Muscle ultrastructure in a case of mixed connective tissue disease and Sjögren's syndrome

A 29-year-old black woman with clinical and serological diagnoses of Sjörgren's Syndrome (SS) and mixed connective tissue disease (MCTD) presented a very important muscular compromise with proximal, bilateral weakness and wasting, an abnormal electromyogram, and elevated muscle enzymes. Ultrastructural study of a muscle biopsy showed different degrees of atrophy and presence of subsarcolemmal loss of sarcomeric arrangement forming regions of contractil material with diverse electron densities. Capillaries were proliferative with distortion or occlusion of lumen and thickened basement membranes. An unusual capillary abnormality consisting of thick and convoluted basement membrane intermingled with portions of endothelium and macrophages is described. Mononuclear cell infiltration was formed by lymphocytes, plasma cells, macrophages and scarce mast cells. This work is the first study of the ultrastructural muscle pathology in a patient with diagnoses of MCTD and SS based on clinical findings and the presence of antibodies to RNP, SS-A and SS-B antigens.