BACKGROUND: In systemic lupus erythematosus, certain laboratory tests and evidence from muscle biopsy specimens of lymphocytic vasculitis reflect disease activity. A study was designed to determine if such indices predict respiratory lesions, and in particular whether the presence of vasculitis in quadriceps muscle reflects respiratory muscle function. METHODS: Twenty seven 27 patients with systemic lupus erythematosus were studied, ten of whom were consecutive untreated patients and 17 having clinically active disease and being treated. They were prospectively evaluated on the basis of erythrocyte sedimentation rate, lymphocyte count, C3 degradation products, quadriceps muscle biopsy, spirometry, lung volumes, carbon monoxide transfer factor, and mouth pressure during a maximal sniff. RESULTS: Lung function test results were abnormal in 12 patients. Vital capacity was reduced in seven, carbon monoxide transfer factor capacity in five, and mouth pressure was low (< 70% predicted) in ten. Lymphocytic vasculitis was seen in the muscle biopsy specimens of ten patients. No correlation was found between laboratory tests and lung function or mouth pressure, or between the presence of lymphocytic vasculitis and mouth pressure. In untreated patients, those with lymphocytic vasculitis had lower spirometric values. CONCLUSIONS: In systemic lupus erythematosus, evidence from muscle biopsy specimens of lymphocytic vasculitis is not predictive of impaired inspiratory muscle function as measured by mouth pressure. In untreated patients there were relationships between some laboratory test results and respiratory function, but this was not the case for the whole group. In systemic lupus erythematosus, laboratory tests and evidence from muscle biopsy specimens of lymphocytic vasculitis are therefore unlikely to be helpful in the assessment of respiratory disease.
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