Effect of Carpal Tunnel Syndrome on the Ulnar Nerve at the Wrist

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1 ORIGINAL RESEARCH Effect of Carpal Tunnel Syndrome on the Ulnar Nerve at the Wrist Sonographic and Electrophysiologic Studies Seok Kang, MD, Seung Nam Yang, MD, PhD, Joon Shik Yoon, MD, PhD, Hyo Jeong Kang, MD, Sun Jae Won, MD Received February 25, 2015, from the Department of Physical Medicine and Rehabilitation, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Korea (S.K., S.N.Y., J.S.Y.); Department of Physical Medicine and Rehabilitation, Seoul Veterans Hospital, Seoul, Korea (J.K.); and Department of Physical Medicine and Rehabilitation, Yeouido St Mary s Hospital, College of Medicine, Catholic University of Korea, Seoul, Korea (S.J.W.). Revision requested March 31, Revised manuscript accepted for publication April 13, Address correspondence to Seung Nam Yang, MD, PhD, Department of Physical Medicine and Rehabilitation, Korea University Guro Hospital, Korea University College of Medicine, 80 Guro-gu, Gurodong, Seoul , Korea. snamyang@korea.ac.kr Abbreviations BMI, body mass index; CMAP, compound muscle action potential; SNAP, sensory nerve action potential doi: /ultra Objectives The aim of this study was to compare the ulnar nerve at the wrist by sonographic and electrophysiologic studies between patients with carpal tunnel syndrome and control participants and to verify the effect of carpal tunnel syndrome of the ulnar nerve at the wrist. Methods Forty-two hands of patients with carpal tunnel syndrome and 37 hands of control participants were examined. Electrophysiologic studies of the ulnar nerve were done in all participants. The cross-sectional areas of the median and ulnar nerves at the wrist were evaluated by sonography. Fifteen hands of patients with carpal tunnel syndrome who underwent carpal tunnel release were also evaluated by sonography after the operation. Results The ulnar nerve cross-sectional area of the patients with carpal tunnel syndrome (mean ± SD, 5.16 ± 1.04 mm 2 ) was significantly larger than that of the controls (3.56 ± 0.52 mm 2 ; P <.0001). After release of the transverse carpal ligament, the crosssectional area of the ulnar nerve was significantly smaller than the size measured prior to surgery (P <.0001). The cross-sectional area of the median nerve was significantly correlated with that of the ulnar nerve (P <.05). However, no statistically significant difference was found between the patients with carpal tunnel syndrome and controls in ulnar nerve conduction. There were no statistically significant differences in nerve conduction study results or cross-sectional area of the ulnar nerve between patients with carpal tunnel syndrome with and without extramedian symptoms. Conclusions The cross-sectional areas of the ulnar and median nerves at the wrist are increased in patients with carpal tunnel syndrome. Also, the cross-sectional area of the ulnar nerve is decreased after carpal tunnel release. Key Words carpal tunnel syndrome; Guyon canal; neurosonology; sonography; ulnar nerve Carpal tunnel syndrome is the most common compression neuropathy of the upper extremity. The main symptoms of carpal tunnel syndrome include paresthesia and pain in the distribution of the median nerve at the fingers and hands. However, the symptoms frequently involve the fingers and portions of the hand innervated by the ulnar nerve as well. The carpal tunnel is located close to the Guyon canal, and increased pressure in the carpal tunnel might affect the ulnar nerve in the Guyon canal at the wrist. The Guyon canal on the medial aspect of the wrist houses the ulnar nerve and artery. 1,2 The roof of the canal includes the volar 2016 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2016; 35:

2 carpal ligament and palmaris brevis, whereas the floor is composed of the transverse carpal ligament, which is the tough fibrous roof of the carpal tunnel, the pisohamate and pisometa carpal ligaments, and the opponens digiti minimi (Figure 1). 2 Several studies evaluated ulnar nerve involvement in carpal tunnel syndrome by using nerve conduction studies. 3,4 One study reported prolonged latencies and decreased amplitudes of ulnar motor and sensory nerve potentials in patients with carpal tunnel syndrome in comparison to a control group. 4 Another study showed decreased ulnar sensory nerve action potential (SNAP) amplitude and velocity in patients with severe carpal tunnel syndrome compared to control participants. 3 Furthermore, the severity of the ulnar nerve conduction abnormality is associated with that of the median nerve. High-resolution sonography has been described as a useful tool for evaluation of the peripheral nerve by measuring its cross-sectional area (CSA). 