Diagnostic specificity of sensory and motor nerve conduction variables in early detection of carpal tunnel syndrome

Near-nerve versus surface electrode recordings of sensory nerve conduction in patients with carpal tunnel syndrome

OBJECTIVES

The aim of the study was to compare the relative sensitivity of sensory nerve conduction (SNC) recorded with near-nerve needle electrodes and SNC recorded with surface electrodes in demonstrating focal slowing of the median nerve in patients with symptoms of carpal tunnel syndrome (CTS).

MATERIALS AND METHODS

Eighty-two consecutive patients with clinical symptoms and signs of CTS were studied prospectively by the same clinical neurophysiologist. Orthodromic near-nerve recording from digits 1 and 3, distal motor latency, and antidromic surface recording from palm to digit 2 and wrist to digit 2 were performed in all patients. Near-nerve recording of the ulnar nerve was done in patients with abnormal median nerve conduction. Patients were compared to controls.

RESULTS

Near-nerve SNC was abnormal (slowed velocity or absent response) in 52% of the patients from digit 1 to wrist, in 51% from digit 3 to wrist, and 40% had a prolonged distal motor latency. Surface antidromic SNC was abnormal in 49% from wrist to palm, and in 43% from wrist to digit 2. Statistical analysis revealed no significant difference between the near-nerve method and the surface method. Absent sensory potentials were more common with the surface method.

CONCLUSION

As a routine study of CTS patients, the surface technique can be used and the near-nerve technique merely used for patients with absent surface responses.

Requests for electromyography from general practitioners and specialists: critical evaluation

In order to improve the quality of service and limit costs of a local electromyographic service, the requests for electromyographic (EMG) examination issued by general practitioners and specialists were critically evaluated. The diagnoses suspected by referring doctors were compared with medical history and clinical data to analyze (1) the utility of EMG for the final diagnosis and (2) the concordance with that of the neurophysiologist and with the EMG results. In 1994 and 1995, there were 3482 patients referred to the EMG service. Only patients undergoing EMG for the first time (2706 subjects) were considered. In 76.6% of cases, the referring doctor had indicated the suspected diagnosis in the request. This diagnosis was compatible with medical history, symptoms and the results of neurological examination in 57.6% of cases. In 77.2%, the neurophysiologist considered the EMG useful in confirming the clinical diagnosis. The suspected diagnosis was confirmed by the clinical diagnosis of the neurophysiologist and by the EMG results in 54.2% and 45.4% of cases, respectively. When the request was issued by neurosurgeons, neurologists, orthopedists, rheumatologists and physiatrists, the suspected diagnosis was more accurate; as a consequence the EMG was more correctly oriented than when the request was issued by other specialists or by general practitioners. It is recommended that neurological examination be a prerequisite for EMG requests issued by general practitioners.

Electrophysiological studies in mild idiopathic carpal tunnel syndrome

Many techniques have been reported to improve the diagnosis of carpal tunnel syndrome (CTS), but there is no agreement on the diagnostic yield of these different methods. We used an electrophysiological protocol including the assessment of the orthodromic sensory conduction velocity of the median nerve along the carpal tunnel, comparison of median and ulnar sensory conduction between the ring finger and wrist, short segment incremental median sensory nerve conduction across the carpal tunnel recording from the III digit ('inching test'), the study of the refractory period of transmission (RPT) and calculation of the distoproximal ratio obtained by dividing the nerve conduction velocity in the median nerve between the third digit and the palm and between the palm and wrist in 41 patients with mild CTS (75 symptomatic hands) and in 45 control subjects. The distoproximal ratio calculation was the most sensitive technique (81%), but was also the least specific. The 'inching test', even though less sensitive, had the advantage of localising focal abnormalities of the median nerve along the carpal tunnel. RPT was abnormal in patients with recent symptoms. Combining the different techniques, an overall sensitivity of 92% was reached, 11% higher than the yield of the single best test suggesting that a multimodal approach could be useful. The best procedure for electrodiagnosis of mild CTS was to combine the median/ulnar comparison test with calculation of the disto-proximal ratio.

Conduction block and segmental velocities in carpal tunnel syndrome

In carpal tunnel syndrome (CTS) standard measurement of median distal motor latency and sensory conduction does not distinguish whether low amplitude responses are due to axonal degeneration or demyelination. In 88 control and 294 CTS hands we recorded amplitude and duration of compound muscle action potential (CMAP) and of antidromic sensory nerve action potential (SNAP) after palm and wrist stimulation to determine wrist to palm amplitude, duration ratios and segmental conduction velocities. In 16% of CTS hands there was an abnormal amplitude reduction without increased duration of CMAP or SNAP from wrist stimulation indicating partial conduction block. In 148 hands distal motor latency to abductor pollicis brevis and/or sensory conduction to digit 2 were abnormal. In the remaining 146 hands wrist to palm motor conduction was less than 35 m/s in 22.6% and wrist to palm sensory conduction was less than 45 m/s in 13%. At least one segmental conduction was abnormal in 27% of hands. Segmental studies allow the discrimination between conduction block and axonal degeneration, increase diagnostic yield in CTS, and might be useful in addressing treatment and predicting outcome.

