ETosis-derived DNA trap production in middle ear effusion is a common feature of eosinophilic otitis media

Eosinophilic otitis media (EOM) is a recently recognized intractable middle ear disease in Japan and has been focused on in Western country.1 EOM is characterized by the strong infiltration of eosinophils in highly viscous ear effusion (eosinophilic mucin) and in the middle ear mucosa.2,3 Unlike conventional chronic otitis media, EOM is generally resistant to all pharmacological therapies except for systemic steroid treatment. Surgical techniques are often warranted to improve the drainage pathway so as to remove obstructive eosinophilic mucin. Patients with EOM have a high risk of conductive hearing loss in the early stage, and half of all patients develop an increased bone-conduction threshold, leading to deafness in 6% of cases.2,4 The high levels of toxic eosinophil granule proteins observed in the eosinophilic mucin are suggested to be pathogenic and to cause epithelial damage.4 Eosinophil degranulation is mediated by several mechanisms, namely exocytosis, piecemeal degranulation, and cytolysis. Cytolysis is a well recognized pathology in diverse eosinophil-associated diseases, including EOM,4 and was suggested to represent a full activation of eosinophils,5 although its precise mechanism is not understood. A recent finding showed that extracellular trap cell death (ETosis), a novel form of cell death, mediates eosinophil cytolytic degranulation.6 Eosinophil ETosis (EETosis) is characterized by its striking final morphology: the release of intact granules and web-like chromatin structures (DNA traps/extracellular traps: ETs) through the breakdown of nuclear and plasma membranes. It does not feature apoptotic signatures such as phosphatidylserine exposure on the cell surface and DNA fragmentation. We have previously reported the presence of eosinophil ETs (EETs) in the middle ear secretions obtained from a few EOM patients.7 To clarify whether the presence of cytolysis and ETs is common in EOM, we conducted a case series study. All patients met the diagnostic criteria of Iino et al.2 and were seen by experienced ENT doctors at Yamagata City Hospital Saiseikan, Yamagata University Faculty of Medicine, and Tohoku Medical and Pharmaceutical University between February 2010 and August 2017. Informed consent was obtained under protocols approved by the Institutional Review Board. Clinical features of the patients with EOM are summarized in Table 1. The patients were 4 men and 4 women who ranged in age from 25 to 72 years. Audiometry was performed by audiologists using a pure-tone audiometer (AA-76, Rion, Tokyo, Japan). All patients had comorbid chronic