Carpal Tunnel Syndrome:
Occupationally related or not?

Craig Uejo, M.D., M.P.H.,
AMA Guides Newsletter, May/June 2009

Carpal tunnel syndrome is the most common peripheral entrapment neuropathy and despite ergonomic workplace modifications, rates of so-called work-related musculoskeletal disorders, such as CTS, have not decreased over the past 10 years.  This suggests the presumed occupational risk factors are not the major cause of CTS, but instead other non-work factors are claiming a more significant etiological role than previously thought. However, by either legislation or convention, CTS is often regarded as industrially related. 

Computer use has been reported as the common reason for developing the condition. However, more recent reports have not supported a causal relationship between CTS and typing on a computer keyboard, a repetitive but low-force activity.  The prevalence of CTS in the overall population has been variably reported as 0.7% to 9% for women and 0.4% to 2% for men.  The author referred to a study by Stevens, et. al, who found a prevalence of electrodiagnostically confirmed CTS in 3.5% of frequent computer users.  However, the affected and unaffected employees had similar occupations, years using a computer, and time using a computer during the day.  They noted the frequency of carpal tunnel syndrome in computer users was similar to that in the general population.  Computer use does not pose a severe occupational hazard for developing carpal tunnel syndrome. 

They referred to an additional study determining the prevalence of CTS among intensive keyboard users in a data entry company at 1.1%, lower than expected in the general population.  They referred to more recent research confirming that those who perform intensive keyboard use in the workplace have a lower risk of CTS than those who do not.  Keyboard use may be protective since repeated low-force muscle activity and tendon motion may decrease swelling and tissue pressure. 

The author cites more recent articles suggesting other risk factors, such as age, obesity, hand dominance, reduced physical fitness, lifetime alcohol intake and smoking as primary causes of CTS.  Larger population studies found that weight and body mass correlated strongly with prolonged median nerve latency.  The author referred to additional studies documenting the relationship of the female gender, obesity, a high BMI, age over 30, repetitive motion activities and a number of systemic diseases, such as diabetes, rheumatoid arthritis, and hypothyroidism. 

A genetic predisposition to CTS in women has also been shown in a recent study involving twins and that monozygotic twins had a higher risk of developing CTS than dizygotic twins after adjustment for environmental risk factors.  These studies noted that 50% of liability of CTS in women is genetically determined with the remaining half from other risk factors.  Other risk factors that have been discussed in the literature include oral contraceptives, renal and thyroid disease, rheumatological disorders, including gout and rheumatoid arthritis and pregnancy. 

Trauma as a rare cause of CTS and condition is almost always an illness rather than an injury.  Factors of distal radius and carpal bones or wrist dislocation may result in acute median nerve compression due to bony displacement and/or associated edema. 

With respect to work relationship and CTS, the author refers to literature supporting a causal connection in a relatively small number of jobs, primarily those involving high force and repetition.  Exposure to cold and prolonged vibration are also risk factors. 

The author concludes that the etiology of carpal tunnel syndrome is usually multi-factorial and that significant risk factors include genetics, age, female gender, and obesity. Although in the past, CTS was often considered an occupational illness, the recent medical literature suggests most cases previously labeled as occupation-related were neither caused nor aggravated by work.  

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