Seasonal occurrence of nonepisodic angioedema with eosinophilia: A case series of 12 patients

Angioedema with eosinophilia is a rare condition characterized by marked eosinophilia and nonpitting edema. Nonepisodic angioedema with eosinophilia (NEAE) is more common in Japan than in other countries. This study analyzed 12 NEAE cases from Akita Prefecture and 70 cases from the literature to examine clinical features and seasonal patterns. In the Akita cases, patients were predominantly women (91.6%) and in their 20s to 30s. Edema mainly affected the lower legs and dorsum of the hands, with common symptoms, such as arthralgia (50%) and skin issues (50%). The mean eosinophil count was 4,678/µL, and most cases occurred from late summer to autumn. The literature review showed similar demographics to those of the Akita cases, and 87.1% of the patients were women in their 20s to 30s. Common symptoms included weight gain (37.1%) and arthralgia (37.1%), with a mean eosinophil count of 8,914/µL. Over half of the patients had onset between September and December. NEAE cases appeared more frequently during peak <i>Mycoplasma pneumoniae</i> infection outbreaks in Akita Prefecture, and both conditions tended to occur predominantly in autumn and winter, suggesting a possible association. These findings highlight a potential association between NEAE and <i>M. pneumoniae</i> infections, possibly through mechanisms such as molecular mimicry. Further large-scale studies are required to clarify NEAE's pathogenesis.