5 We hypothesized that ulnar nerve involvement in carpal tunnel syndrome can be detected by sonography. The aim of this study was to compare the ulnar nerve cross-sectional area between patients with carpal tunnel syndrome and control participants by electrophysiologic and sonographic studies and to verify the effect of carpal tunnel syndrome on the ulnar nerve at the wrist. We also compared the cross-sectional area of the ulnar nerve before and after carpal tunnel release in patients with carpal tunnel syndrome. Figure 1. Schematic of the median nerve in the carpal tunnel and ulnar nerve in the Guyon canal. The ulnar nerve is located between the transverse carpal ligament and volar carpal ligament, forming the Guyon canal. A indicates ulnar artery; M, median nerve; U, ulnar nerve; arrowheads, volar carpal ligament; and arrows, transverse carpal ligament. Materials and Methods From June 2012 to May 2014, 42 hands of 23 consecutive patients with a clinical and electrophysiologic diagnosis of carpal tunnel syndrome and 37 hands of 19 consecutive healthy volunteers as a control group were enrolled in this study through the Department of Physical Medicine and Rehabilitation at Korea University Guro Hospital. Carpal tunnel syndrome was diagnosed by clinical symptoms (hand pain, numbness, tingling, and weakness) and electrodiagnostic findings. Among these patients, 15 hands of 7 patients with carpal tunnel syndrome who underwent carpal tunnel release were examined with sonography postoperatively. Patients had no history or clinical signs of systemic disease, upper extremity surgery, direct trauma to the upper extremities, entrapment neuropathy other than carpal tunnel syndrome, or generalized peripheral neuropathy. Patients with a diagnosis of ulnar neuropathy at the elbow by electrodiagnosis were eliminated from the study. The control group had no history of peripheral neuropathy or symptoms of numbness, pain, or weakness in any extremity. They underwent electrodiagnostic testing and were excluded if the median nerve conduction was not within the normal limits. This study was approved by the Korea University Guro Hospital Institutional Review Board and written informed consent was obtained from all participants. Extramedian symptoms were defined as symptoms affecting the fifth fingers. Electrodiagnostic Examinations The examinations were performed by a board-certified physiatrist with 10 years of electrodiagnostic experience who was blinded to patient histories. Motor and sensory nerve conduction studies of the median and ulnar nerves were performed in patients with carpal tunnel syndrome and in controls by using the Viking Select system (Nicolet Biomedical, Madison, WI). The motor responses were recorded over the abductor pollicis brevis muscle with median nerve stimulation at the wrist and cubital fossa and over the abductor digiti minimi muscle with ulnar nerve stimulation at the wrist, 3 cm below and 7 cm above the elbow. The sensory responses were obtained by an anti - dromic technique from the third digit with median nerve stimulation at the wrist and palm and from the fifth digit with ulnar nerve stimulation at the wrist. Electrodiagnosis of carpal tunnel syndrome was based on the criteria developed by the American Association of Neuromuscular and Electrodiagnostic Medicine. 6 We classified the severity of electrophysiologic findings for the patients with carpal tunnel syndrome by using the scale of 38 J Ultrasound Med 2016; 35:37 42

3 Padua et al 7 : stage 1,: normal; stage 2, minimal (abnormal distoproximal ratio or other segmental/comparative test results and normal standard test results); stage 3, mild (abnormal sensory nerve conduction velocity and normal distal motor latency); stage 4, moderate (abnormal sensory nerve conduction velocity and abnormal distal motor latency); stage 5, severe (absence of sensory response and abnormal distal motor latency); and stage 6, extreme (absence of median motor and sensory responses). Patients were excluded if they met the diagnostic criteria of ulnar neuropathy at the elbow proposed by the American Association of Neuromuscular and Electrodiagnostic Medicine. 