Evaluation of the respiratory function in myasthenia gravis. An important tool for clinical feature and diagnosis of the disease.

Myasthenic gravis may affect both inspiratory and expiratory muscles. Respiratory involvement occurred in almost all patients with myasthenia gravis in all clinical forms of the disease: 332 lung function tests done in 324 myasthenic patients without respiratory symptoms (age 34.6 +/- 18.3 years) were examined. Lung volumes analysis showed that all the patients of both sexes with generalized or ocular myasthenia gravis showed "myasthenic pattern". Male patients with "ocular" form only presented the "myasthenic pattern" with lung impairment and had, from the lung function point of view, a more benign behaviour. Female patients with the "ocular" form exhibited a behaviour of respiratory variables similar to that of the generalized form. It was not observed modification of the variables that suggested obstruction of the higher airways. The "myasthenic pattern" was rarely observed in other neuromuscular diseases, except in patients with laryngeal stenosis.