Thenar motor neuropathy electrophysiological study of 28 cases

"Million dollar nerve" magnetic resonance neurography: first normal and pathological findings

OBJECTIVES

To evaluate prospectively the feasibility of magnetic resonance neurography (MRN) in identifying the anatomical characteristics of thenar muscular branch (TMB) of the median nerve, also known as the "million dollar nerve," in patients and controls.

METHODS

Thirteen patients affected by carpal tunnel syndrome (CTS) and four healthy controls had their hands scanned on a 3-T MR imaging scanner for TMB visualization. Median nerve anatomical variations were classified into four groups according to Poisel's classification system modified by Lanz. TMB signal intensity and diameter were assessed for the diagnosis of neuropathy.

RESULTS

TMB was successfully identified in all patients and subjects by using MRN. The most suitable pulse sequences to identify and measure nerve diameter were 3D DW-PSIF and T2-FS-TSE. The axial oblique and sagittal oblique planes are complementary in demonstrating its entire course. TMB had mostly an extraligamentous course with radial side origin (93.8%, each). All patients experienced increased T2 signal intensity (p < 0.001) and thickened nerves. Mean TMB diameters were 1.27 ± 0.21 mm (range, 1.02-1.74 mm) and 0.87 ± 0.16 mm (0.73-1.08 mm) (p = 0.008) in the patient and control groups, respectively.

CONCLUSION

MRN is a reliable imaging technique for identification and anatomical characterization of TMB in patients affected by CTS. This innovative imaging workup may therefore be included in the preoperative evaluation of patients scheduled for carpal tunnel release, especially in CTS with TMB involvement or even in isolated TMB neuropathy.

KEY POINTS

• Magnetic resonance neurography allows precise visualization of the thenar muscular branch of the median nerve. • Thenar muscular branch anatomical variations can be correctly identified. • Preoperative scanning can contribute to reducing the risk of iatrogenic injuries during carpal tunnel release, especially in carpal tunnel syndrome with thenar muscular branch involvement or even in isolated thenar muscular branch neuropathy.

Sustained atypical myokymia of the abductor pollicis brevis with a focal slowing of the median nerve motor axons at the wrist

OBJECTIVE

We report a case of sustained atypical myokymia associated with short bursts of neuromyotonic discharges involving the abductor pollicis brevis (APB) muscle and describe a useful way of detecting a focal slowing involving a small number of median nerve motor fibers with a concentric needle using the filter setting for single fiber electromyography (EMG).

METHODS AND RESULTS

A 62-year-old woman developed right thumb twitches at regular interval of 1.7-3.3 s (0.6-0.3 Hz), which continued for more than four months. Muscle twitches remained the same during altered hand position, psychological stress, or sleep. A concentric needle inserted in the active zone of the APB muscle revealed myokymic bursts with a characteristic of neuromyotonic discharges. Inching study, stimulating at 5 mm increment along the median nerve and recording with a concentric needle using a filter setting for single fiber EMG, revealed a focal slowing of the motor fibers at a point 5-10 mm distal from the distal crease of the wrist, an entrapment site occasionally seen in the carpal tunnel syndrome. One injection of botulinum toxin type A eliminated the myokymia, which then recurred two and a half years later, showing less prominent muscle twitches.

CONCLUSIONS

Sustained atypical myokymia seen in our case represented bursts of neuromyotonic discharges originated from a focal demyelinating lesion involving a few median nerve motor fibers.

Intrarater and interrater reliability of a hand-held dynamometric technique to quantify palmar thumb abduction strength in individuals with and without carpal tunnel syndrome

STUDY DESIGN

Clinical measurement.

INTRODUCTION

Individuals with carpal tunnel syndrome (CTS) sometimes exhibit weakness of palmar abduction strength (TAS). Reliable assessment of this strength in both subjects with and without CTS with the commonly available Microfet 2 is not known.

PURPOSE OF THE STUDY

The purpose of this study was to determine the intrarater and interrater reliabilities of a handheld dynamometric (HHD) method to assess TAS in individuals with and without CTS using the commercially available MicroFET2 and to examine the association between TAS in individuals with CTS and the Carpal Tunnel Symptom Questionnaire (CTSQ) scores.

METHODS

In 2 different study phases, individuals with and without CTS were assessed for TAS by 2 different examiners. The CTSQ was administered to the individuals with CTS.

RESULTS

Intrarater and interrater reliability coefficients (0.89-0.93 and 0.82-0.90, respectively) were excellent in individuals with and without CTS. Weak negative correlations were found between TAS and overall CTSQ and symptom severity subscale scores, and a moderate negative correlation was found between TAS and functional Status Subscale score.

DISCUSSION

This HHD method of reliably assessing TAS better quantifies deficits and progress than traditional manual muscle testing for muscle grades greater than 3/5.

CONCLUSION

This method of HHD reliably quantifies TAS but is more reliable with the same than different raters.

