Introduction:

Microscopic polyangiitis (MPA) is part of the group of vasculitis associated with antineutrophil cytoplasmic antibodies (ANCA), whose presence of antibodies against myeloperoxidase (MPO) is observed in most cases (70-95 %), likewise, the renal compromise portends higher rates of morbidity and mortality. However, coexistence with Systemic Lupus Erythematosus (SLE) is infrequent, and with greater emphasis on the older adult or late-onset variant of SLE (1).

Purpose:

Present a rare case of two autoimmune diseases, which has been reported as overlapping syndrome and provide useful information that allows expanding differential diagnoses.

Case report:

We present the case of a 76-year-old male patient with a history of progressive polyarthralgias in deteriorating general condition, with debut in acute confusional syndrome, drop in glomerular filtration rate, microhematuria and almost nephrotic proteinuria. At the initial evaluation anemia and severe thrombocytopenia were found, in the immune profile ANA 1/320, complement consumed; fulfilling criteria for SLE, ANCAs reactive specifically MPO ANCA (1/320) and suspected Rapidly Progressive Renal Insufficiency (PRRI). Given the clinical context, it was decided to start consecutive pulses of methylprednisolone followed by oral prednisolone, and cyclophosphamide was established as maintenance therapy. Finally, a renal biopsy confirmed the diagnosis of pauci-immune systemic vasculitis with cell crescent formation. These findings were consistent with both SLE and PAM, thus it was diagnosed as a case of overlap. The clinical evolution of the patient was satisfactory, achieving organ stabilization and normalization of renal function, hematopoietic function, and neurological status.

Discussion and conclusion:

RPGN associated with ANCA present non-nephrotic proteinuria, glomerular filtration rate drop. The most common is anti-glomerular basement membrane (AMBG) antibodies. Serological detection of antineutrophil cytoplasmic antibodies, PR3 and MPO should be available. Microscopic polyangiitis could be determined by renal biopsy, with the presence of cell growth, absence of immune deposits and MPO ANCA positivity. This case is a diagnostic enigma, and the complexity in the management of rare entities, of immunological etiology, superimposed that endanger the life of those who suffer from it, if they do not have a timely diagnosis and early treatment.

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