Anti-NMDAR encephalitis in a patient with possible IgG4-related hypertrophic pachymeningitis: a case report.

IgG4-related hypertrophic pachymeningitis (IgG4-HP) may coexist with autoimmune diseases, malignancies, or infectious diseases. We describe a case of a patient with both possible IgG4-HP and anti-N-methyl-D-aspartate receptor (NMDAR) disease. A 67-year-old woman was admitted to the emergency department due to persistent speech difficulties. An MRI scan of her brain showed diffuse T1-isointense contrast enhancement. High IgG4 concentrations were found in the serum and CSF, and NMDAR antibodies were detected in the CSF. A dura biopsy showed lymphoplasmacytic infiltration of IgG4-positive plasma cells. She was treated with intravenous corticosteroid therapy for five days but was referred to us again approximately one month later due to psychosis and behavioral changes. Corticosteroid therapy was started again, improving her condition. The implications of the coexistence of possible IgG4-HP and anti-NMDAR disease are unclear. An accurate diagnosis of both conditions is needed to avoid suboptimal control of the clinical course. Close collaboration between the involved professionals is warranted.