Do electrophysiological findings differ according to the clinical severity of carpal tunnel syndrome?

Journal of Neurological Sciences [Turkish] 23:(4)# 9;272-278, 2006 http://www.jns.dergisi.org/text.php3?id=115

Research Article

Do Electrophysiological Findings Differ According To The Clinical Severity of Carpal Tunnel Syndrome?

Alev LEVENTOĞLU¹, Reha KURUOĞLU²

1Kırıkkale University Faculty of Medicine, Department of Neurology, Kırıkkale, Turkey ²Gazi University Faculty of Medicine, Department of Neurology, Ankara, Turkey

Abstract

Aims: To assess the electromyographic (EMG) differences between groups with clinically mild and severe carpal tunnel syndrome (CTS)

Patients and Methods: The charts of 226 CTS patients were retrospectively reviewed and a total of 385 hands that underwent EMG studies were identified. These hands were assigned to mild and severe groups according to the severity of the clinical involvement, as defined by the modified criteria of the Italian CTS study group. Nerve conduction studies in these hands were also classified as mild and severe according to the modified criteria of the same group. Needle EMG findings were also analysed.

Results: A good correlation between the clinical and electrophysiological staging of the CTS was demonstrated (p<0.01). The severity of the neurophysiological involvement showed no significant change between the clinically mild and severely affected groups (p=0.07). However, needle EMG abnormalities (p<0.01) and prolonged median nerve F-wave latencies (p<0.01) were more commonly encountered among the hands showing a severe clinical involvement. Ulnar sensory nerve conduction abnormalities were only observed in the mildly affected group.

Conclusion: These results indicate that the electrophysiological investigation, being a highly sensitive procedure, reflects the pathology, independent of the severity of the clinical involvement.

Keywords: Carpal Tunnel Syndrome, Electromyography

Karpal Tünel Sendromunun Klinik Şiddetiyle Elektrofizyolojik Bulgular Değişiyor mu?

Özet

Amaç: Klinik olarak orta ve şiddetli karpal tünel sendromu (KTS) olan gruplar arasındaki elektrofizyolojik (EMG) farklılıkları değerlendirmek.

Hastalar ve Metod: KTS’si olan 226 hastada retrospektif olarak 385 el EMG çalışmaları ile değerlendirildi. Italyan KTS çalışma grubunun modifiye edilen kriterlerine gore klinik tutulumları orta ve şiddetli olarak ikiye ayrıldı. Sinir iletim çalışmaları da yine aynı grubun modifiye edilmiş kriterlerine gore orta ve şiddetli olarak klasifiye edildi. Iğne EMG bulguları da analiz edildi.

Bulgular: Klinik ve elektrofizyolojik evreleme arasında iyi koralasyon saptandı (p< 0.01). Klinik olarak orta ve şiddetli gruplar arasında nörofizyolojik tutulumun şiddeti arasında önemli fark izlenmedi (p<0.07). Bununla birlikte iğne EMG anormalliği (p<0.01) ve uzamış median F dalga latansı (p<0.01) klinik olarak şiddetli grupta anlamlıydı. Ulnar sinir duyu iletim anormallikleri sadece orta derecede etkilenmiş grupta izlendi.

Sonuçlar: Bu sonuçlar göstermektedir ki elektrofizyolojik değerlendirme patolojiyi yansıtan oldukça duyarlı yöntem olup klinik tutulumun şiddetinden bağımsızdır.

Anahtar Kelimeler: Karpal Tünel Sendromu, Elektromiyografi INTRODUCTION

It has long been a subject of debate whether clinical manifestations of carpal tunnel syndrome (CTS) correlate well with the neurophysiologic findings. Subjective

sensory symptoms are commonplace, but sometimes they are not supported by objective findings in the neurological examination or neurophysiological tests.

Padua et al. proposed a new neurophysiologic classification for CTS

and also demonstrated a nice correlation between the electrophysiologic staging and the severity of clinical symptoms ^(9,11). This group used a clinical scale based on information obtained from patient’s history along with objective neurological findings, which correlated nicely with their proposed neurophysiological classification ⁽¹¹⁾. Later, Bland reported his findings with a slightly modified neurophysiologic scale, which also showed a good correlation with the clinical grading system ⁽¹⁾. Using the clinical grading system developed by Padua et al. ⁽¹¹⁾, we assigned clinical signs into either a mild or a severe group, with a view of assessing the neurophysiologic differences between patients with only subjective complaints and those demonstrating objective neurological findings.

METHODS

We retrospectively reviewed the records of 385 CTS hands, confirmed by a slow sensory nerve conduction velocity of the median nerve, in18 male and 208 female, a total of 226 patients, with a mean age of 49.4± 11.4 (22-78), studied over a 3 year period. There were 202 (52.5%) right and 183 (47.5%) left hand involvement.

