- Objective: To evaluate the clinical and electrophysiological effects of local depo-methylprednisolone injection in patients with carpal tunnel syndrome (CTS) over a 6-months period. Methods: Twenty one patients, of whom 7 were lost for follow-up (mean age 57.9 ± 8.4) with clinical and electrophysiological evidence of CTS were treated by injection of depo-methylprednisolone 40 mg proximal to the carpal tunnel. Severity of pain (VAS), rates of numbness/paresthesias and nocturnal awakening, motor and sensory nerve conduction studies were used as outcomes. All tests were performed before, 1, 3 and 6 months after the injection. Results: Severity of pain was significantly reduced at all follow-up time points ( p< 0.001). Prior to injection all patients complained of night pain and awakening. On the first, third and sixth months, 0(0%), 4 (29%) and 7 (50%) of the patients, respectively, had night awakening. All patients complained of numbness before the treatment. This symptom disappeared in 81% of the patients after one month and reappeared in all after three months. Significant improvement was shown in the mean distal motor latency (DML) of the median nerve: 5.2 ± 0.9 msec. before, 4.6 ± 0.6 msec. and 4.7 ± 0.6 msec. 1 and 3 months after the injection, respectively ( p< 0.05). Mean values of motor muscle potential amplitudes, sensory latency and sensory amplitude did not change significantly after the treatment. Conclusions: Local corticosteroid injection for the treatment of CTS provides significant symptom improvement for three months. No electrophysiological parameters were improved after injection, except the improvement in distal motor latency of the median nerve.