Doctor update guide on nerve conduction studies for carpal tunnel syndrome
The role of nerve conduction studies in the diagnosis and management of carpal tunnel syndrome.
Nerve conduction studies are an extremely frequently used investigative tool to aid the diagnosis of carpal tunnel syndrome. The studies involve trans-cutaneous stimulation of median and ulnar motor and sensory (and sometimes radial sensory) nerves across the wrist. The aim of the study is to attempt to demonstrate a delay or a reduction in nerve conduction velocity of median motor or sensory nerves, either absolute or importantly relative to ulnar nerve velocities, across the wrist in cases of carpal tunnel syndrome. A positive nerve conduction study result may then be used to classify the electrophysiological severity of the median entrapment with evidence of motor involvement being seen in cases of moderate and severe carpal tunnel syndrome.
Although there is some controversy regarding the role of nerve conduction studies in carpal tunnel syndrome, particularly in patients with a classical clinical history/examination and no confounding factors such as diabetes, previous surgery/trauma etc, the investigation an extremely useful tool for both diagnosis and management. As with the majority of investigations for any medical condition, the results of nerve conduction studies in carpal tunnel syndrome are associated with both false positive and false negative rates. Although it is difficult to precisely quantify the false negative rate, due partly to the lack of a precise 'gold-standard' definition of carpal tunnel syndrome and whether or not more sensitive nerve conduction study tests are employed, it is probably in the region of 2-8%. A positive nerve conduction study for carpal tunnel syndrome test does however provide an extra robust layer of evidence and reassurance about the diagnosis. In addition to this there is little doubt that the investigation is of significant importance in the following situations.
1) Nerve conduction studies are highly useful in providing evidence for carpal tunnel syndrome in patients with atypical symptoms and those with other potential explanations for apparent median nerve distribution symptoms. A clear example would be a patient with a degree of neck pain or stiffness in who the diagnosis of a C6 or C7 radiculopathy could be suspected. Another, perhaps less well recognised, example would be an individual who could potentially have a work related upper limb disorder (e.g. repetitive strain injury) which may be associated with sensory symptoms such as parasthesia as well as pain.
2) As well as being useful for the diagnosis of carpal tunnel syndrome pre-operative nerve conduction study results are extremely valuable in planning treatment in patients with residual symptoms following decompressive surgery. Nerve conduction study findings of a deterioration or lack of any improvement when compared to pre-surgical findings provide fairly strong evidence of persistent or recurrent carpal tunnel syndrome as the cause of on-going symptoms.