Reliability of motor parameters for follow-up after local steroid injection in carpal tunnel syndrome

BACKGROUND: Local steroid injection is one of the treatment modalities for carpal tunnel syndrome (CTS). Symptomatic and electrophysiological improvement has been previously documented. The electrophysiological parameter, which represents the most consistent change after local steroid injection, is not well-known. OBJECTIVE: The objective of this study was to evaluate the changes in electrophysiological parameters 1 month after local steroid injection and to determine the parameter that is able to depict improvement across the severity spectrum of CTS. MATERIALS AND METHODS: Forty-seven patients (27 with bilateral disease, 74 hands totally) were included. The electrophysiological parameters studied at baseline included sensory onset latency, sensory nerve action potential amplitude, sensory conduction velocity (CV), distal motor latency, compound muscle action potential amplitude and motor CV. All patients were injected with 40 mg triamcinalone at the wrist. After 1 month, symptomatic improvement from baseline was documented using visual analog score of 100. Electrophysiology was repeated. Paired t tests were done between baseline electrophysiology parameters and those obtained 1 month after steroid injection for significant improvement. Subgroup analyses were performed in hands with mild to moderate (Grade 3 or less by Bland's classification) and severe disease (Grades 4 and 5). RESULTS: All patients showed a symptomatic improvement. Distal motor latency showed most consistent improvement irrespective of the severity of CTS. In mild to moderate CTS (Grade 3 or less of the classification given by Bland) sensory parameters were recordable and showed significant improvement in addition to distal motor latency. In the subcategory of severe CTS (Grades 4 and 5 of Bland) where sensory parameters are not recordable distal motor latency and the motor CV showed a significant improvement. CONCLUSION: One month after local steroid injection among the electrophysiological parameters studied distal motor latencies showed most consistent and recordable improvement across the severity spectrum of CTS. This can be used as a single objective parameter to follow-up patients after a local steroid injection to document improvement or relapse. They can also be considered as objective parameter to follow-up patients after surgery.