Quantitative Change of Repetitive Nerve StimulationTest in Myasthenia Gravis

ABSTRACT

Repetitive nerve stimulation test (RNS) is an easy and non-invasive test which provides objective for the presence of a myasthenic neuromuscular defect and for monitoring possible improvement through various therapeutic measures, and makes the differentiation of neuromuscular junction disorders. Analysing the RNS test of 45 normal controls and 146 patients with myasthenia gravis quantitatively, the following results obtained. 1. At low rate stimulation, the decremental response upto 2 standard deviation in normal control are 7.1% in orbicularis oculi(~), 7.6% in flexor carpi ulnaris (FCU) and 5.4% in abductor digiti guinti muscle(ADQ). There are two kinds of facilitation noticed incremental responses at repetitive low stimulation (13.3-14.9%) immediately after tetanic stimulationy and increased mean amplitudes of compound muscle action potentials after exercise(l3-17%). Four minutes after the tetanic stimulation, the decremental responses at low rate stimulation become accentuated slightly even in normal control group. 2. At low rate stimulation. There are singificant decremental decremental responses in patients with myasthenia gravis, but statistically no significant differences are seen in the quantity of decremental responses among 2, 3 and 5/sec rate of stimulation. 3. The pattern and severity of decremental responses at low rate stimulation are depending on the clinical type of generalized myasthenia gravis. There are no decremental responses in FCU or ADQ in ocular type. The decremental responses of oo are greater than that of FCU in mild generalize myasthenia, but the reverse is true in moderate generalized type. 4. Statistically significant post-tetanic facilitation and exhaustion are noticed in patients with generalized myasthenia gravis.