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Carpal tunnel syndrome diagnosis in occupational epidemiological studies
  1. F S Violante1,
  2. R Bonfiglioli1,
  3. M Hagberg2,
  4. D Rempel3
  1. 1Department of Medical and Surgical Science, Occupational Medicine, Alma Mater Studiorum University of Bologna, Bologna, Italy
  2. 2Department of Public Health and Community Medicine, Occupational and Environmental Medicine, University of Gothenburg (UGOT), Gothenburg, Sweden
  3. 3Division of Occupational and Environmental Medicine, University of California, San Francisco, USA
  1. Correspondence to Dr Roberta Bonfiglioli, Occupational Health Unit, University of Bologna, Sant'Orsola Malpighi Hospital, via Palagi 9, Bologna 40138, Italy; roberta.bonfiglioli{at}unibo.it

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The problem of the possible over-diagnosis of carpal tunnel syndrome (CTS) has been raised in the Occup Environ Med.13 CTS, like almost all medical conditions, occurs along a spectrum of presentation, progression and severity and, therefore, the alignment between symptoms, signs and objective tests is imperfect. A finding often misunderstood and reported in general population and workplace studies, is the dissociation between CTS symptoms and median nerve conduction slowing at the wrist.47 CTS symptoms and nerve conduction slowing have two different mechanisms, nerve sensory fibres autonomous discharge and conduction block (and or slowing) of the fastest nerve fibres. The two phenomena are likely due to the same causal factor, for example, compression of the median nerve in the carpal tunnel, but the processes are different, so it should not be surprising that in some individuals the onset of these changes do not occur at the same time. Furthermore, there are no internationally accepted standards for abnormal median nerve conduction at the wrist; thresholds between laboratories vary, and this variability and differences in test methods can have an impact on case classification.

In epidemiological studies of CTS, the goal is to describe the distribution of a disease in a selected population, to understand the causal association with risk factors, and to assess the effectiveness of preventive measures. Low specificity case definitions have been used based mainly on symptoms consistent with CTS and possibly a physical examination test, whose predictive value, in the case of general population is usually low. Higher specificity definitions will rely on appropriate symptoms and an abnormal nerve conduction study.4 The case criteria used in epidemiological studies needs to be consistent and reliable with good face validity. When applying different case definitions for CTS in a working population, a fair degree of agreement has been found, suggesting the possibility of pooling data from different studies.8 In aetiological studies as well as in workers’ surveillance, a broad case definition seems a preferable starting point, and then additional exploratory analyses on subsets of cases could be included in order to seek evidence of differential associations with risk factors and to set up tailored interventions.9

In spite of the imperfect alignment of symptoms and nerve conduction findings for CTS, our understanding of the relationship between symptoms, signs and nerve conduction studies is better for CTS than any of the other conditions raised,1 for example, cervical radiculopathy, brachial plexus neuropathy, and pronator teres syndrome. The diagnosis of definite CTS for epidemiologic or clinical use should rely primarily upon typical symptoms, for example, numbness, tingling, burning or pain in one or more of the first three digits, and a nerve conduction study that demonstrates slowing of median nerve conduction across the wrist.4 ,10 Other symptoms or signs, for example, ache or pain localised primarily to the palm, wrist or forearm; proximal muscle weakness; a dermatome pattern sensory loss; loss of deep tendon reflexes; and so on, should lead the physician away from CTS. The neurophysiological examination of a patient referred for CTS should consider symptoms that may arise from a more proximal site (eg, cervical radiculopathy, brachial plexus neuropathy).11

In conclusion, the evidence suggests that in epidemiologic studies, CTS can be accurately diagnosed and differentiated from other conditions by using an appropriate case definition and exclusion criteria.4 ,12 In the clinical setting, the outcome will depend on the need to make a specific diagnosis, and the clinician's approach to case management. If the approach is similar to that outlined above, there is no reason to suspect that CTS will be over-diagnosed.

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Footnotes

  • Contributors All the authors drafted, discussed and approved the manuscript.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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