Ultrasound has emerged as a useful tool in diagnosing carpal tunnel syndrome and has been shown to have a sensitivity of 87% and specificity of 83% on a recent meta-analysis examining 38 studies (3995 wrists) that established diagnostic criteria (Tai et al.). To reduce interindividual variability, the nerve is measured at 2 points in the wrist, at both the tunnel inlet and quadratus pronator, with the difference measured between each point (Klauser et al.; Roll et al.; Tajika et al.).

In a study by Moran et al., 73 patients (105 hands) with a clinical suspicion of carpal tunnel syndrome were studied with ultrasound. All patients had baseline electrodiagnostic testing in addition to ultrasound measurements of the cross-sectional area of the median nerve. A new advanced ultrasound measurement of nerve stiffness using shear wave elastography was also used to assess the nerve.

The authors found that both conventional ultrasound and quantitative ultrasound elastography were an alternative to electrodiagnostic testing in patients with a suspicion of carpal tunnel syndrome. The cross-sectional area of the median nerve increased proportionally to the increase in carpal tunnel severity (as determined by baseline electrodiagnostic testing). The authors concluded that ‘[ultrasound] with elastography could replace [electrodiagnostic testing] in the workup of patients with a clinical suspicion of [carpal tunnel syndrome]” (Moran et al.).

References:

Atroshi I, Gummesson C, Johnsson R, Ornstein E. Diagnostic properties of nerve conduction tests in population-based carpal tunnel syndrome. BMC Musculoskelet Disord. 2003 May 7;4:9.

Klauser AS, Halpern EJ, De Zordo T, Feuchtner GM, Arora R, Gruber J, Martinoli C, Löscher WN. Carpal tunnel syndrome assessment with US:
value of additional cross-sectional area measurements of the median nerve in patients versus healthy volunteers. Radiology. 2009 Jan;250(1):171-7.

Moran L, Royuela A, de Vargas AP, Lopez A, Cepeda Y, Martinelli G. Carpal Tunnel Syndrome: Diagnostic Usefulness of Ultrasound Measurement of the Median Nerve Area and Quantitative Elastographic Measurement of the Median Nerve Stiffness. J Ultrasound Med. 2020 Feb;39(2):331-339.

Roll SC, Evans KD, Li X, Freimer M, Sommerich CM. Screening for carpal tunnel syndrome using sonography. J Ultrasound Med. 2011 Dec;30(12):1657-67.

Tai TW, Wu CY, Su FC, Chern TC, Jou IM. Ultrasonography for diagnosing carpal tunnel syndrome: a meta-analysis of diagnostic test accuracy. Ultrasound Med Biol. 2012 Jul;38(7):1121-8.

Tajika T, Kobayashi T, Yamamoto A, Kaneko T, Takagishi K. Diagnostic utility of sonography and correlation between sonographic and clinical findings in patients with carpal tunnel syndrome. J Ultrasound Med. 2013 Nov;32(11):1987-93.

Witt JC, Hentz JG, Stevens JC. Carpal tunnel syndrome with normal nerve conduction studies. Muscle Nerve. 2004 Apr;29(4):515-22.