Differences in risk factors for neurophysiologically confirmed carpal tunnel syndrome and illness with similar symptoms but normal median nerve function: a case-control study.

BACKGROUND: To explore whether risk factors for neurophysiologically confirmed carpal tunnel syndrome (CTS) differ from those for sensory symptoms with normal median nerve conduction, and to test the validity and practical utility of a proposed definition for impaired median nerve conduction, we carried out a case-control study of patients referred for investigation of suspected CTS. METHODS: We compared 475 patients with neurophysiological abnormality (NP+ve) according to the definition, 409 patients investigated for CTS but classed as negative on neurophysiological testing (NP-ve), and 799 controls. Exposures to risk factors were ascertained by self-administered questionnaire. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by logistic regression. RESULTS: NP+ve disease was associated with obesity, use of vibratory tools, repetitive movement of the wrist or fingers, poor mental health and workplace psychosocial stressors. NP-ve illness was also related to poor mental health and occupational psychosocial stressors, but differed from NP+ve disease in showing associations also with prolonged use of computer keyboards and tendency to somatise, and no relation to obesity. In direct comparison of NP+ve and NP-ve patients (the latter being taken as the reference category), the most notable differences were for obesity (OR 2.7, 95 % CI 1.9-3.9), somatising tendency (OR 0.6, 95% CI 0.4-0.9), diabetes (OR 1.6, 95% CI 0.9-3.1) and work with vibratory tools (OR 1.4, 95% CI 0.9-2.2). CONCLUSIONS: When viewed in the context of earlier research, our findings suggest that obesity, diabetes, use of hand-held vibratory tools, and repeated forceful movements of the wrist and hand are causes of impaired median nerve function. In addition, sensory symptoms in the hand, whether from identifiable pathology or non-specific in origin, may be rendered more prominent and distressing by hand activity, low mood, tendency to somatise, and psychosocial stressors at work. These differences in associations with risk factors support the validity of our definition of impaired median nerve conduction.

Impact of carpal tunnel surgery according to pre-operative abnormality of sensory conduction in median nerve: a longitudinal study.

BACKGROUND: We have previously proposed that sensory nerve conduction (SNC) in the median nerve should be classed as abnormal when the difference between conduction velocities in the little and index fingers is > 8 m/s. In a prospective longitudinal study, we investigated whether this case definition distinguished patients who were more likely to benefit from surgical treatment. METHODS: We followed up 394 patients (response rate 56%), who were investigated by a neurophysiology service for suspected carpal tunnel syndrome. Information about symptoms, treatment and other possible determinants of outcome was obtained through questionnaires at baseline and after follow-up for a mean of 19.2 months. Analysis focused on 656 hands with numbness, tingling or pain at baseline. Associations of surgical treatment with resolution of symptoms were assessed by Poisson regression, and summarised by prevalence rate ratios (PRRs) and associated 95% confidence intervals (95% CIs). RESULTS: During follow-up, 154 hands (23%) were treated surgically, and sensory symptoms resolved in 241 hands (37%). In hands with abnormal median SNC, surgery was associated with resolution of numbness, tingling and pain (PRR 1.5, 95% CI 1.0-2.2), and of numbness and tingling specifically (PRR 1.8, 95% CI 1.3-2.6). In contrast, no association was apparent for either outcome when median SNC was classed as normal. CONCLUSIONS: Our definition of abnormal median SNC distinguished a subset of patients who appeared to benefit from surgical treatment. This predictive capacity gives further support to its validity as a diagnostic criterion in epidemiological research.

Symptoms, signs and nerve conduction velocities in patients with suspected carpal tunnel syndrome.

BACKGROUND: To inform the clinical management of patients with suspected carpal tunnel syndrome (CTS) and case definition for CTS in epidemiological research, we explored the relation of symptoms and signs to sensory nerve conduction (SNC) measurements. METHODS: Patients aged 20-64 years who were referred to a neurophysiology service for investigation of suspected CTS, completed a symptom questionnaire (including hand diagrams) and physical examination (including Tinel's and Phalen's tests). Differences in SNC velocity between the little and index finger were compared according to the anatomical distribution of symptoms in the hand and findings on physical examination. RESULTS: Analysis was based on 1806 hands in 908 patients (response rate 73%). In hands with numbness or tingling but negative on both Tinel's and Phalen's tests, the mean difference in SNC velocities was no higher than in hands with no numbness or tingling. The largest differences in SNC velocities occurred in hands with extensive numbness or tingling in the median nerve sensory distribution and both Tinel's and Phalen's tests positive (mean 13.8, 95% confidence interval (CI) 12.6-15.0 m/s). Hand pain and thumb weakness were unrelated to SNC velocity. CONCLUSIONS: Our findings suggest that in the absence of other objective evidence of median nerve dysfunction, there is little value in referring patients of working age with suspected CTS for nerve conduction studies if they are negative on both Tinel's and Phalen's tests. Alternative case definitions for CTS in epidemiological research are proposed according to the extent of diagnostic information available and the relative importance of sensitivity and specificity.