Comment on study by Perkins et al.

The results of the study by Perkins et al. (1) are surprising since it is usually possible to make an electrophysiological diagnosis of carpal tunnel syndrome (CTS) even in the presence of a peripheral neuropathy. It is not clear from the report whether they made an electrophysiological diagnosis of CTS in any of their cases.

When routine antidromic sensory nerve conduction studies are nondiagnostic median/ulnar palmar latencies at 8 cm, median/radial antidromic latencies to the thumb at the same distance or median/ulnar motor to lumbrical/second interosseous muscle (2) recordings at the same distance should be used. Segmental sensory nerve conduction studies can localize the slowing of a prolonged median antidromic latency to the carpal tunnel (3).

Perhaps the criteria used for the clinical diagnosis of CTS in diabetic patients with a peripheral neuropathy did not discriminate well. The sensory symptoms experienced by patients with CTS are quite varied (4), and the addition of a diabetic neuropathy can further obscure the picture. The study required any four of six criteria to make the diagnosis. Patients with a condition other than CTS, such as ulnar neuropathy, cervical radiculopathy, diffuse peripheral neuropathy, or even thoracic outlet syndrome, might have been included as having CTS. Since their patients may have hand paresthesias from neuropathy, do we need to rely on more specific symptoms such as nocturnal awakening, relief by shaking the hand, and aggravation by reading, driving, etc.? Thenar muscle weakness is a late sign and not helpful in most cases. Perhaps the CTS cases of Perkins et al. were mostly mild. Subclinical slowing of median nerve conduction at the wrist is very common in diabetic subjects, and it’s surprising that this did not show up in their data.

Repeating the study using one of the much more appropriate nerve conduction techniques listed above and with different clinical inclusion criteria would be of considerable interest.