Diagnostic value of quantitative sensory testing (QST) in carpal tunnel syndrome

The initial sensory symptoms of carpal tunnel syndrome (CTS) are usually intermittent and the clinical neurological examination is often normal. The aim of the present study was to determine the rate of impairment of different somatosensory modalities in CTS by means of the following tests: vibrametry, tactile pulses, von Frey hairs, two-point discrimination (2-PD), graphesthesia and warm and cold perception thresholds. The material consisted of 33 hands with CTS from 22 patients. Each of the first 3 tests was abnormal with elevated thresholds in 17 CTS hands (52%), 2-PD was abnormal in 10 hands (30%), graphesthesia in 8 hands (24%), and warm and cold thresholds in only 5 hands (15%). There was an overlap so that at least one test was abnormal in 27 of the 33 CTS hands (82%). Thus, impairment of sensibility can be demonstrated in a majority of patients with CTS if more than one test is applied. Vibrametry and von Frey hairs are recommended instead of the commonly used 2-PD, since abnormality was more often revealed and since they are equally easy to apply. No individual test was sensitive enough to qualify as a diagnostic criterion when it was applied with the hand in resting position. A significant increase in both sensitivity and specificity can be expected for any test if it is combined with provocation, such as wrist flexion, as has been demonstrated for vibrametry.