A middle-aged man presenting with unexplained mucosal erosions and progressive dyspnoea.

Paraneoplastic pemphigus (PNP) is a rare syndrome driven by antibodies (IgG) binding to desmogleins and other epidermal proteins leading to skin erosions. In rare instances, these same IgG proteins may also target the bronchial mucosa leading to an irreversible fibrotic reaction within the epithelium and subsequent obstructive lung disease. A 51-year-old man presented to the emergency department with 2-3-month history of dyspnoea as well as oral and genital ulcerations and inguinal lymphadenopathy. The ulcerations were biopsied and proven to be consistent with pemphigus. Subsequent inguinal lymph node biopsy implicated the hyaline-vascular variant of Castleman's disease (CD), as the primary cause of the patient's pemphigus. The patient underwent pulmonary function testing that demonstrated severe airflow obstruction. The patient was diagnosed with PNP and associated bronchiolitis obliterans syndrome (BOS). He was treated with rituximab for his CD, and oral and inhaled corticosteroids along with azithromycin for his BOS.