Progressive Multifocal Leukoencephalopathy With Hyper-IgM Syndrome in a 6-Year-Old Boy.

Hyper-immunoglobulin (Ig) M syndrome is a congenital immunodeficiency disorder characterized by increased serum IgM with low serum IgG, IgA, and IgE. We report the case of a 6-year-old boy with hyper-IgM syndrome as an underlying disease who showed progressive multifocal leukoencephalopathy findings on brain magnetic resonance imaging after visiting the hospital due to left upper extremity muscle weakness, gait disturbance, and speech impairment. At the time of hospitalization, he was treated with steroids and intravenous immunoglobulin, and his condition improved somewhat, but 6 months later, he visited the hospital with rapid deterioration.