Patients with cervical radiculopathies, brachial plexopathies, other entrapment neuropathies of the upper extremity or previous hand surgery, as well as polyneuropathies were left out of the study.

All patients with slow sensory or motor nerve conduction velocities of the median nerve underwent ulnar nerve conduction studies. In case of ulnar nerve conduction abnormalities, the superficial radial nerve sensory conduction, as well as the peroneal and sural nerve conductions was obtained to rule out polyneuropathy. A needle EMG examination was performed on the abductor pollicis brevis muscle in all patients. If spontaneous activity or neurogenic motor unit potentials (MUP) were discovered, abductor digiti minimi and pronator teres muscles were investigated, to rule out C8 radiculopathy and proximal median neuropathies

respectively. Discovery of fibrillation potentials, positive sharp waves or giant MUPs (> 3 mV) in the abductor digiti minimi muscle, prompted a search for other C5-C8 segmental myotomes and cervical paraspinal muscles to look for other evidence of radiculopathy. While the CTS symptoms were present in 350 hands, 35 hands were asymptomatic. Clinical findings in the charts were assigned into mild and severe groups according to the modified criteria of the Italian CTS Study Group (9-11) (Table I). Asymptomatic CTS was graded as stage 0. Therefore the mild group consisted of stage 0-II and the severe group included stage III-V of the previously published criteria (Table I).

Median nerve finger-wrist (digits I-III), palm-wrist segmental orthodromic sensory nerve conduction studies, motor terminal and F-wave latencies, ulnar nerve finger- wrist (digit V) orthodromic sensory nerve conduction studies and motor terminal latency, as well as the needle EMG findings of the abductor pollicis brevis muscle were analyzed from the records of the patients. Sensory latencies were measured to the negative peak of the potential. Surface recording electrodes were used for nerve conduction studies, whereas concentric needle electrodes were utilized for needle EMG. Distance to the active recording electrodes on the thenar and hypothenar eminences were kept at 5 cm for wrist stimulation of the motor nerves. Bandpass filters were set at 20- 20,000 Hz for motor nerve conduction, 20- 2,000 Hz for sensory nerve conduction and 10-10,000 Hz for needle EMG studies. The skin temperature was measured and nerve conduction velocity was corrected to 31º C by means of conversion factors. An additional 1 m/s was added to the sensory and motor nerve conduction velocities of patients older than 60 years of age ⁽⁸⁾. Neurophysiologic data were assessed according to the modified neurophysiologic grading system developed by Padua et al.⁽⁹⁾ (Table II).

Table I. Clinical staging of CTS.

Stage History and Objective Findings 0 Asymptomatic

I Nocturnal paresthesia only Mild

II Nocturnal and diurnal paresthesia III Sensory loss

IV Atrophy and/or weakness of the median innervated thenar muscles Severe

V Paralysis of the median innervated thenar muscles

The lower limits of normal for the median sensory nerve conduction velocity in our laboratory were 32.9 m/s for digit I, 39.4 m/s for digit II, 39.6 m/s for digit III and 35.2 m/s for the palm-wrist segment. Ulnar nerve sensory nerve conduction velocity

for digit V was considered normal if it was above 37.3 m/s. Normality was defined as

<3.8 ms for the median and <3.3 ms for the ulnar nerve motor terminal latencies.

Normal F-wave latency of the median nerve was <32 ms.

Table II. Neurophysiological staging of the CTS according to the median nerve conduction study findings Stage Neurophysiological Findings

0 Negative CTS: Normal findings

I Minimal CTS: Abnormal sensory nerve conduction study of the palm-wrist segment

Mild

II Mild CTS: Abnormal sensory nerve conduction study of any of the finger-wrist (digits I-III) segments

III Moderate CTS: Abnormal sensory nerve conduction study of any of the finger- wrist (digits I-III) segments and prolonged motor terminal latency

IV Severe CTS: Absence of the compound nerve action potential of any finger- wrist segment and prolonged motor terminal latency

Severe

V Extreme CTS: Absence of compound nerve action potential of any finger-wrist segment and compound muscle action potential

Statistical comparison of abnormalities present between the clinically mildly and severely affected groups was made by the chi square analysis. Whenever frequencies fell below 5, Fisher’s exact test was employed. Correlation analysis between

the clinical and neurophysiologic grading systems was performed by the Spearman test. Linear regression analysis between these variables was also carried out. An alpha level of <0.05 was considered significant.

Table III. Neurophysiological findings classified according to the severity of clinical grading (numbers in parentheses indicate percentages)

Clinical Staging Neurophysiological Findings Total

Mild Severe

Mild 166 (43) 192 (50) 358 (93)

Severe 8 (2) 19 (5) 27 (7)

Total 174 (45) 211 (55) 385 (100)

Table IV. Severity of clinical involvement classified according to handedness and sex predilection

Handedness Severity of Clinical Involvement

Mild Severe Total

Right

Male 13 1 14

Female 158 11 169

Left

Male 13 1 14

Female 174 14 188

Total 358 27 385

RESULTS

There were 358 (93%) hands assigned to the mild, and 27 (7%) assigned to the severe group according to the clinical findings. On the other hand, 174 (45%) hands belonged to the mild and 211 (55%) hands to the severe group in terms of neurophysiologic classification. (Table III).

