Birt-Hogg-Dubé syndrome: a hidden genetic cause of recurrent pneumothorax in a non-smoker.

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant disorder characterised by pulmonary cysts, recurrent spontaneous pneumothorax, cutaneous lesions and an increased risk of renal tumours. Pulmonary manifestations often precede other features, leading to delayed recognition. We report the case of a non-smoking male in his early 60s who presented with recurrent left-sided spontaneous pneumothorax and exertional dyspnoea. Cutaneous examination revealed multiple acrochordons over the neck. Chest imaging demonstrated pneumothorax, and high-resolution CT of the thorax showed a left upper lobe bulla with multiple bilateral thin-walled pulmonary cysts with basal predominance. The patient underwent bullectomy and surgical pleurodesis. Histopathology revealed thin-walled cysts lined by normal respiratory epithelium without smooth muscle proliferation, and HMB-45 immunostaining was negative, excluding lymphangioleiomyomatosis. Serum alpha-1 antitrypsin levels were normal. Genetic analysis identified a heterozygous pathogenic frameshift variant (c.1285delC) in the FLCN gene, confirming the diagnosis of BHD syndrome. The postoperative course was uneventful, and renal surveillance and family counselling were initiated. This case underscores the importance of considering BHD syndrome in non-smokers presenting with recurrent pneumothorax and cystic lung disease, as early diagnosis facilitates appropriate surveillance and genetic evaluation.