Background Carpal tunnel syndrome (CTS) is the most frequent neuropathy of all entrapment neuropathies in the general population. Rheumatoid arthritis (RA) is one of the disease generate secondary CTS. The pathophysiology of CTS of RA might be different from idiopathic CTS. RA is a disease that has the characteristics to generate inflammatory synovial proliferation of the joint and also tendon. Although inflammation of the wrist joint and synovial tissue of the flexor tendons can cause increased pressure in the carpal tunnel, there is a possibility that even RA patients without symptoms of CTS also have subclinical median nerve damage because of the synovial proliferation and inflammation.
Objectives The aim of this study was to assess and compare the stiffness of the median nerve measured by quantitative elastosonography between patients with RA without symptom of CTS and controls.
Methods Four hundred two hands in 201 patients with RA and 222 hands in controls were included. All participants were examined both wrists. Ultrasound (US) examination was performed by using a 5- to 18-MHz linear array transducer (HI VISION Ascendus$;$ HitachiAloka Medical,Tokyo, Japan). As a reference medium, an acoustic coupler (EZUTECPL1$;$ HitachiAloka Medical) with a standardized elasticity was attached to the transducer during the elastosonography. The inlet of the carpal tunnel at the scaphoidpisiform level and the proximal portion of the carpal tunnel inlet were scanned in a transverse plane. The crosssectional area (CSA) and the elasticity of the median nerve, which was measured as the acoustic coupler/median nerve strain ratio, were evaluated. The measurements were repeated two times, and the average strain ratio was used for analysis.
Results We analyzed 342 hands in 177 RA patients (139 female, mean age: 63.5±11.6 years) and 158 hands in 81 non-RA (68 female, mean age: 71.5±14 years) finally. There were no significant differences in the cross-sectional area of median nerve (left: 8.9 vs 8.7 mm2, p=0.91, right: 8.2 vs 8.4 mm2, p=0.62) or the circumference of median nerve (left: 13.1 vs 13.4 mm, p=0.41, right: 13.7 vs 13.7 mm, p=0.95) within carpal tunnel between RA group and non-RA group. Strain ratio within carpal tunnel in RA group was higher than that of non-RA group (left: 2.6 vs 2.1, p=0.002, right: 2.7 vs 2.2, p=0.003). There were no significant differences in the cross-sectional area of median nerve (left: 7.5 vs 8.1 mm2, p=0.07, right: 8.8 vs 8.3 mm2, p=0.6), the circumference of median nerve (left: 13.1 vs 13.5 mm, p=0.3, right: 13.7 vs 13.9 mm, p=0.71) and strain ratio (left: 2.1 vs 2.0, p=0.88, right: 2.3 vs 2.1, p=0.01) at the entrance of the carpal tunnel between RA group and non-RA group.
Conclusions Real-time Elastosonography showed the stiffness of the median nerve with RA patients without any symptoms of CTS was higher than controls. It suggests that inflammation of flexor tenosynovitis and wrist joint may generate fibrotic change of median nerve in patients with RA.
Miyamoto H, Halpern EJ, Kastlunger M, et al. Carpal tunnel syndrome: diagnosis by means of median nerve elasticity–improved diagnostic accuracy of US with sonoelastography. Radiology. 2014;270:481–6.
Disclosure of Interest None declared