Motor Examination in the Diagnosis of Carpal Tunnel Syndrome

The relative importance and use of motor evaluation to diagnose carpal tunnel syndrome (CTS) is not clear. Because the ulnar nerve is not affected in CTS, we evaluated comparing the strength of the median-nerve innervated muscles to the ulnar innervated muscles in the same patient, through manual muscle testing (MMT) and a handheld dynamometer. Our purpose was to evaluate whether this method, which takes into account patient-dependent factors that would affect both groups of muscles equally, can provide better assessment of CTS. A retrospective case-control review of MMT and dynamometer-measured strength for CTS was performed. The study was performed retrospectively but prior to surgery or other treatment. There were 28 cases (CTS) and 14 controls (without CTS). Positive nerve conduction tests defined cases. MMT of the thenar musculature was found to be unreliable as a test for CTS. Comparisons to ulnar nerve innervated muscle strength did not improve sensitivity or specificity of the MMT examination. Use of the dynamometer improved sensitivity and specificity of motor testing in CTS over MMT. Motor evaluation is important for the diagnosis of CTS, but further study is warranted, specifically to define the method of motor evaluation and delineate the subgroup of patients (predominantly thenar motor presentation) that would benefit most from motor testing and motor-focused treatment.

High-resolution ultrasound visualization of the recurrent motor branch of the median nerve: normal and first pathological findings

Purpose

To evaluate in a prospective study the possibility of visualization and diagnostic assessment of the recurrent motor branch (RMB) of the median nerve with high-resolution ultrasound (HRUS).

Materials and methods

HRUS with high-frequency probes (18–22 MhZ) was used to locate the RMB in eight fresh cadaveric hands. To verify correct identification, ink-marking and consecutive dissection were performed. Measurement of the RMB maximum transverse-diameter, an evaluation of the origin from the median nerve and its course in relation to the transverse carpal ligament, was performed in both hands of ten healthy volunteers (n = 20). Cases referred for HRUS examinations for suspected RMB lesions were also assessed.

Results

The RMB was clearly visible in all anatomical specimens and all volunteers. Dissection confirmed HRUS findings in all anatomical specimens. Mean RMB diameter in volunteers was 0.7 mm ± 0.1 (range, 0.6–1). The RMB originated from the radial aspect in 11 (55%), central aspect in eight (40%) and ulnar aspect in one (5%) hand. Nineteen (95%) extraligamentous courses and one (5%) subligamentous course were detected. Three patients with visible RMB abnormalities on HRUS were identified.

Conclusion

HRUS is able to reliably visualize the RMB, its variations and pathologies.

Key Points

• Ultrasound allows visualization of the recurrent motor branch of the median nerve.

• Ultrasound may help clinicians to assess patients with recurrent motor branch pathologies.

• Patient management may become more appropriate and targeted therapy could be improved.

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-016-4671-1) contains supplementary material, which is available to authorized users.

Prevalence of Asymptomatic Neurophysiological Carpal Tunnel Syndrome in 130 Healthy Individuals

Diagnosis of carpal tunnel syndrome (CTS) is frequently confirmed by performing nerve conduction studies. Previous studies demonstrated that abnormal nerve conduction study (NCS) is suggestive of CTS among asymptomatic individuals. However, previous studies included individuals with risk factors for the syndrome. A NCS was performed on the median and ulnar nerves in 130 healthy individuals. About 15% of individuals in this study demonstrated electrodiagnostic evidence of carpal tunnels syndrome. Four cases have shown signs of isolated median neuropathy with normal median sensory component. Results indicated that the most widely used method for confirming diagnosis of CTS may have up to 15% of false positives. However, most of those showed changes of minimal CTS. Isolated prolongation of the median motor latency should be investigated further as they are usually classified as moderate to severe CTS and may undergo unnecessary surgeries.

Relation between distal motor latency delay and sensory action potential absence of the median nerve in carpal tunnel syndrome

OBJECTIVE

To elucidate the cutoff value for distal motor latency (DML) at which sensory nerve action potentials (SNAPs) are absent in carpal tunnel syndrome (CTS) patients.

METHOD

We examined 157 hands in 129 patients with CTS retrospectively. We classified the patients according to whether SNAPs were successfully obtained. Group A consisted of hands with SNAPs, while Group B consisted of hands without SNAPs. The cutoff value for DML was determined by receiver-operating characteristic curve analysis. We enrolled 130 hands with CTS for the analysis, because measurements were successful in 130 hands for compound muscle action potentials and in 82 hands for SNAPs from a total of 157 hands investigated.

RESULTS

A significant correlation was observed between DML and SCV (P<0.0001, R*2=0.40). The most discriminative cutoff value for DML was 7.7ms, resulting in a sensitivity of 79.6% and specificity of 79.3%.

CONCLUSION

Cases in which SNAPs are evoked despite a DML longer than 7.7ms should raise suspicion.