Diffuse Alveolar Haemorrhage as a Rare Pulmonary Manifestation of Antisynthetase Syndrome: A Case Series.

Background: Diffuse alveolar haemorrhage (DAH) is a rare but potentially life-threatening pulmonary complication of systemic autoimmune diseases. Although interstitial lung disease (ILD) is a hallmark of antisynthetase syndrome (ASyS), DAH has been only exceptionally reported in this setting. Methods: We present two patients with ASyS who developed DAH confirmed by bronchoalveolar lavage. Results: The first case involved a 52-year-old woman initially diagnosed with rheumatoid arthritis, later reclassified as rheumatoid arthritis-ASyS overlap, who developed DAH in the context of progressive ILD. The second case concerned a 37-year-old man with newly diagnosed ASyS who presented with recurrent DAH early in the disease course. Both patients required high-dose corticosteroids, followed by escalation of immunosuppressive therapy with rituximab or mycophenolate mofetil, resulting in clinical and radiological improvement. These cases illustrate the diagnostic challenges posed by DAH in ASyS, particularly due to overlapping features with infection and ILD exacerbation. They also highlight the importance of early bronchoscopy and timely intensification of immunosuppression. Conclusions: Increased awareness of DAH as a rare manifestation of ASyS may facilitate earlier recognition and improve outcomes in patients presenting with acute respiratory deterioration, anaemia, or haemoptysis.