Central nervous system manifestation of IgG4-related disease.

IMPORTANCE: IgG4-related disease (IgG4-RD) is characterized by an inflammatory reaction rich in IgG4-positive plasma cells. Head and brain involvement is rare in IgG4-RD, and brain parenchyma involvement has never been reported. OBSERVATION: A man in his mid-50s with multiorgan IgG4-RD developed progressive spastic hemiparesis and dementia. Magnetic resonance imaging of the brain revealed several cortical and subcortical lesions. Pathologic findings in the brain were consistent with IgG4-related central nervous system involvement. The patient was treated with high-dose corticosteroids followed by rituximab, and his cognitive and motor functions improved significantly. CONCLUSIONS AND RELEVANCE: IgG4-RD should be considered in patients with unusual neurologic manifestations suggestive of autoimmune disease.