8 The hand temperature in patients and controls was maintained at 32 C or warmer. Sonographic Examinations Sonography was performed with an HD15 system (Philips Healthcare, Bothell, WA) equipped with a 7 12-MHz linear array transducer by another physiatrist, who was blinded to the patients histories and nerve conduction study results. The examiner had been trained in neuromuscular sonography and had more than 10 years of experience. Each participant was placed in the supine position with the elbow and wrist fully extended. The transducer was used to obtain a transverse view of the median and ulnar nerves at the distal wrist crease. The cross-sectional areas of the median and ulnar nerves were calculated by a direct method using a continuous boundary trace just within the hyperechoic rim of the nerve (Figure 2). An effort was made to minimize additional pressure from the probe on the nerve, and care was taken to ensure that the transducer was perpendicular to the nerve. The patients who underwent transverse carpal ligament release surgery were evaluated by sonography of the median and ulnar nerves 3 months postoperatively. Figure 2. Sonogram of the median and ulnar nerves at the wrist. Notations are as in Figure 1. Statistical Analyses All statistical analyses were performed with SAS version 9.2 software (SAS Institute Inc, Cary, NC). Group differences in age, sex, and body mass index (BMI) were evaluated by a ttest and χ 2 test. Variables were tested for normality by the Shapiro-Wilk test. Logarithmic transformations were applied as needed to ensure normal distributions of variables, and a generalized linear model was used. Median and ulnar nerve compound muscle action potential (CMAP) and SNAP latencies and amplitudes and cross-sectional areas were compared between patients with carpal tunnel syndrome and controls after adjustment for age, sex, BMI, and hand side. The correlation between electrophysiologic findings and cross-sectional areas of the median and ulnar nerves was evaluated in patients with carpal tunnel syndrome. Median and ulnar nerves cross-sectional areas were also compared before and after carpal tunnel release surgery in those who underwent the procedure. Results General Characteristics There were no statistically significant differences in terms of age, sex, or BMI between the patient and control groups (Table 1). Twenty-one of 42 hands with carpal tunnel syndrome had paresthesia and pain in the fifth finger as well as the area innervated by the median nerve. According to the Padua scale, electrophysiologic findings of most hands were classified as stage 4, followed by stage 5 and stages 3 and 6 (Table 1). Electrophysiologic and Sonographic Findings On nerve conduction studies, there was no statistically significant difference in the latency or amplitude of the ulnar nerve between the patients with carpal tunnel syndrome and controls. On sonography, the ulnar nerve crosssectional area in the patients with carpal tunnel syndrome was significantly larger than that in the control group. The cross-sectional area of the median nerve in the carpal tunnel syndrome group was significantly larger than that in the control group (Table 2). The cross-sectional area of the ulnar nerve was significantly correlated with the median nerve cross-sectional area, CMAP latency, and SNAP latency, and amplitude. Ulnar nerve conduction study results were significantly correlated with median nerve results (Table 3). There was no correlation between Padua severity and ulnar nerve conduction study results or crosssectional area. There were no statistically significant differences in ulnar nerve conduction study results or cross-sectional area between patients with carpal tunnel J Ultrasound Med 2016; 35:

4 Table 1. General Characteristics of Patients With Carpal Tunnel Syndrome and Control Participants Characteristic Patients Controls Age, y ± ± Male/female 3/20 4/15 Right/left 21/21 18/19 BMI, kg/m ± ± 2.88 Carpal tunnel syndrome duration, wk ± Padua scale Stage 3 3 Stage 4 29 Stage 5 7 Stage 6 3 Data are presented as mean ± SD where applicable. Table 2. Parameters for the Median and Ulnar Nerves at the Wrist in Patients With Carpal Tunnel Syndrome and Control Participants Parameter Patients Controls P Median nerve CMAP latency, ms 5.53 ± ± 0.40 <.0001 CMAP amplitude, mv 6.73 ± ± SNAP latency, ms 4.44 ± ± SNAP amplitude, μv ± ± 6.11 <.0001 Cross-sectional area, mm ± ± 1.18 <.0001 Ulnar nerve CMAP latency, ms 3.04 ± ± CMAP amplitude, mv 9.17 ± ± SNAP latency, ms 3.15 ± ± SNAP amplitude, μv ± ± Cross-sectional area, mm ± ± 0.52 <.0001 Data are presented as mean ± SD. P values represent overall differences across the group based on a generalized linear model. with and without extramedian symptoms (Table 4). Among the 15 hands of the 7 patients who underwent transverse carpal ligament release, the postoperative ulnar crosssectional area was significantly smaller than the preoperative area (Table 5). Discussion Table 3. Correlations of Electrophysiologic and Sonographic Findings Between Median and Ulnar Nerves in Carpal Tunnel Syndrome In our study, the ulnar nerve in patients with carpal tunnel syndrome had a large cross-sectional area on sonography compared to controls. In addition, the ulnar nerve crosssectional area was correlated with the median nerve cross-sectional area in patients with carpal tunnel syndrome, and the ulnar nerve cross-sectional area was decreased after carpal tunnel release. These results suggest that carpal tunnel syndrome results in enlargement of the ulnar nerve in the Guyon canal. Extramedian symptoms are evident in many cases of carpal tunnel syndrome. The exact mechanism is still unknown, but there are several hypotheses. One is reorganization of somatosensory cortex representation after deafferentation of the peripheral nervous system. 