Isolated bilateral diaphragmatic paresis with interstitial lung disease. An unusual presentation of dermatomyositis.

A case of dermatomyositis (DM) with only one abnormal muscle function, bilateral diaphragmatic paresis, is reported. The coexistence of interstitial lung disease allowed us to sample the diaphragm during an open lung biopsy. Characteristic features of myositis were found. Lung volumes, compliance, maximal inspiratory pressure, and transdiaphragmatic pressure gradient (delta Pdi) were lower than normal. Lung recoil pressure was normal. Reversible small airways obstruction was also found. Treatment with prednisone produced dramatic improvement, with all functional values becoming normal except for compliance, which remained slightly decreased. A thorough evaluation of inspiratory muscle strength is advised in all patients with DM in order to identify varying degrees of altered diaphragmatic function.