[Respiratory form mof myasthenia gravis]

Extraocular, facial, bulbar and intercostal muscles are frequently affected in juvenile myasthenia gravis, especially during exacerbations. Acetylcholine receptor antibodies are often present in the blood in this type of myasthenic syndrome.

A girl presented with an exertional dyspnea at the age of 13 years, that improved after rest. All investigations were negative, except for lung function tests that showed a restrictive pattern. The diagnosis of juvenile myasthenia gravis was finally made at the age of 15 years because of the recurrence of sudden exertional dyspnea and a history of subtle weakness on repetitive movement leading to poor suckling, together with vocal and occasional swallowing difficulties. Dyspnea immediately improved after intravenous injection of 1 mg neostigmine, but the response was transient. No acetylcholine receptor antibody was found and a search for thymoma proved negative. Ambenonium chloride (Mytelase) was effective on clinical exacerbations, but the only improved test after 9 months of treatment was the functional residual capacity.

Anticholinesterase drugs must be tried in patients who present exertional dyspnea without bronchopulmonary or cardiac disease on the presumption of myasthenia gravis even when ocular or bulbar manifestations are absent.