He died from pneumonia at age 54. The neuropathological examination revealed a 4-repeat tauopathy with features of CBD with extensive involvement of the brainstem.

RP-CBD may resemble brainstem encephalitis. The severity of brainstem and upper spinal cord pathology in the postmortem examination correlated with the clinical and imaging features.