Clinical Relevance: Entrapment of the Median nerve at the wrist (Carpal Tunnel Syndrome) is the most common reason for electrodiagnostic referral. Despite this, the diagnosis of Carpal Tunnel Syndrome remains challenging due to the large number of electrodiagnostic test methods that have been developed.
This situation creates a dilemma for both referring and testing physicians. The referring clinician often lacks the in-depth knowledge of which test, or panel of tests, provide the best combination of sensitivity and specificity, compromising their ability to “over-read” the report and data with confidence. The testing physician is faced with choosing between this myriad of tests in a way that is both cost and time efficient without sacrificing either sensitivity or specificity.
Study Design: Authors Basiri and Katriji performed a review of the available published literature, as well as guidelines offered by the American Association of Electrodiagnostic Medicine and the Practice Parameter for Electrodiagnostic Studies in Carpal Tunnel Syndrome. This resulted in their recommendation of an algorithmic approach to EDX that is felt to be pragmatic, efficient, and clinically accurate. A diagrammatic overview to this algorithm can be found HERE.
Some additional interesting points from this article are:
- The most common site of sensory symptoms is in ALL digits, followed by the Median digits only, or a glove distribution.
- Absence of any symptoms in either the thumb, index, or middle finger makes the diagnosis of Carpal Tunnel Syndrome highly unlikely, regardless of the results on EDX testing.
- The best documented tests for diagnosing CTS (not all are required in every situation) are: distal median motor and sensory latencies, comparisons between median and ulnar sensory latencies between the wrist and palm, comparisons of median to ulnar sensory latencies to the ring finger, and comparison of median to radial sensory latencies to the thumb.
- The test with the highest reported sensitivity (97.5%) is comparing motor latencies while recording over the second lumbrical (for the Median nerve) to that of recording over the second interosseous (Ulnar nerve).
- Other commonly used studies are the Median-Ulnar comparative latency recording over the fourth finger (82% sensitive) and the Median-Radial comparative latency, recording over the thumb (60-69% sensitive).
This is an excellent article for anyone performing EDX testing, as well as for those who refer for such testing and desire a better understanding of the data they receive.
Please click the link for access to the full article: Practical approach to electrodiagnosis of the carpal tunnel syndrome: A review