Carpal tunnel syndrome severity and manual work: a case-control study

Carpal tunnel syndrome (CTS) is a socially relevant con- dition. This case-control study aims to investigate the asso- ciation between CTS severity and manual work considering personal anthropometric risk factors as well. We prospec- tively and consecutively enrolled one CTS case for two con- trols regardless of age and gender who were admitted to the same three outpatient electromyography labs. CTS diag- nosis was made according to clinical findings and distal conduction delay of the median nerve. Case and controls with diabetes, connective and thyroid diseases, renal failure, polyneuropathy, cervical radiculopathy, wrist trauma were excluded, as well as, women in pregnancy or lactation. CTS cases were grouped in two classes of progressive clinical and electrophysiological severity according to two validated five-stage scales: mild (stages I/II) and moderate/severe (stages III-IV-V). Anthropometric measures and occupational history were collected for both cases and controls. Job titles were coded according to the International Standard Clas- sification of Occupations (ISCO 88) by two occupational physicians who were blind to case/control status. Job titles were grouped in two main occupational categories: manual workers and non-manual workers. To assess the association between CTS severity and manual work, multinomial logis- tic regression models (adjusted for age, sex, wrist-palm ratio and waist-stature ratio) were performed. Relative risk ratios (RRR) and 95% confidence intervals (95% CI) were calcu- lated taking controls as reference category. This case-control study enrolled 370 cases and 747 controls. After the exclu- sion of retired subjects and housewives, we included 224 cases (age 47.6±12.0 yrs; 154 females, 70 males) and 500 controls (age 42.8±11.6 yrs; 299 females, 201 males) in the main analysis. These subjects were grouped in 496 manual workers and 228 non-manual workers. For manual workers in respect to non-manual workers, the RRR for the electrophysiological severity scale were 2.6 (95%CI 1.4–4.7) for the mild class and 3.3 (95%CI 2.0–5.6) for the moder- ate/severe class. Regarding the clinical severity scale, the RRR for manual workers compared to non-manual workers were 3.3 (95% CI, 2.0–5.4) in the mild stage and 2.5 (95% CI, 1.3–4.8) in the moderate/severe stage. This study con- firms that manual work is an important risk factor for CTS, independently of personal anthropometric risk factors. The association between manual work and CTS severity tends to increase from mild to severe stage of electrophysiological scale. This kind of trend does not seem to be confirmed in the case of subjective symptoms as evaluated by the clinical scale.