19 Feb - Progressive Multifocal Leukoencephalopathy

     An elderly male with a long history of HIV disease presents with a rapidly progressing dementing illness associated with visaul loss.  His MRI revealed extensive disease predominantly in the white matter but also involving gray matter.  The differential of CNS lesions in AIDS patients is broad, but most cases are attributable to lymphoma, toxoplasmosis, PML, cryptococcus, and rarely (in the US) TB.  In this case CSF was remarkable for high protein and 2 WBCs.  This is a typical bland CSF appearance for PML.  PCR for JC virus was positive.
     PML is a rapidly progressive demyelinating disease caused by the JC polyoma virus that is usually fatal.  Most cases are associated with AIDS, however cases have been reported in patients recieving natalizumab for treatment of MS.  There is no treatment (other than retroviral drugs to treat HIV disease).
     The other major human disease caused a polyomavirus is the BK virus induced nephropathy in kidney transplant patients. 
     Remember the most up to date management strategy for differentiating toxoplasmosis from lymphoma is to perform Thallium 201 SPECT with early brain biopsy for lesions suspicious for lymphoma.  The old strategy of treat for toxo for 2 weeks and biopsy those that do not improve is not as favored given the peformance of SPECT.