EAF is a rare disorder that involves the upper respiratory tract, which is diagnosed on the basis of the characteristic pathological findings, as previously mentioned [1–3]. The histopathological diagnosis takes two possible disease progression states into consideration: an inflammatory state and a fibrotic state [4, 5]. It is considered that the disease progresses from the early-state inflammatory lesion, with numerous eosinophils and perivascular onion skin fibrosing to a late state characterized by subsequent perivascular fibrosis formation and decreased inflammatory infiltration. In our case, the resected specimen contained these metachronous states, with an early state predominance. The enhanced accumulation on FDG-PET reflected the inflammatory cell infiltration and indicated a high-activity lesion. EAF of the lung should be considered in the differential diagnosis of a hilar mass lesion with abnormal accumulation that mimics lung cancer.
The etiology of EAF is unknown; atopy, trauma, surgery, and immunologic disease have been proposed as predisposing factors, but none of these is supported by evidence [6, 7]. Deshpande et al. reported five cases of EAF and concluded that EAF belongs to a spectrum of IgG4-related disorders [4]. In their cases, numerous IgG4-positive plasma cells have been observed in EAF biopsy samples, together with elevated serum IgG4 levels [8]. Although our case showed similar pathological findings, other laboratory results did not concur. We did not reach the definite the diagnosis for IgG4-related disease.
The differential diagnosis of pulmonary EAF includes GPA and eosinophilic GPA (EGPA) [3, 9], both systemic diseases with lung involvement. The most important histopathological distinguishing features are necrosis and vasculitis, which are not observed in EAF in our case. In addition, our patient lacked the diagnostic clinical findings associated with GPA and EGPA [10, 11]. The only positive serum assay was p-ANCA, which are the autoantibodies observed characteristically in EGPA. However, they are observed only in half of the EGPA cases, and the criteria proposed by the American College of Rheumatology do not include p-ANCA [11]. Our patient had not any clinically associated presentation. Consequently, we did not reach the definite diagnosis for these diseases.
While EAF is a benign disorder that involves the upper respiratory tract and leads to airway obstruction, the obstructive symptoms develop gradually because EAF is slow growing and progressive. Kim et al. reported a case of EAF that occurred in the bronchial lumen of a patient who presented with respiratory distress [5]. Similarly, in our case, chronic cough appeared as a local manifestation and disappeared after surgical treatment. If bronchial narrowing had progressed, disorders such as obstructive pneumonia would have developed. The medical treatment of EAF is not established. Therefore, surgical treatment for symptomatic relief was required in most of the reported cases. Whenever surgical resection is deemed feasible, it is desirable to intervene before the obstruction becomes severe. Among the cases where surgical excision was performed, one recurrence was described following a non-total resection [3]. Even in the case of a pulmonary lesion, a total resection may be required, and we therefore insist on the confirmation of the surgical margin by intraoperative rapid diagnosis.
In our case, EAF was not associated with a co-existing systemic disease. As previously described, EAF is an inflammatory disorder of uncertain origin. However, it is not known if EAF is a partial manifestation of a systemic illness, which highlights the importance of performing an adequate evaluation. As reported by Rimmer et al. [12], the possibility of advancing toward the development of these diseases is an important concern. Careful follow-up after surgery is also important.
