Factors Showing Conflicting Risk of CTS
Limited evidence supports that the following factors have conflicting results regarding the development of carpal tunnel syndrome (CTS):
• Diabetes
• Age
• Gender/Sex
• Genetics
• Comorbid drug use
• Smoking
• Wrist bending
• Workplace

Rationale
Diabetes showed a conflicting relationship to CTS development.  One high quality study (Armstrong, 2008) did not demonstrate a significant association with CTS. The odds ratio was elevated but there was a wide confidence interval that included a value of 1.0 (OR 2.45, CI: 0.92-6.53).  Three moderate quality studies (Becker, 2002; Geoghegan, 2004; Plastino, 2011) found significant associations between diabetes and an increased risk of CTS and one (Coggon, 2013) did not find an association.
 
Age showed a conflicting relationship to CTS development. Two high quality studies (Armstrong, 2008; Bonfiglioli, 2013) showed increased risk in older workers on a continuous scale. Two other high quality studies (Evanoff, 2014; Garg, 2012) measuring age on a continuous scale showed insignificant results but with slightly increased risk ratios and narrow confidence limits. Two moderate quality studies (Morgenstern, 1991; Shin, 2008) also found a significantly increased risk of CTS when measuring age continuously and one moderate quality study (Silverstein, 1987) found an insignificant relationship. When measured categorically, one high quality study (Hakim, 2002) showed an increasing association at age >46 and one moderate quality study (Violante, 2007) found an increasing association among all categories.  Two moderate quality studies (Eleftheriou, 2012; Mondelli, 2006) did not find a significant association between categories of age and CTS development.
 
Female gender/sex was associated with increased risk of CTS in one high quality (Bonfiglioli, 2013) and three moderate quality studies (Burt, 2011; Eleftheriou, 2012; Violante, 2007), while two high quality (Armstrong, 2008; Evanoff, 2014) and two moderate quality studies (Shin, 2008; Silverstein, 1987) showed no significant association.
 
Family history/genetics was associated with increased risk of CTS in one high quality (Hakim, 2002) and two moderate quality studies (Bonfiglioli, 2007; Burt 2011), while two moderate quality studies (Nordstrom, 1997; Violante, 2007) showed no significant correlation. The studies used varying diagnostic methods, and two of the studies evaluated female populations, which may have contributed to the conflicting results.
 
Comorbid drug use showed a conflicting relationship to CTS development. One high quality study (Hakim, 2002) found no association with thyroxine replacement. One moderate quality study (Geoghegan, 2004) reported an increasing risk of CTS with insulin, sulphonyl, or thyroxine.  Two moderate quality studies reported no association to CTS when using diuretics (Morgenstern, 1991) or metformin (Geoghegan, 2004).
 
Smoking had a conflicting relationship to CTS development. Two moderate quality studies (Eleftheriou, 2012; Violante, 2007) found an association of increasing risk, one moderate quality study (Coggon, 2013) found an inverse association, and one moderate quality study (Geoghegan, 2004) found no association.
 
Wrist bending had a conflicting relationship to CTS development. One high (Armstrong, 2008) and one moderate quality study (De Krom, 1990) showed an increased risk while two moderate quality studies (Dale, 2014; Evanoff, 2012) displayed an insignificant association. One moderate quality study (Nordstrom, 1997) showed an insignificant result with a short duration of wrist bending and an increased risk of CTS with more frequent wrist bending.
 
Many recent high and moderate quality studies were identified and provide new insights into workplace factors associated with CTS.  However, the studies did not consider the relative contributions of personal and work-related factors on CTS, so it is difficult to calculate risk attributable to different risk factors from the data. Some occupational factors and workplace exposures were evaluated by single studies with weak designs or relatively weak exposure assessment methods.  The findings from those studies, therefore, did not contribute to the conclusions. Workplace categories include: clerical/office work, industrial, construction, farming, hospital, professional, technical, managerial, sales, skilled trades (agriculture, fabrication, machining, transporter techs, electricians, plumbers, construction), and other jobs. 

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