A 48-year-old right-handed male surgeon complained of finger numbness, pain, cramps and weakness of 2 years’ progression, without improvement after 2 carpal tunnel corticosteroid injections and splinting. The patient was diagnosed with lacertus syndrome with Hagert’s triad. Sensory collapse test was positive, but the sensations during the test were not consistent with the literature. Therefore, a sensory collapse test was performed in combination with electromyography; immediately following cutaneous stimulation, partial transient collapse in muscle tone was observed, without complete interruption. Following surgical release of the ipsilateral median nerve at the lacertus fibrosus, the symptoms were resolved, and combined sensory collapse test and electromyography revealed minimal to no collapse in muscle tone following cutaneous stimulation.