Long term effect of local corticosteroid injection for carpal tunnel syndrome: a relation with electrodiagnostic severity.

OBJECTIVE: Carpal tunnel syndrome (CTS) is a common entrapment neuropathy. A local corticosteroid injection at the carpal tunnel inlet is often given to reduce the signs and symptoms. The long term effect of a local corticosteroid injection is not known yet. The aims of the study were to assess the long term effect of a local corticosteroid injection and the rognostic factors.

METHODS: Assessment of 419 consecutive patients, seen between November 2004 and November 2007 at our Neurology out-patient clinic. After confirmation of the diagnosis CTS the treating neurologist decided on the patients eligibility for a local corticosteroid injection, containing 40 mg methylprednisolone.

RESULTS: Local corticosteroid injection was given to 273 of the 419 patients with CTS (65%), 122 (29%) were treated surgically and 24 (6%) were treated by another therapy. Of the 273 patients long term follow-up was available for 211 (77%) patients. A beneficial effect of more than 6 months was seen in 132 patients (63%), longer than 12 months in 102 patients (48%), and longer than 18 months in 71 patients (34%). Only severity of electrodiagnostic testing was a predictor of outcome. The median time until treatment failure was 15 months for mild, 5 months for moderate and 4.5 months for severe CTS (logrank test p=0.02).

CONCLUSION: Patients with an electrodiagnostically mild CTS (i.e., abnormal comparative tests or prolonged median DSL>3.5 ms but normal median DML) are good candidates for a local steroid injection with 50% having a good long term effect for more than 15 months.

SIGNIFICANCE: This study shows that the EMG severity of CTS is an important prognostic factor for the long term effect of a local steroid injection.