9 A previous study found that the cortical somatosensory evoked potential amplitude of the ulnar nerve ipsilateral to carpal tunnel syndrome was increased compared to controls. 10 Tecchio et al 11 found that carpal tunnel syndrome modified sensory hand cortical somatotopy by using a magnetoencephalographic technique. In patients with carpal tunnel syndrome who had paresthesia of the whole hand, enlargement of hand representation in the sensory cortex was observed on magnetoencephalography. Another hypothesis is that high pres- Median Nerve Ulnar Nerve Cross- Cross- CMAP CMAP SNAP SNAP sectional CMAP CMAP SNAP SNAP sectional Latency Amplitude Latency Amplitude Area Latency Amplitude Latency Amplitude Area Median nerve CMAP latency CMAP amplitude a SNAP latency a a SNAP amplitude a a a Cross-sectional area a a a a Ulnar nerve CMAP latency a a a CMAP amplitude a a a a SNAP latency a a SNAP amplitude a a a Cross-sectional area.546 a a a a a Values were estimated by a generalized linear model. a P < J Ultrasound Med 2016; 35:37 42

5 sure in the carpal tunnel may affect the compressive forces on the ulnar nerve in the Guyon canal. In a previous study, the decrease in pressure in the Guyon canal was verified by direct pressure measurement with an angiocatheter attached to a pressure monitor after carpal tunnel release. 12 In our study, the ulnar nerve cross-sectional area was significantly decreased after carpal tunnel release. Follow-up studies with sonography were performed 3 months after carpal tunnel release. Several studies suggested that symptoms and electrophysiologic findings of carpal tunnel syndrome were improved up to 3 months postoperatively and were not significantly changed after then. 13,14 This decrease is thought to be due to the fact that carpal tunnel release decreases the pressure in the Guyon canal, and our findings support the hypothesis that high pressure in the carpal tunnel may affect the compressive force on the ulnar nerve in the Guyon canal. In a study of symptoms in 100 patients with carpal tunnel syndrome confirmed by electromyography, 56.6% had paresthesia of the fifth finger. 15 In our study, 21 of 42 hands with carpal tunnel syndrome had extramedian symptoms, including fifth finger paresthesia and pain, which was consistent with previous work. However, there were no significant differences in ulnar nerve conduction study results and cross-sectional area with regard to extramedian symptoms. Extramedian symptoms are present in various degrees and difficult to quantify, and the presence of extramedian symptoms may not have a substantial effect on ulnar nerve conduction study results and cross-sectional area. In patients with carpal tunnel syndrome, ulnar nerve CMAP latency was delayed, and CMAP and SNAP amplitudes were smaller than in controls, but the differences were not statistically significant. These findings are inconsistent with previous studies. However, ulnar nerve conduction study results were correlated with median nerve results, suggesting that the severity of carpal tunnel syndrome results in a substantial change in ulnar nerve conduction compared to controls. High-resolution sonography is an emerging technique for evaluation of peripheral nerves. 5 Nerve parameters such as diameter and variation in shape have been studied. 16 However, the nerve cross-sectional area is most widely studied and accepted as a consistent parameter for evaluation of nerve disorders. Several studies of normal ulnar nerve cross-sectional area values on sonography have been reported In one study from the United States, the mean cross-sectional area ± SD of the normal ulnar nerve in the wrist crease was determined to be 5.9 ± 1.1 mm In another study of Asian participants, the cross-sectional area of the ulnar nerve at the wrist was 3.6 ± 5.0 mm In these studies, sex, age, weight, BMI, and wrist circumference all significantly affected the ulnar nerve cross-sectional area. In our study, the mean cross-sectional area of the ulnar nerve in the healthy volunteers was 3.56 ± 0.52 mm 2, which was similar to the value reported in the previous