Neurophysiological classification of carpal tunnel syndrome: assessment of 600 symptomatic hands

Following the AAEM electrodiagnostic guidelines, we developed a neurophysiological classification of carpal tunnel syndrome (CTS). Six hundred hands with clinical CTS (mean age 51.4 yr., female/male ratio 5.5/1, right/left ratio 1.8/1) were prospectively evaluated and divided into six classes of severity only on the basis of median nerve electrodiagnostic findings: extreme CTS (EXT-absence of thenar motor responses), severe CTS (SEV-absence of sensory response and abnormal distal motor latency-DML), moderate CTS (MOD-abnormal digit-wrist conduction and abnormal DML), mild CTS (MILD-abnormal digit wrist conduction and normal DML), minimal CTS (MIN-exclusive abnormal segmental and/or comparative study), and negative CTS (NEG-normal findings at all tests). Using this neurophysiological classification, the CTS groups appeared normally distributed (EXT 3% of cases, SEV 14%, MOD 36%, MILD 24%, MIN 21%, NEG 3%), and the age of patients and clinical findings appeared to be related to neurophysiological abnormalities. Significant differences in median neurophysiological parameters not included in the classification (such as palm-wrist sensory conduction velocity) were observed in the different CTS groups. The analysis of the groups showed that: 1) the majority of advanced cases (SEV and EXT) occurred in older patients (60-80 years), 2) most of the milder cases (MIN and MILD) occurred in young female patients. The aim of this study was to standardise the neurophysiological evaluation of CTS.