IgG4 inflammatory pseudotumor mimicking primary lung cancer.

Introduction:IgG4 related disease (IgG4-RTD) is an infrequent disease with possible multiple organ involvement. It is characteristic to find inflammatory nodules with IgG4 positive plasma cell infiltration, storiform fibrosis and obliterative phlebitis. We present a patient with an inflammatory pseudotumor in the right upper lobe, mimicking a primary lung tumor. Case report:Our patient, a 48-year old heavy smoker (25 pack/year) with no relevant medical background, referred chest pain, non-productive cough and sporadic nightly fever. Image findings revealed a mass in the right upper lobe, with increased SUV in PET-scan, and mediastinal lymphadenopathies. Primary lung tumor was suspected and right upper lobectomy was performed. Due to absence of cellular atypia and the intense plasmacytic activity in the lesion, immunohistochemical analysis was performed: abundant IgG4 plasma cells were identified, with a IgG4/IgG relation of 74%. Diagnosis of IgG4- inflammatory pseudotumor was made. Discussion:After an extensive bibliographic review, we found just one similar case reported with an IgG4-lung pseudotumor without systemic disease.  Due to the broad spectrum of clinical features of IgG4-RTD, and the  potential multiple organ involvement, it is hard to find a classification and diagnostic criteria with high sensitivity and specificity, nevertheless they can be useful in clinical practice. Conclusion:There are several benign inflammatory diseases which can mimic a primary lung tumor. Although incidence is low, IgG4 pseudotumor should be considered as a differential diagnosis in the absence of malignancy.