Total oxidative stress and antioxidant status in patients with carpal tunnel syndrome

Abstract

Objectives

Studies in the carpal tunnel syndrome (CTS) are supported ischemia-induced changes rather than inflammation of the flexor tenosynovium. In this study, total antioxidant status (TAS), total oxidative stress (TOS) and oxidative stress index (OSI) in patients with CTS has been investigated.

Methods

Forty-three patients (38 female and 5 male, 81 hands in total) diagnosed as CTS after the physical examination and electrophysiological findings included in study. The mean age of patients was 43.30 ± 10.49 years.

Results

Bilateral CTS in 38 (88%) patients and unilateral CTS in five patients were detected. Dominant hand was involved in all patients. The mean symptoms duration was 30.9 months (range, 5–67 months). TAS in patients with CTS was significantly lower compared with control (1.01 ± 0.14 versus 1.11 ± 0.20 mmol Trolox equiv./l), (P = 0.008). TOS and OSI in patients with CTS were significant higher compared with control (15.60 ± 7.03 versus 11.86 ± 2.18 µmol H2O2 equiv./l and 1.57 ± 0.72 versus 1.09 ± 0.28), (respectively P = 0.002 and <0.001).

Conclusion

This study shows that there is a change in the oxidative stress and antioxidant defences in patients with CTS. Increased TOS and OSI and decreased TAS might be stimulate fibrosis through disturbed signaling pattern in the tenosynovium and median nerve. These processes might play a role in occurrence and progression of CTS.

Keywords:

• Antioxidant status
• Carpal tunnel syndrome
• Oxidative stress index
• Pathogenesis
• Total oxidative stress

Introduction

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy, with a reported prevalence of 6%. CTS is caused by compression of the median nerve beneath the transverse carpal ligament¹ and is a major cause of pain and disability.² Further, the incidence of CTS is not decreasing.³

The etiology of CTS is most often idiopathic, although it can be related to a variety of medical conditions, including rheumatoid arthritis, hypothyroidism and hyperthyroidism, sarcoidosis, gout, and diabetes mellitus, as well as certain anatomic variants.^2–4

Fibrosis of the subsynovial connective tissue is the most characteristic histopathologic finding in patients with CTS. It is uncertain as to whether changes in the subsynovial connective tissue are primary or secondary.⁴

Histological studies of the flexor tenosynovium also support ischemia-induced changes rather than inflammation. Ischemia-induced reperfusion injury causes cellular damage leading to extravasation of fluid, which is rapidly absorbed by the synovium, producing edema and compression of the nerve.⁵

Reactive oxygen species (ROS) are highly reactive transient chemical species, such as nitric oxide, superoxide, and hydroxyl radical anion. Normal cellular metabolism appears to be a primary source for endogenous ROS. Evasion of endogenous ROS from antioxidant pathways (e.g. glutathione peroxidase, vitamin E) result in the background levels of modification of cellular molecules, which can be detected in normal tissue. However, when the production of damaging ROS exceeds the capacity of the body's antioxidant defenses, a condition known as oxidative stress occurs.⁶ Freeland et al.⁷ found a significant increase in the serum malondialdehyde as biomarker for oxidative stress as well as tenosynovial levels of malondialdehyde compared with controls in the patients with CTS.

Serum total antioxidant status (TAS), total oxidative stress (TOS), and oxidative stress index (OSI) in patients with CTS has not been investigated previously. In this study, we examined serum TAS, TOS, and OSI values in patients with CTS and compared them with healthy controls.

Patients and methods

Subjects complaining of pain and paresthesia in median nerve region of hand who applied to Harran University Research Hospital Physical Medicine and Rehabilitation outpatient clinic were examined. Forty-three patients (38 female and 5 male, totally 81 hands) diagnosed as CTS after the history, physical examination and electrophysiological findings included in the study. Informed consent was obtained from each CTS patient.

Forty-three age-matched and body mass index (BMI)-matched healthy controls were enrolled in the study. Controls had no joint complaints and any rheumatological disease. None of the controls smoked or consumed alcohol. Informed consent was obtained from each control. Patients who had systemic, metabolic, malign diseases, fibromyalgia syndrome, cervical disc disease, infection, or spinal surgery as well as patients with laboratory abnormalities were excluded from the study.

Range of motion, muscle strengths, hypoesthesia (light touch and pinprick), fingertip 2-point discrimination, and specific tests for CTS (Tinel test, Phalen maneuver, reverse Phalen maneuver) were carried out. CTS patient global pain score (visual analog scale, VAS 0–10 mm) was measured and Boston Carpal Tunnel Questionnaire (BQ) was applied.⁸ The BQ consists of two components: symptom severity scale (SSS) with 11 items and functional status scale (FSS) with 8 items. A Turkish version of BQ validated by Sezgin et al.⁹ was used. The BQ was presented in multiple-choice format, and scores were assigned from 1 point (mildest) to 5 points (most severe). Each score was calculated as the mean of the responses of the individual items.¹⁰

