IgG4-related lung disease as a differential diagnosis of a lymphoproliferative disease: atypical presentation of an atypical disease.

IgG4-related disease (IgG4-RD) is an immunomodulated inflammatory disease that usually affects the pancreas and parotid glands. Although lung involvement is rare, it has been recently reported and could mimic various other diagnoses. We present a case of IgG4-RD whose symptoms and images raised the suspicion of a malignant lymphoproliferative lung neoplasm. It is imperative to differentiate both diseases, since their treatment and prognosis vary.