Vasomotor dysfunction in carpal tunnel syndrome.

Little attention has been paid to small-fiber dysfunction in carpal tunnel syndrome (CTS) although its symptoms are common. This study investigates vasomotor dysfunction, which is controlled by small nerve fibers, in patients with CTS compared with control subjects. Vasomotor function was quantified by measuring, with laser Doppler velocimetry, skin vasoconstriction induced by a eutectic mixture of local anesthetic (EMLA) cream over digit tips 3, 4, and 5. Hands with CTS (n = 32) compared with controls (n = 19) demonstrated significantly reduced vasoconstriction in digits 3 and 4, but not digit 5. A blood flow ratio (digit 3/5) of less than 0.73 identified CTS in 69% with 68% specificity. Testing for vasomotor dysfunction in CTS allows for more comprehensive neurophysiological testing, which is heavily biased towards large nerve fibers.