Spontaneous Haemopneumothorax in a Young Female: A Case Report of Birt–Hogg–Dubé Syndrome

Birt–Hogg–Dubé syndrome (BHDS), also known as Hornstein–Knickenburg syndrome, is a rare autosomal dominant disorder caused by mutations in the FLCN gene, characterised by cutaneous lesions, pulmonary cysts, spontaneous pneumothoraces, and renal tumours. The authors report a case of a 23-year-old, previously healthy female who presented with acute left-sided chest pain and was diagnosed with spontaneous haemopneumothorax. Imaging revealed a hydropneumothorax with complete left lung collapse and a breast mass, later confirmed as a fibroadenoma. She also exhibited skeletal features and mitral valve prolapse, raising suspicion of Marfan syndrome, which was excluded through genetic testing. Instead, a pathogenic FLCN mutation (c.1285del, p.His429ThrfsTer39) confirmed BHDS. No renal abnormalities were identified on MRI. This case highlights the diagnostic challenges of BHDS, particularly in the absence of family history or overt cutaneous signs. Prompt recognition and genetic confirmation are crucial for appropriate management and surveillance of associated complications, including renal malignancies and recurrent pneumothoraces.