Application of latent period of sensory nerve action potential in the ring finger for early diagnosis of carpal tunnel syndrome

ObjectiveTo explore the sensitive electrophysiological index in the diagnosis of carpal tunnel syndrome (CTS) in early stage.MethodsThirty eight patients with clinical confirmed CTS and normal latency of motor action potential in the distal median nerve were involved in the study. The latency of sensory nerve action potential (SNAP) in the median nerve and ulnar nerve in the ring finger were recorded and compared with those in 46 normal control subjects.ResultsThe abnormal rate of sensory nerve conduction velocity (SNCV) in the median nerve in CTS group was 68%. The abnormal rate of the difference of the latent period of SNAP between median and ulnar nerve in the ring finger was 91% (≥0.4ms). After stimulation of the ring finger, double spike potential was recorded in the median nerve at the wrist in 16 patients with CTS, but not found in the control group.ConclusionThe difference (≥0.4ms) of latency of SNAP between the median and ulnar nerve in the ring finger is a sensitive index for the diagnosis of CTS in early stage and should be used as a routine method in electromyography.