Unilateral Diffuse Alveolar Haemorrhage as an Atypical Presentation of PR3-ANCA-Associated Vasculitis: A Case Report

Diffuse alveolar haemorrhage (DAH) is a life-threatening pulmonary manifestation of small-vessel vasculitis, most commonly associated with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Unilateral DAH has been infrequently reported and may pose diagnostic challenges, as its radiological presentation can mimic pneumonia, pulmonary oedema, or localized haemorrhage. This atypical presentation may delay recognition of the underlying vasculitis and appropriate immunosuppressive therapy. We present a case of a woman in her thirties with previously diagnosed PR3-ANCA-associated vasculitis who presented with acute worsening of dyspnea (mMRC grade IV) and hemoptysis. Radiological assessments revealed extensive right-sided ground-glass opacities with areas of consolidation and minimal left lower lobe involvement. Bronchoscopy with sequential bronchoalveolar lavage (BAL) showed progressively haemorrhagic aliquots consistent with DAH. Laboratory investigations revealed anemia (Hb 7.1 mg/dL) and elevated serum creatinine (5.02 mg/dL). The patient developed type I respiratory failure requiring mechanical ventilation and hemodialysis. She was treated with pulse intravenous methylprednisolone followed by rituximab therapy, along with trimethoprim-sulfamethoxazole prophylaxis. The patient improved clinically, radiologically, and biochemically and was discharged on supplemental oxygen.