ULTRASONOGRAPHIC DIAPHRAGM THICKNESS CORRELATES WITH COMPOUND MUSCLE ACTION POTENTIAL AMPLITUDE AND FORCED VITAL CAPACITY

Introduction: Noninvasive evaluation of respiratory function in patients with various neuromuscular disorders is important for predicting life expectancy. Methods: We performed B-mode ultrasonography (USG) and nerve conduction studies in 37 patients (16 had amyotrophic lateral sclerosis; 11, myopathy; and 10, neuropathy) and 10 controls. USG of the diaphragm was performed in the supine position using a linear probe over the intercostal space at the anterior axillary line. Diaphragm muscle thickness was measured at end-expiration. The amplitude of diaphragm compound muscle action potentials (CMAP) was obtained by phrenic nerve stimulation with a surface electrode. Respiratory function was measured with standard pulmonary function tests including forced vital capacity (FVC). Results: Diaphragm thickness was significantly correlated with FVC (r = 0.74) and CMAP amplitude (r = 0.53). Conclusions: Diaphragm USG is useful for objective evaluation of pulmonary function in neuromuscular disorders without requiring undue patient effort or cooperation.