Neurophysiological classification of carpal tunnel syndrome: assessment of 600 symptomatic hands

Following the AAEM electrodiagnostic guidelines, we developed a neurophysiological classification of carpal tunnel syndrome (CTS). Six hundred hands with clinical CTS (mean age 51.4 yr., female/male ratio 5.5/1, right/left ratio 1.8/1) were prospectively evaluated and divided into six classes of severity only on the basis of median nerve electrodiagnostic findings: extreme CTS (EXT-absence of thenar motor responses), severe CTS (SEV-absence of sensory response and abnormal distal motor latency-DML), moderate CTS (MOD-abnormal digit-wrist conduction and abnormal DML), mild CTS (MILD-abnormal digit wrist conduction and normal DML), minimal CTS (MIN-exclusive abnormal segmental and/or comparative study), and negative CTS (NEG-normal findings at all tests). Using this neurophysiological classification, the CTS groups appeared normally distributed (EXT 3% of cases, SEV 14%, MOD 36%, MILD 24%, MIN 21%, NEG 3%), and the age of patients and clinical findings appeared to be related to neurophysiological abnormalities. Significant differences in median neurophysiological parameters not included in the classification (such as palm-wrist sensory conduction velocity) were observed in the different CTS groups. The analysis of the groups showed that: 1) the majority of advanced cases (SEV and EXT) occurred in older patients (60-80 years), 2) most of the milder cases (MIN and MILD) occurred in young female patients. The aim of this study was to standardise the neurophysiological evaluation of CTS.

[Critical study of electrophysiologic techniques for exploration of carpal tunnel syndrome]

Carpal tunnel syndrome is the most frequent entrapment neuropathy. Nerve conduction studies and electromyography are useful to appreciate the localization and the degree of nerve involvement, and help to the therapeutic management. Various electrophysiological procedures may be used and are reviewed. For each of them, positive (sensitivity and specificity) and negative points (technical difficulties, errors and false positive) are reported. A guideline is proposed.

Comparison of techniques for detecting digital neuropathy

A complication of endoscopic carpal tunnel release (6/53 consecutive cases) is rupture of a digital branch. The objective of this study was to find a method for detecting neuropathy of the digital branch innervating the radial side of the fourth digit and the ulnar side of the third digit. This study examined whether the following sensory nerve conduction techniques would enhance diagnosis of this neuropathy: (1) recording with standard digital ring electrodes; (2) recording with ring electrodes from two adjacent fingers; and (3) disc electrodes placed between two fingers. Ten healthy individuals were studied before and after lidocaine anesthesia of the digital branch between the ring and middle finger. Statistical analysis was performed with a two-tailed, paired t test. Results show that after lidocaine injection there was a decrease in antidromic amplitude of 94% for ring electrodes on the fourth digit, 62% for rings on the third digit, 77% for disc electrodes between the fourth and third digits, and 74% for rings on digits 4 and 3 (P < 0.005), with no significant change in peak latency (P > 0.3). In conclusion, although all techniques used in this model yielded a significant change in amplitude, rings on the third digit compared with the second and discs between digits 4/3 compared with 3/2 were most specific without false-positives from normal data. It is hoped this study will aid the electromyographer in postoperative diagnosis.

AAEM case report #2: the carpal tunnel syndrome

The symptoms and signs which constitute the carpal tunnel syndrome (CTS) result from entrapment or compression of the median nerve within the carpal tunnel. Electrodiagnostic studies may objectively document the presence of median neuropathy within the carpal tunnel and help distinguish CTS from other disorders such as cervical radiculopathy, neurogenic thoracic outlet syndrome, proximal median nerve compression syndromes, and polyneuropathy which may either mimic or occasionally coexist with CTS. Recording median nerve responses with wrist and palm stimulation allows determination of the wrist segment conduction velocity which is a more sensitive nerve conduction parameter than wrist latency measurements. Electrodiagnostic testing permits estimation of severity and relative contribution of axonal versus demyelinative nerve injury. This information can provide prognostic information and help guide therapeutic decisions.

Sensory neural conduction of median nerve from digits and palm stimulation in carpal tunnel syndrome

The median sensory nerve conduction between ring finger and wrist is a suitable parameter for early detection of carpal tunnel syndrome (CTS), although shorter segments of median nerve have also been proposed for the same goal. In order to assess the relative diagnostic value of the sensory nerve conduction velocity (SNCV) of the third palmar branch versus the SNCV of the second palmar branch, generally performed until now, we studied 62 patients with typical signs and symptoms of CTS. The following parameters were evaluated by surface recording: orthodromic SNCVs in digit-wrist segments for median (index = M2, third = M3 and ring = M4 fingers), ulnar (fourth = U4 finger) and radial (thumb = R1) nerves; SNCVs in palm-wrist segments by surface bipolar stimulation at each metacarpo-phalangeal interspace (second = P2 and third = P3 for the median nerve and fourth = P4 for the ulnar nerve); and distal motor latencies of the median and ulnar nerves. No responses at the wrist were recorded in 22.6% of patients after digital stimulation of M4, whereas the SNCV of P3, the palmar nerve branch arising from digital nerves of the medial side of M3 and the lateral side of M4, was measurable in 93.5% of patients. As significantly expressed (P < 0.001) by the increased ratio of the mean values of P2 and P3 in CTS patients, the SNCV of P3 decreased more frequently and to a greater extent than the SNCV of P2.

