[Antineuronal autoantibody to a 40-kDa protein in a patient with cerebellar ataxia and breast cancer].

A 49-year-old woman was admitted to Utsunomiya Saiseikai hospital complaining of right breast swelling. There was half a year history of difficulty in walking. A diagnosis of breast cancer was made by biopsy. Neurological examination revealed scanning speech, nystagmus, intention tremor and ataxic gait, but brain CT scan and MRI showed neither metastatic, invasive lesions nor atrophy in the brain. Lumpectomy for breast cancer was performed. For immunocytochemical studies, the cytoplasm of neurons in sections of normal human cerebral cortex, cerebellum, spinal cord and dorsal root ganglia were stained by the patient's serum, but glial cells were not. Upon Western blot, the patient's serum reacted with a 40-kDa protein in extracts of both cerebrum and cerebellum obtained from normal rats. A diagnosis of paraneoplastic cerebellar degeneration (PCD) was made on the basis of clinical manifestations and detection of the antineuronal antibody. The antibody accompanying the breast cancer which stained neuronal cytoplasm and bound to a 40-kDa protein may be a subtype of antibody causing PCD.