Pulmonary Nodular Lymphoid Hyperplasia in a Case of Overlapping Neuromyelitis Optica Spectrum Disorder and Myasthenia Gravis

ABSTRACT Background Anti‐aquaporin 4 (AQP4) antibody‐positive neuromyelitis optica spectrum disorder (NMOSD) is a neuroinflammatory autoimmune astrocytopathy. While the precise mechanism of autoantibody production has not been completely elucidated, most AQP4‐IgG is believed to originate in the peripheral lymphoid tissue. Case Presentation Herein, we present a rare case of overlapping anti‐AQP4 antibody‐positive NMOSD and anti‐acetylcholine receptor (anti‐AChR) antibody‐positive myasthenia gravis (MG), incidentally accompanied by pulmonary nodular lymphoid hyperplasia (NLH), a condition also observed in several cases with Sjögren's syndrome. Conclusions The present case suggests that NLH, which may have been overlooked, can be found in NMOSD and MG. Although NLH was not considered a source of pathological autoantibodies, further analysis is required to clarify whether NLH is involved in the pathogenesis of chronic inflammatory conditions.