Study to Improve Diagnostic Methods for Repetitive Strain Injuries such as Carpal Tunnel Syndrome
| Principal investigator(s): | Ron House
(St. Michael's Hospital) |
| Co-investigator(s): | Michael Wills
(St. Michael's Hospital) |
| Sponsoring Institution: | St. Michael's Hospital |
Objective
The objective of the study was to determine if nerve conduction study (NCS) normal values differ between manual and non-manual workers, and, if so, whether this is an effect of anthropomorphic factors and/or subclinical pathology.
Method
Participants were initially screened by a standard questionnaire to select only those free of neurological symptoms in the upper extremities. A total of 41 manual workers and 41 non-manual workers were selected with matching for age in 10 year age intervals. Motor and sensory NCS of the upper extremities were carried out in all participants and evaluated in terms of differences related to manual vs non-manual work, various anthropomorphic measures and other factors.
Results
Some sensory NCS results differed significantly between manual and non-manual workers. This difference was explained by two factors. First, manual workers had, on average, larger hands and larger finger circumference than non-manual workers and larger finger circumference was associated with a reduction in measured sensory amplitude. In fact finger circumference was the best predictor of sensory amplitudes recorded from the hand and fingers, overshadowing the effect of any other anthropomorphic variable or age. Second, a higher incidence of subclinical median neuropathy at the wrist was found in manual workers and likely accounted for most or all of the remaining difference between manual and non-manual workers
Conclusions
It is important to recognize the effect of hand size on the measurement of nerve function when diagnosing occupational neurological abnormalities. In particular the large, thickened hands of manual workers are associated with decreased measured sensory amplitudes that can affect the interpretation of nerve conduction studies. Specifically, it can result in false positive diagnoses of neuropathy such as carpal tunnel syndrome in manual workers. Recognition of this measurement issue should result in improved interpretation of the effect of hand size on the measurement of nerve function in manual workers and improved diagnostic accuracy. In particular, there should be a reduction in false positive diagnoses of neuropathy such as carpal tunnel syndrome and a consequent decrease in unnecessary interventions such as surgery with secondary loss of grip strength and reduction in work capability. Subclinical median neuropathy at the wrist is very common in manual workers and correlation between symptoms and nerve conduction study results is essential for accurate clinical diagnosis.
For more information:
houser@smh.toronto.on.ca
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