[Sarcoidosis and progressive multifocal leukoencephalopathy].

A 70-year-old woman treated for sarcoidosis complained of progressive cognitive impairment and gait disability. Magnetic resonance imaging of the brain revealed a nonenhancing lesion in T1-weighted imaging in the left parieto-occipital region and sarcoidosis of the central nervous system was evoked. However, she rapidly deteriorated with posterior and cerebellar extension of the lesions, suggesting of progressive multifocal leukoencephalopathy (PML). DNA of the JC virus (JCV) was detected in the cerebrospinal fluid (CSF) by a polymerase chain reaction. Despite antiviral therapy, she died nine months after the first neurological signs. This case illustrates the possible association between sarcoidosis and PML, and underlines the interest to detect the presence of JCV in the CSF when the diagnosis of neurosarcoidosis appeared uncertain.