According to median sensory nerve action potential onset-latency to index finger in a 140 mm fixed distance, 993 carpal tunnel syndrome (CTS) hands from 668 patients were grouped into MIld (3.0 to 3.5 ms, 384 hands), MOderate (3.6 to 4.4 ms, 332 hands), SEvere (> 4.4 ms, 135 hands) and UNrecordable (142 hands) and correlated with CTS symptomatology duration. All patients have sensory antidromic median-radial latency difference (MRD) e > or = 1.0 ms without any doubt about CTS diagnosis. Patients with systemic disease, trauma or previous surgery were excluded. There is a remarkable cumulative percentage increase from 1 to 12 months in group UN (3.5% to 38.7%, 11 folds), much less than the group MI (13.8% to 54.6%, 3.9 folds). There is also a remarkable non-cumulative percentage increase in group UN, from 1 to 4-12 months; the group MI had a relatively uniform distribution in all symptomatic duration groups from 1 to > 60 months. The conclusion is that median nerve compression at carpal tunnel can lead to unrecordable potentials in a relatively short period from 1 to 12 months of evolution, suggesting acute/subacute deterioration. Electrophysiological evaluation must be done periodically in patients that underwent clinical treatment, since cumulative 38.7% of group UN was found in 12 months period.
carpal tunnel syndrome; median nerve; compression neuropathy; nerve conduction study
