Comparison of sensitivity of lumbrical and interossei latency recording and standard median nerve conduction studies in electrodiagnosis of carpal tunnel syndrome

Abstract EN

Hypothesis : carpal tunnel syndrome (CTS) is the most widely known entrapment neuropathy.

Electrophysiological procedures e.g., nerve conduction studies (NCSs) are of established value in the diagnosis of CTS and can confirm the clinical diagnosis in the majority of patients.

It also detects an incidental finding in some asymptomatic subjects.

One must therefore carefully check the test results and the clinical findings before resorting to surgical intervention.

However, there are patients with symptoms and signs suggestive of CTS who remain difficult to diagnose with standard electro diagnostic tests.

A variety of NCSs have been employed to demonstrate patients with mild CTS.

The lack of sensitivity of distal motor latency (DML) may be due to either to sparing of motor as compared to sensory fibers or to the inability of standard median motor studies to detect an abnormality.

Objective : to demonstrate early and mild CTS and compare sensitivity of standard median NCSs with 2nd numerical and interpose latency differences using the same active recording electrode placed over the motor point of 2nd numerical lateral to the 3rd metacarpal with stimulation of median and ulnar nerves at wrist at equal distances.

Methodology : this study included 40 normal control hands and 61 patients hand with CTS; the control group was 14 males and 28 females; their mean age was 39.5 years (yrs) ? 9.9 SD, ranged from 21 to 56 yrs.

The patients group included 61 patient hands with clinical signs and symptoms suggestive of CTS (i.e., parenthesis in the median nerve distribution, nocturnal symptoms, intermittent wrist and arm pain, positive Tinsel's and Halen's signs, etc...).They were subsequently proven to have CTS with electrophysiological median nerve standard NCSs; they were 15 males and 46 females, their mean age was 45 yrs ± 10.8 SD, and their age ranged from 28 to 63 yrs.

All subjects were subjected to electrophysiological standard median NCSs e.g., DML to abductor policies braves (APB), median nerve Anhidrotic distal sensory latency (ADSL) to index finger, median and ulnar ADSL differences to ring finger, and compared with 2nd numerical and interpose latency differences.

Results: A prolonged 2nd numerical – interpose latency differences > 0.4 msec was found to be a sensitive indicator of CTS in all patients; the sensitivity of the 2nd numerical-interpose latency difference (96 %) was higher than the highest sensitive test of standard median NCSs (Median– Ulnar ADSL difference) (89 %).

CTS patients were divided into Grade 1.

Very mild CTS, Grade 2.

Mild CTS, Grade 3.

Moderate CTS, Grade 4.

Severe CTS and possible CTS; the sensitivity or percentage of abnormal 2nd lumbrical-interossei latency differences was 80 %, 87 %, 95 %, 100 % and 67 %, respectively.

Conclusions : thus, the more sensitive the study needed to demonstrate the CTS, the more severe the CTS was graded.

The comparison of 2nd numerical and interpose latency differences is a sensitive measure technique can help and demonstrate early and mild CTS patients as it is safe, simple and easy to perform in any electrophysiology laboratory.

We provide the evidence of 2nd lumbrical-interossei latency differences that could be a standard technique for electro diagnosis of CTS.