A study of diagnostic yield, technical ease and patient discomfort of low rate repetitive nerve stimulation test in patients with myasthenia gravis.
OBJECTIVE
The diagnostic yield of repetitive nerve stimulation (RNS) study in different muscles has been evaluated in myasthenia gravis (MG) but there is paucity of comprehensive study on technical ease and patient comfort. In this study we evaluate diagnostic yield of RNS test, technical ease and patient discomfort in 8 different muscles in patients with MG.


METHODS
Consecutive patients with MG diagnosed on the basis of clinical evaluation, neostigmine test and/or acetylcholine receptor antibody (AchRAb) assay were subjected to 3 Hz RNS study in abductor digiti minimi (ADM), flexor carpi ulnaris (FCU), anconeus, deltoid, trapezius, serratus anterior (SA), nasalis and tibialis anterior (TA) at rest and 3 min after 30 s exercise. Decrement exceeding 10% was considered abnormal. Patient's discomfort was assessed on a 0-5 scale and technical difficulty by the number of repetitions needed to complete the test or abandonment of test.


RESULTS
Thirty-three patients with MG whose age ranged between 16-81 y were evaluated. At the time of RNS study the predominant weakness was ocular in 3, oculobulbar in 13 and limb in 17 patients. The highest diagnostic yield of RNS test was with deltoid and nasalis (78.8% each), followed by trapezius (65.5%). The highest mean patient discomfort score was with deltoid (2.4), followed by nasalis (1.3). The technical difficulty was maximal in deltoid needing 36.4% repetitions followed by SA (33.3%). In oculobulbar group the best yield was in nasalis (92.3%) followed by deltoid (84.6%), and in limb variety deltoid (82.4%) followed by SA (80%) and trapezius (75%). Combining the diagnostic yield, patient comfort and technical ease; the choice of muscle for RNS should be ADM followed by trapezius for patient with predominant limb weakness, nasalis and trapezius in oculobulbar and nasalis in ocular.
Misra
U K
UK
Department of Neurology, Sanjay Gandhi PGIMS, Lucknow. ukmisra@sgpgi.ac.in
Kalita
J
J
Srivastava
A
A
D000200:Action Potentials / Q000502:physiology; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004558:Electric Stimulation / Q000009:adverse effects*; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation* / Q000503:physiopathology; D009157:Myasthenia Gravis / Q000175:diagnosis* / Q000503:physiopathology; D010146:Pain / Q000209:etiology*; D012146:Rest / Q000502:physiology; D012680:Sensitivity and Specificity