Unilateral Diffuse Alveolar Hemorrhage as an Initial Presentation of Microscopic Polyangiitis.

Diffuse alveolar hemorrhage (DAH) is a life-threatening condition due to widespread damage to small pulmonary vessels commonly caused by systemic vasculitis. Alveolar involvement is typically multi-lobar and bilateral. It frequently presents as bilateral diffuse airspace opacities on chest imaging. Unilateral DAH is rare. Patients presenting with hemoptysis, anemia, hypoxemia, progressive dyspnea, and opacities on chest imaging should be evaluated for systemic vasculitis such as antineutrophilic cytoplasmic antibody (ANCA) vasculitis. We report the case of a 23-year-old female who presented with hemoptysis, severe dyspnea, hypoxemia, anemia, and oliguria. The laboratory exam results showed the patient to be p-ANCA positive, which suggests a diagnosis of microscopic polyangiitis. Chest X-ray showed unilateral airspace opacities, and DAH was confirmed by hemosiderin-laden macrophages on bronchoalveolar fluid histopathological examination. After treatment with plasmapheresis, intravenous methylprednisolone pulse, and cyclophosphamide, the patient's symptoms and radiographic findings improved.