Office investigations for myasthenia gravis: comparative analysis

Abstract

The purpose was to study the diagnostic yield of the various tests including lid fatigue test, Cogan twitch, Rest test, Ice test and Repetitive nerve stimulation (RNS) study in clinically diagnosed myasthenic patients. A prospective study of newly diagnosed myasthenic patients was done at tertiary eye - care centre. Totally, 58 patients underwent tests for the confirmation of myasthenia gravis. Fishers Exact test was used for comparative analysis. Average age of presentation was 44.13 years. Number of male and female were 33 (56.9%) and 25 (43.1%). 8 (13.8%) patients were under the age of 15 years. Variability was observed in 47/58 (81.04%) patients and Fatigue was seen in 40 /58(68.97%) patients. Cogan twitch was observed in 28/58(48.28%) patients. Sensitivity of Rest test was 50%. Sensitivity of Ice test was 72.4%. Ice test positivity was 90% (9/10) in mild, 75% (21/28) in moderate, 68.75% (11/16) in severe ptosis indicating that increasing severity decreases the sensitivity. Sensitivity of combined Rest test and ice test was 90 %. Sensitivity of RNS study was 90%. The difference between the RNS study and Ice test was not statistically significant (p- 0.583). However RNS study showed higher percentage of positivity. Ice test is more sensitive than rest test. Rest test and Ice test are simple, cost benefit bed side tests when combined, have sensitivity equivalent to RNS study. However RNS study is the gold standard confirmatory test.