Progressive systemic sclerosis (PSS) combined with the features of other connective tissue diseases such as systemic lupus erythematosus (SLE), dermatomyositis, and polymyositis (PM) has been referred to as overlap syndrome. A 12-year old girl presented with thickening of the skin on the face and hands, sclerodactylia, and Raynaud's phenomenon. Antinuclear antibodies (ANA) and topoisomerase-1 (anti-Scl-70) antibodies were found to be positive, and megacapillaries were observed by the nailfold capillarioscopy. The patient was diagnosed as PSS. The patient developed acute respiratory failure during her first hospitalization. Electromyography showed diffuse myogenic involvement. For severe clinical findings, intravenous (IV) cyclophosphamide (CP), prednisone and methotrexate treatment was started. The respiratory muscle involvement accompanied with skin findings, arthralgia, soft tissue contractures and subcutaneous calcifications suggested a PM-PSS association in the patient. At the 6th month of the therapy, renal biopsy was performed in the patient for the persisting microhematuria. The histopathological evaluation revealed mesangioproliferative glomerulonephritis with immune complex deposition. The anti-dsDNA, anti-SS-A (anti-Ro) and ENA (extractable nuclear antigen) antibodies became positive at the same period and the histopathological findings were described as Class II lupus nephritis. Six months after the first diagnosis of PSS and PM, the development of SLE findings suggested overlap syndrome consisting of PM-SLE-PSS, a very rare disease of childhood.

Keywords: overlap syndrome, lupus nephritis, progressive systemic sclerosis, polymyositis, overlap sendromu, lupus nefriti, ilerleyici sistemik skleroz, polimiyozit