Correlation of Respiratory Function Tests With Repetitive Stimulation of Long Thoracic Nerve in Myasthenia Gravis

Objective: Myasthenia gravis (MG) is an autoimmune disease. Respiratory weakness and bulbar involvement are the major complications and early diagnosis of these complications is very important for the planning of treatment. Method and Patients: Twenty-one patients with myasthenia gravis and 21 healthy controls were included in this study. Repetitive nerve stimulation (3Hz) tests were performed on facial, ulnar and long thoracic nerves. The difference between the first and fourth compound muscle action potential (CMAP) amplitudes was recorded. Respiratory functions were evaluated using forced vital capacity (FVC) and the ratio of forced expiratory volume in 1s (FEV1) to FVC. Results: 15 male and 6 female patients were included in the patient group. The sensitivity and specificity of long thoracic nerve compared to facial nerve were 0.86 and 0.66, respectively. There was a significant difference between the decrements recorded from serratus anterior (SA). A strong correlation was observed between the percentage of the decrement recorded from SA and FEV1/FVC ratio. Conclusions: The use of repetitive stimulation of long thoracic nerve compared to respiratory function tests might be a well-tolerated and simple way for the early diagnosis of pulmonary dysfunction in MG. Significance: This well-tolerated method should be recommended in routine electromyography protocols.