Electrophysiologic testing

All tests were done in the same room and in room temperature conditions using Nihon Kohden 4 ME 8 electrode entrance 4 record channel device (Neuropack MEB-2300, Japan’). Skin temperature on the hand was measured and maintained between 32.0 and 34.0°C. All participants underwent median and ulnar nerve sensorimotor nerve conduction study. The median and ulnar nerves were stimulated at the wrist and elbow (antecubital region for median nerve, ulnar fossa for ulnar nerve) at a distance of 8 cm from the wrist to the active electrode. Sensory responses were obtained antidromically. Ring electrodes were used to obtain sensory nerve action potentials. Electrodes were placed over the second finger for the median nerve and fifth finger for the ulnar nerve. The active recording electrode was placed more proximally, closest to the stimulator. The median and ulnar nerves were stimulated at the wrist and elbow (antecubital region for median nerve, ulnar fossa for ulnar nerve).¹¹

Blood sampling

After an overnight fasting, venous blood was withdrawn into heparinized tubes. Remaining blood was centrifuged at 1000 × g for 10 minutes to separate the plasma and the serum samples were stored at −80°C until analysis.

Measurement of total antioxidant status

Serum TAS levels were determined using a novel automated measurement method, developed by Erel.¹² In this method, hydroxyl radical, which is the most potent radical, is produced via Fenton Reaction. Antioxidative effect of the sample against the potent-free radical reactions, which is initiated by the produced hydroxyl radical, is measured. The assay has got excellent precision values, which are lower than 3%. The results are expressed as mmol Trolox equiv./l. Analytical sensitivity was reported to be 0.11 absorbance/amount [AX (mM)⁻¹].

Measurement of total oxidant status

Serum TOS levels were determined using a novel automated measurement method, developed by Erel.¹³ In this method, oxidants present in the sample oxidize the ferrous ion-o-dianisidine complex to ferric ion. The assay is calibrated with hydrogen peroxide and the results are expressed in terms of micromolar hydrogen peroxide equivalent per liter (μmol H₂O₂ equiv./l). Analytical sensitivity was reported to be 0.0076 absorbance/amount, [AX (μM)⁻¹].

Oxidative stress index

The percent ratio of the TOS to the TAS gave the OSI, an indicator of the degree of oxidative stress.^12,13 OSI (arbitrary unit) = TOS (μmol H₂O₂ Eq/l)/TAC (mmol Trolox Eq/l).

Statistical method

Statistical analysis was performed with SPSS 16.0 (SPSS for Windows 16.0, Chicago, IL, USA). All parameters were analyzed with One-sample Kolmogorov–Smirnov test for normal distribution. Arithmetic mean values and standard deviations (SDs) of the data were detected. We performed t tests to compare the patient and the healthy controls. The Spearman rank test was applied to calculate the correlation coefficients of SSS and FSS with the electrophysiologic parameters. Next, stepwise multiple regression analyses concerning SSS and FSS as the predicted variables were performed. A P value of <0.05 was considered to be significant. Data are presented as mean ± SD.

Results

This study included 38 female (88%) and 5 male (12%) patients. Healthy subjects comprised 36 female and 7 male. The mean age of the patient group was 43.3 ± 10.5 (23–65) years and control group was 41.8 ± 9.9 (23–65) years (P > 0.05). BMI values in CTS patients and controls were 29 ± 4.1 and 27.9 ± 3.5 kg/m², respectively. There was no difference between CTS patients and controls in age, gender, and BMI. Demographic features of patients were shown Table 1.

Table 1. Demographic characteristics

	Subjects with CTS (n:43)	Controls (n:43)	P value
Age (years)	43.30 ± 10.48 (23–65)	41.76 ± 9.92 (23–65)	>0.05
Gender	38 Female (88%), 5 male (12%)	36 Female (84%), 7 male (16%)	>0.05
Body mass index (kg/m^2)	29.10 ± 4.08 (20.06–37.46)	27.92 ± 3.46 (20.76–36.44)	>0.05

The age and BMI values represent the mean ± SD.

Bilateral CTS in 38 (88%) patients and unilateral CTS in 5 patients were detected. Dominant hand was involved in all patients. The mean duration of symptoms was 30.9 months (range, 5–67 months).

We found a positive correlation between SSS and FSS of BQ and VAS (r = 0.51 and 0.35, respectively, P < 0.001). There was a negative correlation between SSS of BQ and dominant hand nerve conduction velocity (P = 0.033). Between SSS and dominant hand distal motor latency found a positive correlation (P = 0.012). As nerve conduction velocity decreased and distal motor latency prolonged in dominant hand was diminished the FSS of BQ in our patients (P < 0.001) (Table 2).

Table 2. Clinical and electromyographic findings in patients with CTS

	Patient (n:43, total 81 hands)
Symptom duration (months)	30.9 (5–67)
VAS (mm)	7.02 ± 1.16 (5–9)
Boston Questionnaire	41.81 ± 7.53 (29–60)
SSS	24.83 ± 4.85 (16–36)
FSS	17.20 ± 3.29 (9–26)
Right NCV	35.42 ± 11.03 (0–45.80)
Right motor latency	4.92 ± 1.49 (3.15–9.55)
Left NCV	36.74 ± 13.47 (0–57.00)
Left motor latency	4.63 ± 1.46 (3.15–10.35)

NCV, nerve conduction velocity.

