Electrophysiological Predictors of Seropositive and Seronegative Myasthenia Gravis (P3.174)

OBJECTIVE: To determine the pattern of RNS decrement between seropositive and seronegative groups. BACKGROUND:Repetitive nerve stimulation and Antibody assessment are routinely performed investigations to confirm a diagnosis of Myasthenia gravis(MG). AchR antibodies are present in 80[percnt], MUSK antibody in 5-10[percnt] and 10-15[percnt] MG patients are double seronegative. DESIGN/METHODS: We conducted a retrospective chart review of MG patients from 2001 to 2014. We reviewed their serological status and RNS studies. Presence of AchR antibodies and MUSK antibody was considered as seropositive while absence of these antibodies was considered as seronegative. >10[percnt] decrement in amplitude in RNS study was considered positive for MG. SPSS 21® was used to organize, validate and analyze collected data. Paired Student9s t-tests were performed to detect significant differences between selected groups. RESULTS:We reviewed 225 patients with MG. 78[percnt] of patients were seropositive (75[percnt] AchR and 2[percnt] MUSK antibody) and 60[percnt] of patients had RNS decrements. RNS decrement was seen in 51[percnt] seropositive and 71[percnt] seronegative patients (P=0.06). Among RNS positive muscles, we had 9 seronegative and 20 seropositive muscles available to review. There was no significant difference found between area or amplitude decrement between seropositive and seronegative groups. A decrement in area was more likely compared to decrement in amplitude in seropositive patients after exercise (P<0.05), but not before exercise. In the seronegative group, a decrement in area was more likely compared to amplitude before and 3 minutes after exercise (p<0.05) but not immediately after exercise, 1 or 2 minutes after exercise. CONCLUSIONS:These findings suggest that a decrement in area is more sensitive compared to amplitude decrement after exercise in seropositive patients. In seronegative patients, an area decrement before and 3 minutes after exercise increase the sensitivity, this will need confirmation in additional cohorts. Study Supported by:none Disclosure: Dr. Gandhi has nothing to disclose. Dr. Velis has nothing to disclose. Dr. Salgado has received personal compensation in an editorial capacity from Belvoir Media Group. Dr. Galvez-Jimenez has received personal compensation for activities with GlaxoSmithKline and Allergan, Inc. as a speaker.