The optimum hand temperature to study nerve conduction in patients with carpal tunnel syndrome

To define the skin temperature at which diseased nerves are better differentiated from the healthy. Motor and sensory conduction of median and ulnar nerve were evaluated in 52 patients with carpal tunnel syndrome (CTS) and 52 matched healthy controls at environmental skin temperature (mean 32-33 °C), after warming by an average of 2 °C and cooling to approximately 6 °C below baseline. In the hot condition, group comparisons for the median nerve showed a similar rate of distal motor latency (DML) reduction and sensory conduction velocity (SCV) increase in CTS and controls. With cold, the rate of change was smaller for the patients: DML mean increase was 5% /°C (7% for controls) and SCV mean decrease was 2.5%/°C (3.2% for controls). Individual patients' analysis revealed fewer abnormal median DML and SCV values at hot or at cold, compared to environmental temperature. It is concluded that conduction adjustments for low hand temperatures based on healthy measurements resulted in overcorrection and therefore underdiagnosis of CTS. Alternatively, at excessive hand warming the convergence of patient and healthy measurements also lead to underdiagnosis. Maintenance of skin temperature at 32-33 °C, corresponding to normal body temperature, is the optimum approach and should always be employed in clinical practice.