Differential sensory involvement of digits II, III and IV in carpal tunnel syndrome patients

Abstract EN

Background : conduction studies of the digital sensory branches of the median nerve have been shown to vary considering the degree of conduction slowing in carpal tunnel syndrome (CTS) patients.

We observed that subsets of patients may show homogenous involvement or alternatively may show differential involvement of the digital sensory branches of the median nerve among CTS patients.

Objective : investigate the differential involvement of the digital sensory branches of the median nerve in CTS.

Methodology : one hundred and seven hands from 85 CTS patients together with 45 hands of 35 healthy matched control subjects.

Anhidrotic sensory conduction studies of the index, middle and ring median nerve digital sensory branches, standard motor conduction study for the median nerve, and anhidrotic sensory conduction study of the ulnar nerve to the ring finger.

Sensory conduction velocity to the onset, peak sensory latencies and distal motor latency were measured.

The differences of peak sensory latencies of the digital branches were measured, a sum of difference (sumdiff) variable was calculated to reflect homogenous and non-homogenous digital sensory involvement using a cutoff point of normal = mean2SD = 0.7 ms, obtained from normal control measurements.

Results : there was a statistically significant difference of the sensory variables between the studied digital sensory branches, with maximum difference showed between the index and the ring finger, among the studied patients.

Patients showed approximately 3 : 1 ratio between those with non-homogenous and homogenous involvement.

The mean sendoff in the first subset was 6 times that in the homogenous sensory involvement group.

A trend towards higher incidence of non-homogenous sensory affection was relatively demonstrated more among the severer category of DML involvement, however, the association was not conclusively firm.

The sendoff was positively correlated with distal motor latency (DML).

The ring finger showed the worst conduction parameters.

Discriminant analysis revealed that the variables with best ability to classify patients according to level of severity of DML affection were peak sensory latency (PSL) and sensory conduction velocity to middle finger.

The sendoff was a significant discriminator variable but not as strong as the sensory variables of the middle finger.

Conclusion : CTS patients may be allocated to either a subset with non-homogenous or a subset with homogenous affection of the digital sensory branches of the median nerve.

This finding may require further study to identify the factors behind such allocation.

However, the sizeable non homogenous affection of digital sensory branches emphasizes the need to consider combined sensory involvement of the digital branches when the sensory variable is considered in scales of CTS severity.

The distinctive involvement of the ring finger may justify a recommendation to consider it for CTS screening.