Microscopic polyangiitis in pediatric systemic lupus erythematosus: a unique presentation of pulmonary-renal syndrome and case report of an overlap syndrome.

Secondary vasculitis is encountered in about one-third of all cases of systemic lupus erythematosus (SLE). Skin is most commonly involved in lupus-related small vasculitis. Although antineutrophil cytoplasmic autoantibodies (ANCA) associated vasculitis (AAV) is relatively uncommon, it can be the most dangerous manifestation associated with high mortality. SLE and AAV are separate diseases with different pathophysiologies and an overlap syndrome has only been reported a few times in previous literature. We present a unique case of a pediatric patient of pulmonary-renal syndrome, presenting with pulmonary alveolar hemorrhage and rapidly progressive glomerulonephritis. Serological and biopsy findings were suggestive of SLE and AAV occurring, simultaneously. Renal biopsy demonstrated necrotizing and crescentic glomerulonephritis, superimposed on diffuse segmental proliferative lupus glomerulonephritis class IV. The presentations of autoimmune diseases and vasculitis can be multi-systemic. Considering overlap syndromes, especially in patients with underlying connective tissue disease or systemic vasculitis, is vital for prompt therapy and prevention of morbidity in this population.