Maximal respiratory pressures in myasthenia gravis. Relation to single fiber electromyography.

OBJECTIVES: The respiratory muscle weakness was evaluated in mild forms of myasthenia gravis (MG) and was compared with single fiber electromyography results (SFEMG) in the extensor digitorum communis muscle. MATERIAL AND METHODS: We assessed 61 treated MG patients without clinical respiratory involvement (13 ocular forms, 28 form IIa and 20 form IIb patients) by maximal respiratory pressure (MRP) to ascertain whether they were consistent with SFEMG results. RESULTS: Maximal expiratory pressure (MEP) and maximal inspiratory pressure (MIP) were reduced below the lower limit for healthy subjects in 85% and 77% of ocular patients; in 93% and 89% of form IIa, respectively; and in 95% of form IIb. The highest percentage of MEP and MIP reduction showed a positive correlation with increased jitter (r=0.45, P<0.001; r=0.27; P<0.05 respectively) and impulse blocking (r=0.35, P<0.01; r=0.28, P<0.05 respectively). CONCLUSION: We consider MRP measure useful for assessing respiratory muscle weakness in MG patients with subclinical respiratory involvement.