study. If the cross-sectional area of the ulnar nerve is increased beyond the normal value on sonography, carpal tunnel syndrome should be considered, as it is one of the causes of ulnar nerve enlargement. This study had several limitations. First, the sample size was small, particularly in the analysis based on postoperative follow-up. In addition, the lack of postoperative electrodiagnostic data would be a potential limitation. Because the sonographic examination showed significant postoperative changes in the cross-sectional areas of the median and ulnar nerves, if more participants could have been enrolled and electrodiagnosis had been performed postoperatively, a more prominent outcome analysis might have been possible. Second, we did not use more sensitive sonographic and electrodiagnostic tests for screening mild carpal tunnel syndrome. For sonographic evaluation of carpal tunnel syndrome, we used the nerve cross-sectional area and did not use another available sensitive screening test. A previous report has suggested that the wrist-to-forearm ratio Table 4. Parameters for the Median and Ulnar Nerves at the Wrist in Patients With Carpal Tunnel Syndrome and Control Participants With Without Parameter Symptoms Symptoms P Median nerve CMAP latency, ms 5.44 ± ± CMAP amplitude, mv 7.01 ± ± SNAP latency, ms 4.74 ± ± SNAP amplitude, μv ± ± Cross-sectional area, mm ± ± Ulnar nerve CMAP latency, ms 2.85 ± ± CMAP amplitude, mv 9.16 ± ± SNAP latency, ms 3.12 ± ± SNAP amplitude, μv ± ± Cross-sectional area, mm ± ± Notations are as in Table 2. Table 5. Differences in Cross-sectional Area After Carpal Tunnel Release Parameter Before Release After Release P Median nerve crosssectional area, mm ± ± 7.00 <.0001 Ulnar nerve crosssectional area, mm ± ± 0.84 <.0001 Notations are as in Table 2. J Ultrasound Med 2016; 35:

6 of the median nerve cross-sectional area is a more sensitive parameter compared to the cross-sectional area at the wrist. 20 For electrodiagnosis, we used the American Association of Neuromuscular and Electrodiagnostic Medicine criteria for carpal tunnel syndrome diagnosis and the Padua scale for severity classification. Recently, a more effective diagnostic tool using a combined sensory index in mild carpal tunnel syndrome was reported. 21 Thus, some of the control hands may have been misclassified because there is a possibility that they had asymptomatic median neuropathy. This factor could have affected the subsequent electrodiagnostic test results by falsely reducing the differences in both median and ulnar nerve results for the carpal tunnel syndrome group versus the control group. Third, we did not screen participants with ulnar neuropathy at the elbow using sonography. Although we screened the participants with ulnar neuropathy at the elbow using electrodiagnosis, if we have used sonography as an additional screening tool, ulnar nerve lesions at the elbow could have been more precisely evaluated. Finally, about one-third of the carpal tunnel syndrome cases were Padua stage 4, and the severity of carpal tunnel syndrome was not diverse. Further studies with various degrees of carpal tunnel syndrome are required. Although we attempted to measure the ulnar nerve on sonography when the nerve was most widely viewed, the ulnar nerve measurements may have been affected by the ulnar artery because of the close proximity between them. In conclusion, we have demonstrated that not only the cross-sectional area of the median nerve but also that of the ulnar nerve is increased in patients with carpal tunnel syndrome. In addition, the cross-sectional areas of the median and ulnar nerves are decreased after carpal tunnel release. However, a statistically significant difference was not observed in ulnar nerve conduction study results between the patients with carpal tunnel syndrome and controls. These findings indicate that the ulnar nerve as well as the median nerve is affected by carpal tunnel syndrome. References 1. Cardoso R, Szabo RM. Wrist anatomy and surgical approaches. Hand Clin 2010; 26: Ghasemi-Rad M, Nosair E, Vegh A, et al. A handy review of carpal tunnel syndrome: from anatomy to diagnosis and treatment. World J Radiol 2014; 6: Ginanneschi F, Milani P, Mondelli M, Dominici F, Biasella A, Rossi A. Ulnar sensory nerve impairment at the wrist in carpal tunnel syndrome. Muscle Nerve 2008; 37: Yemisci OU, Yalbuzdag SA, Cosar SN, Oztop P, Karatas M. Ulnar nerve conduction abnormalities in carpal tunnel syndrome. Muscle Nerve 2011; 44: Walker FO, Cartwright MS, Wiesler ER, Caress J. Ultrasound of nerve and muscle. Clin Neurophysiol 2004; 115: Jablecki CK, Andary MT, So YT, Wilkins DE, Williams FH. 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