Diffuse aspiration bronchiolitis (DAB) is a chronic inflammatory response of the bronchioles caused by repeated aspiration of foreign bodies. It is common among older individuals with dysphagia associated with neurological diseases or dementia. Here, we present the case of a woman in her 40s who was presumed to have developed DAB due to neuromyelitis optica spectrum disorder (NMOSD). There have been no reports of DAB due to NMOSD. The absence of obvious episodes of aspiration and the fact that pneumonia was the predominant symptom delayed the diagnosis despite the appearance of specific neurological abnormalities. DAB caused by neurological diseases of the brainstem should be considered in younger patients with diffuse centrilobular opacities, even if dysphagia is not obvious.