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Electrodiagnosis for CTS

- See:
      - Electromyography
      - Nerve Entrapment

- Discussion:
    - 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.