RECOMMENDATIONS REGARDING EDX STUDIES TO CONFIRM A CLINICAL DIAGNOSIS OF CTS
The recommendations below are identical to those made and endorsed in 1993 by the American Academy of Neurology, the American Academy of Physical Medicine and Rehabilitation, and the American Association of Electrodiagnostic Medicine.
In patients suspected of CTS, the following EDX studies are recommended:
- Perform a median sensory NCS across the wrist with a conduction distance of 13 cm to 14 cm. If the result is abnormal, comparison of the result of the median sensory NCS to the result of a sensory NCS of one other adjacent sensory nerve in the symptomatic limb.
- If the initial median sensory NCS across the wrist has a conduction distance greater than 8 cm and the result is normal, one of the following additional studies is recommended:
comparison of median sensory or mixed nerve conduction across the wrist over a short (7 cm to 8 cm) conduction distance with ulnar sensory nerve conduction across the wrist over the same short (7 cm to 8 cm) conduction distance, or comparison of median sensory conduction across the wrist with radial or ulnar sensory conduction across the wrist in the same limb, or
comparison of median sensory or mixed nerve conduction through the carpal tunnel to sensory or mixed NCSs of proximal (fore arm) or distal (digit) segments of the median nerve in the same limb.
- Motor NCS of the median nerve recording from the thenar muscle and of one other nerve in the symptomatic limb to include measurement of distal latency.
- Supplementary NCS: comparison of the median motor nerve distal latency (second lumbrical) to the ulnar motor nerve distal latency (second interossei); median motor terminal latency index; median motor nerve conduction between wrist and palm; median motor nerve compound muscle action potential (CMAP) wrist-to-palm amplitude ratio to detect conduction block; median sensory nerve action potential (SNAP) wrist-to-palm amplitude ratio to detect conduction block; short segment (1 cm) incremental median sensory nerve conduction across the carpal tunnel (Option).
- Needle electromyography (EMG) of a sample of muscles innervated by the C5 to T1 spinal roots, including a thenar muscle innervated by the median nerve of the symptomatic limb (Option).
Based on the second AAEM CTS Literature Review, the following EDX studies are not recommended to confirm a clinical diagnosis of CTS either because the EDX studies recommended above have greater sensitivity and specificity or the test is best described as investigational at this time.
- Low sensitivity and specificity compared to other EDX studies: multiple median F-wave parameters, median motor nerve residual latency, and sympathetic skin response.
- Investigational studies: evaluation of the effect on median NCS of limb ischemia, dynamic hand exercises, and brief or sustained wrist positioning.