Oligodendrocytes wrap around nerves to produce myelin, a substance that protects nerves. Without protection, nerves quickly become dysfunctional. Small lesions may also form. Inactivated JCV is harbored in the kidneys, but when the immune system malfunctions, JCV somehow moves to the bone marrow. B lymphocytes transport JCV to the brain from bone marrow.
Symptoms usually progress rapidly.
Prognosis following diagnosis is poor and mortality is likely within one year. Some studies indicate a mean survival of 4 months. Diagnosis Signs of PML include white matter lesions below the outer layer of the brain, both focal and diffuse. There is a focal loss of oligodendrocytes with remaining oligodendrocytes in surrounding areas exhibiting enlargement of the nucleus and nuclear inclusions. Some astrocytes within lesions become infected abortively and become enlarged taking on bizarre cellular manifestations.