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Muscle atrophy and weakness occurs commonly in patients with systemic sclerosis, especially late in the course of the disease. However, profound proximal muscle weakness secondary to myositis is an infrequent finding.To determine the frequency and disease characteristics of patients with myositis in our cohort of systemic sclerosis patients.A retrospective case note review of the clinical course of all patients enrolled on the South Australian scleroderma register, a population-based register of 374 living and 234 deceased patients with systemic sclerosis, last updated to the end of December 2002.Twenty patients with myositis were identified, the majority with diffuse cutaneous systemic sclerosis and overlap syndromes. The calculated frequency of this complication was 3.3% in our population-based cohort. All patients suffered profound proximal muscle weakness complicated by functional impairment. Other clinical features included weakness of cervical musculature (15%), dyspnoea (10%) and dysphagia (10%). Creatine kinase level was elevated in 80% of the patients, with the mean peak creatine kinase level of 1129 U/L. When further investigations were undertaken, 80% of patients demonstrated myopathic changes on electromyography and 92% of patients were found to have histological findings characteristic of an inflammatory process. Positive antinuclear antibodies were identified in all patients, including two with anti-PM-Scl autoantibodies.Myositis is an infrequent clinical feature in patients with systemic sclerosis. Profound proximal weakness in association with elevated creatine kinase levels and myopathic changes on electromyography should alert the clinician to this complication. The presence of anti-PM-Scl autoantibodies in association with overlap syndromes may have a more favourable prognostic significance.