[Electrodiagnostic assessment of neuromuscular junction disorders]

Electrodiagnosis of neuromuscular junction disorders relies on repetitive nerve stimulation tests (RS) and single-fiber EMG (SFEMG). RS tests are usually performed on proximal and distal nerves (axillary, accessory, radial, facial, ulnar, median, peroneal). Ischemic test substantially improves ulnar RS sensitivity. More recently RS of masseter and hypoglossal nerves have been proposed to increase RS sensitivity in patients with bulbar symptoms in myasthenia gravis (MG). RS of phrenic and long thoracic nerves could be used in MG patients with respiratory symptoms. Sensitivities of these tests are widely different but they are complementary. SFEMG is far more sensitive but technical difficulties have limited its use. In generalized MG, RS should be performed first. Clinically involved muscles should be examined first, then other muscles. If RS tests are negative, SFEMG of facial muscles can be used. In ocular MG, SFEMG, if available, is the best option. In Lambert-Eaton myasthenic syndrome, a single shock on ulnar nerve before and after a brief maximum voluntary contraction should be used to demonstrate increment and 3 Hz RS a decrement. If negative, median and radial nerves should be studied. Additionally electrodiagnosis features of congenital myasthenic syndromes and botulism are reviewed.