Diagnosis of thoracic outlet syndrome. Relative value of electrophysiological studies

The diagnostic utility of various electrophysiological techniques was evaluated in patients with thoracic outlet compression syndrome (TOCS). Our results suggest that in true neurogenic TOCS, there is no standard electrophysiological picture, but that this evolves with the severity of the syndrome. The first changes observed are electromyographic, followed by changes in F-wave and SEPs, followed finally by changes in nerve conduction parameters. EMG study was certainly more informative, showing neurogenic damage not only in limbs with neurological signs but also in about 1/4 of limbs with only subjective symptoms. The study of F-wave and SEPs does not seem to be particularly helpful, however, in view of the peculiar changes found in these patients, SEPs may be a useful complement to EMG. Nerve conduction studies were of little utility since changes in these parameters are only found in patients with long-standing anomalies and severe atrophy.

Literature review of the usefulness of nerve conduction studies and electromyography for the evaluation of patients with carpal tunnel syndrome. AAEM Quality Assurance Committee

The sensitivity and specificity of nerve conduction studies (NCS's) and electromyography (EMG) for the diagnosis of carpal tunnel syndrome (CTS) were evaluated by a critical review of the literature. With a search of the medical literature in English through May 1991, 165 articles were identified and reviewed on the basis of six criteria of scientific methodology. The findings of 11 articles that met all six criteria and the results of 48 additional studies that met four or five criteria are presented. We concluded that median sensory and motor NCS's are valid and reproducible clinical laboratory studies that confirm a clinical diagnosis of CTS with a high degree of sensitivity and specificity. Clinical practice recommendations are made based on a comparison of the sensitivities of the several different median nerve conduction study (NCS) techniques.

Sensitivity of three median-to-ulnar comparative tests in diagnosis of mild carpal tunnel syndrome

We studied 193 hands of 113 patients referred for typical carpal tunnel syndrome (CTS). Ninety-five (49%) hands had normal median distal motor latency (< or = 4.2 ms) and normal or borderline sensory conduction velocity from digit 2 stimulation (> or = 45 m/s). In these cases we performed three median to ulnar comparative tests: (1) difference between median and ulnar distal motor latencies recorded from the second lumbrical and interossei muscles (2L-INT); (2) difference between median and ulnar sensory latencies from digit 4 stimulation (D4M-D4U); and (3) difference between median and ulnar mixed nerve latencies from palmar stimulation (PM-PU). The 2L-INT difference was > or = 0.6 ms in 10% of hands. PM-PU and D4M-D4U were > or = 0.5 ms in 56% and 77% of hands, respectively. The greater sensitivity of D4M-D4U might be explained by the funicular topography and consequent greater susceptibility to compression of the cutaneous fibers from the third interspace which, at the distal carpal tunnel, are clumped superficially in the anteroulnar portion of the median nerve just beneath the transverse ligament.

The prevalence of carpal tunnel syndrome in patients with basal joint arthritis of the thumb

Basal joint arthritis of the thumb and carpal tunnel syndrome are common conditions with an acknowledged coexistence. This article attempts to quantify the prevalence of carpal tunnel syndrome in patients with basal joint arthritis and to examine some of the etiologic factors that affect the coexistence of the two disorders. Of 246 patients who had surgery about the basal joint, 95 patients (39%) were identified by chart review as having carpal tunnel syndrome. Eleven of 122 remaining patients contacted had symptomatic carpal tunnel syndrome confirmed by nerve-conduction studies, bringing the total to 106 (43%). The prevalence was higher in worker's compensation patients and those with diabetes mellitus. The prevalence was lower in men than in women, and patients with inflammatory joint disease were at less risk than those with osteoarthritis. Given this high association, great care should be taken to diagnose or exclude coexistent carpal tunnel syndrome in patients scheduled for basal joint surgery so that, if present, it can be treated at the same time, diminishing the risk of postoperative morbidity and delayed symptoms.

Clinical and electromyographic evidence of carpal tunnel syndrome in a hypertensive patient with chronic beta-blocker treatment

We describe a case of carpal tunnel syndrome (CTS) in a hypertensive man on long term treatment with a beta-blocker, propranolol. The clinical and instrumental findings, including MRI at the wrist, excluded all other possible causes of CTS. The improvement in symptoms and electromyographic findings on discontinuation of the drug suggested that the CTS may have been related to the beta-blocker therapy.