The Scratch-Collapse Test: Are Electrodiagnostic Changes Measurable?

Carpal tunnel syndrome is commonly managed by hand and upper extremity surgeons. Though electrodiagnostics are considered the gold standard diagnosis, the scratch collapse test (SCT) was introduced to address uncertainty, despite remains controversial. To address this, we sought to identify if the SCT can correlate with EDS studies if the SCT can identify actual changes in measures of nerves.

We reviewed patients who underwent electrodiagnostic studies (EDX) and SCT for carpal tunnel syndrome (CTS). Demographic data as well as sensorimotor amplitudes, latencies, and velocities on nerve conduction and electromyography were collected. Analogous values based on SCT findings were analyzed for statistical significance.

Three hundred fifty patients with CTS were included. Sensory and motor velocities and amplitudes were significantly lower in patients with a positive SCT. Motor values were independent of age, though younger patients had larger measured changes. Obese patients did not show any motor EDX changes with the scratch collapse test, though thinner patients did. All changes were seen in nerve conduction only.

Carpal tunnel can be a difficult problem to diagnose as one study does not singularly determine the condition. The SCT was introduced to facilitate easier diagnosis. We demonstrate that the SCT correlates with changes on nerve conduction studies, especially in relation to decreased amplitudes and velocities, suggesting that it does identify changes in nerve with compression, specifically axonal, and myelin damage. These findings support the use of the SCT maneuver to evaluate and diagnose in appropriate patients.