- Nerve Entrapment
- it is difficult to determine which patients require preoperative EMG/NCS prior to carpal tunnel release;
- consider applying this study in any patient involved in litigation, who falls under worker's compensation, or has risk factors for secondary gain;
- not only does EMG/NCS allow for documentation of the disease, but it also allows for postoperative documentation of nerve function if needed;
- sensory latency:
- most important, most sensitive, & earliest indicator of CTS is prolonged sensory latency;
- sensory evoked response may show diminished amplitude & is often absent;
- sensory latencies of 1-2 ms are considered mild, where as latencies more than 6 ms are considered severe;
- distal motor latency:
- is prolonged, but is not as sensitive an indicator as sensory latency;
- motor latency abnormalities tend to occur later in course of dz;
- EMG may show loss of motor units & presence of denervation potentials in the thenar muscles;
- although these abnormalities are present before clinically evident muscular atrophy sets in, they usually occur after distal motor latency is prolonged;
- motor latencies of 1-2 ms are considered mild, where as latencies more than 6 ms are considered severe;
- median nerve conduction velocity:
- in carpal tunnel syndrome, the median nerve conductional velocity is reduced to less than 50 m/s;
- insertional activity: will be increased in CTS;
- Ulnar Nerve:
- EMG/NCS is incomplete unless ulnar nerve of same arm is also evaluated to r/o possibility of peripheral neuropathy;
- Post Operative Changes:
- there is an immediate increase in motor conduction velocity following release of the carpal tunnel;
- one week post op this value decreases to an intermediate value & then gradually returns to nl over the ensuing 8-12 wks;
- in the report by Senda, et al, the authors evaluated the postop EMG changes in patients undergoing endoscopic CTR;
- 26 patients with idiopathic CTS (37 hands) who were followed for at least 6 months after ECTR;
- classified into four groups:
- those with normal distal motor latency (DML) and sensory conduction velocity (SCV) - group A
- normal DML and abnormal SCV as group B
- those with an abnormal DML and normal SCV as group C
- those with abnormal DML and SCV as group D
- all but one of the hands were classified as group D on the basis of preop EMG evaluation, while one was classified as group C;
- mean preoperative obtainable DML and SCV values were 7.2 m and 27.3 m/s;
- postoperatively, 12 hands were in group A, 8 hands in group B, 2 hands in group C, and 15 hands in group D;
- mean DML and SCV values at final follow-up were 4.3 ms and 40.8 m/s, respectively;
- of the 25 hands with muscle atrophy before surgery, 6 hands were in group A, 5 hands were in group B, 1 hand was in group C, and 13 hands were in group D at final follow-up;
- Electromyographic evaluation after endoscopic carpal tunnel release in idiopathic carpal tunnel syndrome.
The surgical treatment of the carpal-tunnel syndrome correlated with preoperative nerve-conduction studies.
False positive electrodiagnostic tests in carpal tunnel syndrome.
The carpal tunnel syndrome: localization of conduction abnormalities within the distal segment of the median nerve.
Carpal tunnel decompression in spite of normal electromyography.
AAEE minimonograph #26: the electrodiagnosis of carpal tunnel syndrome.
Time course and predictors of median nerve conduction after carpal tunnel release
[Riche-Cannieu anastomosis and a paradoxical preservation of thenar muscles in carpal tunnel syndrome: a case report.]
Marinacci communication: an electrophysiological study.
Median nerve function in patients undergoing carpal tunnel release: pre- and post-op nerve conductions.