Can studies of the second lumbrical interossei and its premotor potential reduce the number of tests for carpal tunnel syndrome?

Blood flow velocity but not tendon mechanics relates to nerve function in carpal tunnel syndrome patients

Carpal tunnel syndrome (CTS) develops from chronic compression of the median nerve. Chronic compression results in a number of vascular, structural and functional changes to the carpal tunnel tissues which ultimately manifest in the characteristic symptoms of CTS. The purpose of this study was to investigate the interplay of median nerve function, median nerve hemodynamics, and finger flexor tendon and subsynovial connective tissue (SSCT) mechanics in CTS patients. Thirty-five patients were recruited following nerve conduction study for this double-blinded imaging study. Ultrasound B-mode, pulse-wave Doppler, and colour Doppler images and videos were collected at the proximal carpal tunnel to quantify: (1) median nerve cross-sectional area, (2) intraneural blood flow velocity in 3 wrist postures (neutral (0°), flexion (15°), extension (30°)), and (3) flexor digitorum superficialis and SSCT displacement. Results demonstrate that intraneural blood flow velocity is dependent on median nerve function and wrist posture such that patients with mild CTS are more susceptible to the effects of non-neutral wrist postures. Tendon-SSCT mechanics do not appear to differ based on severity. This study stresses the importance of limiting exposure to non-neutral wrist postures in patients with early signs of the condition.

A new method to define cutoff values in nerve conduction studies for carpal tunnel syndrome considering the presence of false-positive cases

BACKGROUND

Nerve conduction studies (NCS) are useful tools for diagnosing carpal tunnel syndrome (CTS). Establishing the normal values is the first step required for utilizing NCS for diagnosis. Previous epidemiological studies demonstrated the presence of fairly large number of false-positive subjects regarding NCS among control population, which has not been properly considered in past studies. This study proposed a new method to address this issue.

METHODS

Non-diabetic 144 CTS patients were retrospectively enrolled using clinically defined inclusion criteria. Controls consisted of 73 age-matched volunteers without hand symptoms. Six NCS parameters were evaluated including peak-latency difference by the thumb method (thumbdif) and that by the ring-finger method (ringdif). The Youden index of the receiver operator characteristic curve was used both to judge the sensitivity of a parameter and to identify false-positive cases that were thought to have subclinical median neuropathy at the wrist. The linear function of six parameters was constructed, and the coefficient for each parameter was variously changed.

RESULTS

When the Youden index took on the maximum value, seven control subjects (10%) were identified as false-positive and were excluded from the calculation of normal values. The most sensitive parameter before exclusion was thumbdif, whereas ringdif became the most sensitive after exclusion. The cut-off value for ringdif was 1.15 ms before exclusion, but was 0.37 ms after exclusion.

CONCLUSION

This method can be widely applied to solve the statistical problem when the gold standard is lacking, and the outside reference standard is not completely reliable.

Lumbrical-interosseous recording technique versus routine electrodiagnostic methods in the diagnosis of carpal tunnel syndrome

Objectives

We aimed to evaluate the sensitivity of second lumbrical-interosseous (L-I) technique and to compare the results with other electrophysiological methods in patients with carpal tunnel syndrome (CTS).

Patients and methods

This cross-sectional study was conducted in an electrophysiology laboratory of a university hospital between January 2003 and January 2004. A total of 102 patients with CTS (174 hands) and 40 healthy controls (80 hands) were included. Median motor nerve conduction studies were obtained with recordings from the abductor pollicis brevis (APB), median sensory nerve conduction studies from digits I-III and at palm-wrist segment (P-W), median-ulnar sensory comparison at digit IV (M-U), and median-radial sensory comparison at digit I (M-R) were along with L-I technique.

Results

The highest sensitivities were found in the median sensory conduction velocity across the palm-wrist (88%), and digit I-wrist segments (80%), median motor distal latency over the APB (77%), and L-I study (76%). The specificities of conventional tests were higher than the sensitivity of L-I method (63%).

Conclusion

L-I method has a good diagnostic sensitivity in CTS; however, P-W, median sensory nerve conduction velocity at digit I and median distal motor latency are more sensitive than L-I method. Therefore, L-I method can be applied as a supportive technique in the evaluation of patients with CTS.

Practical approach to electrodiagnosis of the carpal tunnel syndrome: A review

Despite being the most common entrapment neuropathy and the most common reason for referral to the electromyography (EMG) laboratory, the diagnosis of carpal tunnel syndrome (CTS) continues to be challenging due to a large number of electrodiagnostic (EDX) tests available. We present a flowchart and propose a practical approach to the diagnosis of CTS using the available literature and the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) guidelines and the Practice Parameter for Electrodiagnostic Studies in Carpal Tunnel Syndrome.

Premotor potential study in carpal tunnel syndrome

INTRODUCTION

Premotor potentials (PMPs) precede compound muscle action potentials evoked from the second lumbrical muscle after median nerve stimulation. Although PMP has been identified as a median sensory nerve action potential, few reports have documented the significance of PMP parameters for diagnosing carpal tunnel syndrome (CTS).

