[An autopsy case of non-drug related progressive multifocal leukoencephalopathy in a background of rheumatoid arthritis].

A 56-year-old male subject was presented with a two-month history of dysarthria and gait disturbance. T₂-weighted MRI revealed high signal intensity in the right cerebellar hemisphere, pons, and bilateral middle cerebellar peduncles. Suspecting brain-stem encephalitis, he was treated with steroid pulse therapy, which was ineffective. Subsequently, a qualitative PCR test was performed, confirming the diagnosis of progressive multifocal leukoencephalopathy (PML) with a high JC virus (JCV) load (273,857 copies/ml) in the cerebrospinal fluid (CSF). The JCV strain in the CSF was a prototype with a deletion in the regulatory region of its genomic DNA. Long-term untreated rheumatoid arthritis (RA) was identified as an underlying cause. Other potential immunodeficiency-related diseases, including idiopathic CD4 lymphocytopenia, malignant RA, systemic lupus erythematosus, chronic eosinophilic leukemia, malignant lymphoma, and congenital immunodeficiency, were ruled out based on various laboratory tests. Despite treatment with a combination of mefloquine and mirtazapine, the patient died on the 102nd day due to disease progression. RA with non-drug related immune abnormalities should be considered a potential underlying cause of PML.