Lessons for the clinical nephrologist: an uncommon cause of pulmonary-renal syndrome.

Pulmonary-renal syndrome refers to the combination of elevated plasma creatinine concentration and/or abnormal urinalysis with diffuse alveolar hemorrhage, and involves both an urgent diagnostic approach and care. We report the case of a 24-year-old man presenting with diffuse alveolar hemorrhage as well as a nephritic syndrome associating kidney failure, moderate hypertension, hematuria and selective glomerular proteinuria. The initial high suspicion of anti-glomerular basement membrane (GBM) disease or ANCA-associated vasculitis justified intravenous pulse-corticotherapy in association with plasma exchange. Renal biopsy was remarkable for an IgA nephropathy, lesions of active thrombotic microangiopathy (TMA) and a positive staining for complement factor C4d. Because anti-GBM and ANCA antibodies returned negative, plasma exchange was discontinued, but oral corticosteroids were maintained to prevent alveolar hemorrhage recurrence. In the absence of renal function recovery, hemodialysis was initiated. TMA lesions are frequently seen in IgA nephropathy and are associated with a poorer prognosis. Complement activation seems to be involved in the development of those lesions and contributes to disease progression. Conversely, alveolar hemorrhage in the setting of IgA nephropathy is uncommon. It is thought to result from non-specific mucosal hemorrhage, an immune complex mediated basement membrane damage and an IgA-mediated capillaritis against basement membrane antigens.