METHODS

We investigated the relationships between PMP parameters and results of 6 standard median nerve conduction studies in 74 CTS hands.

RESULTS

Significant correlations were noted in all comparisons. PMP conduction velocity was strongly correlated with the sensory conduction velocity between wrist and digit 2 (r(2) = 0.91). Moreover, PMP parameters were significantly correlated with neurophysiological severity of CTS.

CONCLUSION

Measuring PMP parameters with a second lumbrical-interosseous study may be useful for diagnosing CTS.

The origin of the premotor potential recorded from the second lumbrical muscle in normal man

OBJECTIVE

When recording with a palm electrode, a premotor potential precedes the compound muscle action potential (CMAP), evoked from the second lumbrical (2L) muscle following median nerve stimulation. The purpose of this study was to determine the origin of the premotor potential from the 2L.

METHODS

We recorded potentials with multi-channel electrodes in the palm and finger in a bipolar or referential manner, stimulating the second digit or median nerve at the wrist.

RESULTS

We recorded the traveling nearfield sensory nerve action potential (SNAP) and stationary negative potential in the palm. The peak latency of the stationary negative potential was the same as the one of the near-field potential of the digital sensory fibers at the base of the second finger. The onset of the premotor potential from the 2L muscle is aligned to the palmar SNAP in a bipolar manner by antidromic stimulation.

CONCLUSIONS

We conclude that the premotor potential from the 2L muscle is composed of a SNAP arising from antidromically activated palm sensory branches and a far-field potential generated by the median digital nerve fibers as they pass from the palm into the second finger.

SIGNIFICANCE

Our results might be useful for evaluating the 2L-interossei test for diagnosing carpal tunnel syndrome.

[Diagnostic pitfalls in carpal tunnel syndrome]

BACKGROUND

This review focuses on the main aspects of positive and differential diagnosis of carpal tunnel syndrome (CTS) in different clinical situations encountered in daily practice.

STATE OF THE ART

Authentic CTS can be discovered in situations, which alter the usual presentation or therapeutic management. This is the case for instance in pregnant women or in the elderly subject or with acute motor forms where CTS discloses a focal intratunnel disorder (neuroma, lipoma, arterial condition, bone disorder) or a general disease (hereditary neuropathy, amylosis). In certain situations, the clinical manifestations suggest a more proximal compression of the medial nerve (round pronator, Struthers arcade, or superficial flexor) or an inflammatory condition (mononeuritis, inflammatory demyelinising neuropathy). Locoregional disease may also be involved, for instance a plexus (thoracobrachial outlet syndrome, post-radiation plexitis) or radicular condition. The clinical presentation of diffuse polyneuropathy with initial manifestations involving the upper limb (ganglioneuropathies, polyradiculoneuritis, small-fiber neuropathies) may also be misleading. Finally central conditions can sometimes be confused with CTS.

CONCLUSION

A rigorous physical examination and an electroneuromyogram are determining to avoid diagnostic pitfalls.

The significance of second lumbrical-interosseous latency comparison in the diagnosis of carpal tunnel syndrome

AIM

To assess the significance of the second lumbrical-interosseous latency (2LI-DML) comparison in the diagnosis of carpal tunnel syndrome (CTS).

PATIENTS AND METHODS

We examined 150 consecutive hands of patients referred with suspected CTS, using the 2LI-DML test and other standard measures of median nerve function. Correlations of the 2LI-DML test with standard tests were computed.

RESULTS

Hundred and four hands were electrophysiologically confirmed to have CTS. The 2LI-DML test was abnormal in 99/104 (95.2%) hands with CTS with a mean value of 1.54 +/- 1.12 ms. Among the other measures, the orthodromic median-ulnar palmar velocity comparison was the most frequently abnormal test (95/104 hands, 91.3%), followed by the double-peak morphology of orthodromic sensory action potential from digit 4 (94/104, 90.4%). The 2LI-DML test significantly correlated, either positively or negatively, with all other standard tests.

CONCLUSION

The 2LI-DML comparison is highly sensitive in diagnosing CTS, even in mild cases in which standard tests fail to detect abnormalities.

Sonography versus nerve conduction studies in patients referred with a clinical diagnosis of carpal tunnel syndrome

PURPOSE

To compare the diagnostic value of high-resolution ultrasound (US) with nerve conduction studies (NCS) in patients with clinically defined carpal tunnel syndrome (CTS).

METHODS

A prospective study was conducted on 66 consecutive patients investigated for sensory hand symptoms. The gold standard was the clinical diagnosis of CTS.

RESULTS

NCS showed greater diagnostic sensitivity (82%) than US (62%) in supporting a diagnosis of CTS. With increasing neurophysiologic severity of median neuropathy, there was increasing convergence of the two test methods. Abnormal US as the only diagnostic supportive evidence of CTS was rare. However, the positive predictive value of US for CTS was 100%.

CONCLUSION

NCS show better sensitivity than US in supporting a diagnosis of CTS. However, because of its high positive predictive value, one may consider using US as a screening test, eliminating the need for NCS in the majority of clinical suspicion of CTS and reserving NCS for cases in which US is negative.