Progressive Multifocal Leukoencephalopathy in patients without obvious immunosuppression

I recently received a case in consultation which turned out to be progressive multifocal leukoencephalopathy (PML). Reading the clinical history, it was not entirely clear what predisposed the patient to PML. It wasn't clear, that is, until my mentor (the illustrious BK DeMasters) referred me to a nine-year-old paper by Sarah Gheuens, Gerald Pierone, Patrick Peeters, and Igor J. Koralnik entitled Progressive Multifocal Leukoencephalopathy in individuals with minimal or occult immunosuppression (J Neurol Neurosurg Psychiatry 2010;81:247-254). In this series, hepatic cirrhosis -- which was what my patient had -- was among the more common conditions in PML patients with minimal immunosuppression. Other conditions that can be associated with PML in the minimally immunosuppressed are those with renal failure and idiopathic CD4+ lymphopenia,

The authors discuss the possible mechanisms for the development of PML in patients with hepatic cirrhosis:

"[H]epatic cirrhosis can lead to portal hypertension and hypersplenism, with subsequent leucopenia as white blood cells are sequestrated in the enlarged spleen. Furthermore, cirrhosis also leads to hypogammaglobulinemia... It is well known that cirrhotic patients have a higher risk of developing bacterial infections, and 30–50% of deaths among cirrhotic patients are directly caused by infections. Immune dysfunction in hepatic disease may be caused by altered cytokine production, impaired cellular immune response and vascular disturbances, which lead together to increased susceptibility to infections."