The values except for symptom duration represent the mean ± SD.

TAS in patients with CTS was significantly lower compared with healthy subjects (1.01 ± 0.14 versus 1.11 ± 0.20, P = 0.008) (95% confidence interval, −0.1763 to −0.0271), TOS and OSI in patients with CTS were significantly higher compared with control (respectively P = 0.002 and <0.001) (Table 3).

Table 3. Serum total antioxidant status, total oxidative stress, and oxidative stress index values in patients with carpal tunnel syndrome

	Subjects with CTS (n:43) mean ± SD	Controls (n:43) mean ± SD	P value
TAS (mmol Trolox Eq/l)	1.01 ± 0.14 (0.62–1.33)	1.11 ± 0.20 (0.83–1.77)	0.008
TOS (μmol H2O2 Eq/l)	15.60 ± 7.03 (8.50–37.13)	11.86 ± 2.18 (8.36–17.20)	0.002
OSI (arbitrary unit)	1.57 ± 0.72 (0.84–3.67)	1.09 ± 0.28 (0.47–1.83)	<0.001

The values represent the mean ± SD.

No statistically significantly correlations were detected between age, BMI, and disease duration and TAS, TOS, OSI values in CTS patients (P > 0.05).

Discussion

This study is the first study in the literature on TAS, TOS, and OSI values in patients with CTS. Our results suggest that an imbalance between the oxidant and antioxidant systems defined as oxidative stress have main role in the pathogenesis of CTS.

Both mechanical and ischemic factors have been implicated in the causation of symptoms of median nerve compression. However, the actual mechanism of pathogenesis is not completely understood. Observations of biochemical and histological changes occurring locally and systemically during this process give some insight into the mechanism. Repetitive motion as well as alteration in wrist position lead to an intermittent rise in interstitial pressure and interrupted chronic compression of the median nerve in predisposed patients. Intermittent perfusion of the cellular tissue, once ischemia is relieved, prior to surgery produces free oxygen radicals. Alternating compression and reperfusion may occur, particularly in repetitive function cumulative trauma disorders. With continued oxidative stress, the human body's normal antioxidant defense system becomes overwhelmed, and cellular injury ensues. Tissue injury and its response were seen in the flexor tenosynovium as well as median nerve.⁵ A classic antioxidant is an agent that can rapidly react with ROS, producing less-reactive species. Antioxidants decrease oxidative stress and restore redox balance in biologic systems.¹⁴

Studies proposed that oxidative stress was closely related to the pathogenesis of several inflammatory diseases such as rheumatoid arthritis, Behcet disease and ankylosing spondylitis,^6,15–17 and lung fibrosis.¹⁶ However, TAS, TOS, and OSI values in patients with CTS have not been reported previously.

It has been detected increased serum malondialdehyde, an indicator of cell stress, in patients with CTS, but no serum increases in PGE2, interleukin (IL)-1, or IL-6.¹⁸ Bioactive substances such as cytokines and prostaglandins might induce swelling of the flexor tenosynovium in the absence of inflammatory cell infiltration.^3,19

We found that an inverse relationship between pain severity and symptom duration. These data support the concept that, in the majority of patients with CTS, the symptoms relate to problems with the connective tissue surrounding the nerve rather than to pathology of the nerve fibers themselves.¹⁹ Although patients in the late phase show severe motor and sensory disturbances, they often complain of less pain than in the early phase. Thus, it would appear that CTS symptoms correlate more with early tenosynovial changes than with later changes.^19–21

Atherosclerosis and related diseases have emerged as the leading cause of morbidity and mortality in the western world. Free radicals and ROS have been suggested to be part of the pathophysiology of these diseases.²² Oxidative stress is therefore a critical feature in atherogenesis. ROS are responsible for direct damage to cellular structures within the vascular wall.²³ Increased lipid peroxidation in terms of increased malondialdehyde (MDA) levels includes low-density lipoprotein (LDL) oxidation and it is possible to conclude that decreased antioxidant capacity plays an important role in the development and progression of atherosclerosis.^24,25

Shiri et al.²⁶ also suggested that CTS may be a manifestation of atherosclerosis, or that both conditions may have common risk factors.²⁶ These common risk factors possibly affect on imbalance between oxidant and antioxidant systems. Therefore, serum oxidant levels might be attributing directly or indirectly to tenosynovial changes and CTS.

However, our results should be interpreted cautiously, as the sample size was relatively small. Ranges for TAS and TOS assays in the normal controls are quite wide and overlapped the values found in our 43 CTS patients. Therefore, it may be also a subset of individuals in the normal population who have a biochemical profile which might predispose to CTS.

In conclusion, we found that the serum TOS and OSI values were higher and TAS levels were lower in patients with CTS than those of healthy controls. Therefore, increased serum TOS and OSI values and decreased serum TAS levels would be stimulating fibrosis patients with CTS through disturbed signaling pattern in the tenosynovium and median nerve. Further investigations on the role of oxidative stress in the etiopathogenesis of CTS might enlighten the development of novel therapeutic approaches for CTS.