There was a significant correlation between the clinical and neurophysiologic staging as defined by the tables I and II (r=0.30, p<0.01) (Figure). However, the severity of the neurophysiologic impairment showed no significant difference between the clinically mild and severely involved hands (p=0.07). Right or left hand involvement was not related to the severity of the clinical involvement (p=0.68). No relation was observed between the severity of clinical involvement and the gender of the patient (p=1) (Table IV). Female to male ratio was 13/1. Out of 12 abnormally prolonged

median F-wave latencies, 8 (2%) were found in the clinically mild and 4 (15%) were observed in the severely affected group. Absence of F-waves was never observed. Median nerve F-wave abnormalities were more commonly encountered in the clinically severely involved group (p<0.01).

Figure 1: Relationship of clinical to the neurophysiologic grading system of CTS

Although the 7 hands which demonstrated slowing of the ulnar sensory nerve conduction velocity belonged to the clinically mildly involved group, this was not found to be statistically significant (p=1.0). Terminal latency of the ulnar nerve was within normal limits in every hand studied. On the other hand, spontaneous activity in the form of fibrillation potentials and positive sharp waves or giant motor unit potentials on voluntary activation were noted in the needle EMG of the abductor pollicis brevis muscle in 17 (4.5%) of the hands. Two hands each (0.5%) demonstrated spontaneous activity and giant MUPs in the mild group, in contrast to 8 (30%) and 5 (18.5%) hands respectively in the severely affected group. These abnormalities were statistically more frequent in the clinically severe group (p=0.02).

DISCUSSION

We demonstrated a good correlation between the clinical and electrophysiological staging of the CTS, as shown previously by the Italian CTS study group ⁽¹¹⁾ and Bland ⁽¹⁾. However there was no significant difference in the severity of the neurophysiologic involvement between the clinically mild and severely affected hands. This finding most likely reflects the superior sensitivity of the neurophysiologic investigations compared to the clinical assessment and points to the fact that patients with subjective symptoms can demonstrate significant abnormalities in nerve conduction studies. We chose to separate patients into 2 groups according to the presence or absence of objective clinical findings in this retrospective study, instead of utilizing more complex systems as defined in the previous reports ^(1,11), which simplifies the assignment of patients into groups. When this scheme of classification is used, the value of the electrophysiological tests is nicely demonstrated by the obvious neurophysiologic abnormalities in patients

with only subjective symptoms. On the other hand, our findings show that sensory nerve conductions and distal motor latency of the median nerve are not more markedly abnormal in patients with objective clinical signs.

However, it was notable that median F- wave latency prolongations were more commonly encountered in the clinically severely involved hands. Kimura et al.

stated that median F-wave latencies were prolonged in 61 hands of 44 CTS cases, compared to controls ⁽⁶⁾. Menkes et al.

defined the F-wave inversion as the median F-wave latency, which should be shorter than ulnar F-wave latency in healthy subjects, being greater than 1 ms.

In his series of CTS patients, its sensitivity was 76%, which was comparable to the diagnostic yield of digit II-wrist sensory nerve conduction velocity ⁽⁷⁾. We did not utilize this method in the analysis of our findings, as the neurophysiologic grading system of the Italian CTS study group allowed the use of only sensory nerve conduction studies and distal motor latency measurements ⁽⁹⁾

Out of 385 hands investigated, 7 (1.8%) demonstrated slowing of the nerve conduction velocity of the finger-wrist segment of the ulnar nerve. These hands all belonged to the mild group of the clinical classification. Another study demonstrated the presence of 18.4% abnormality in the sensory nerve conduction study of the finger-wrist segment of the ulnar nerve in CTS. However, in contrast to our findings, the authors claim that more than 80 % of the abnormalities were identified among the moderate or severely affected hands.

The severity of involvement in the CTS was defined electrophysiologically ⁽⁴⁾. The finding of a sensory nerve conduction slowing of the ulnar nerve in CTS warrants the inclusion of another sensory nerve conduction study in the upper extremity, such as the superficial radial nerve in order to rule out polyneuropathy. It should be borne in mind that ulnar nerve entrapment at the wrist can coexist with the CTS.

Needle EMG abnormalities were more prevalent in the clinically severe group.

The presence of fibrillation potentials and positive sharp waves is considered indicative of a severe involvement in CTS

(3). The reported prevalence of abnormal needle EMG findings differs between 19- 96%, which is in sharp contrast to the 4.5%

abnormality rate found in this study. This difference most likely stems from the selection of patients and the variety of criteria used in definition of abnormality.

Additionally the other studies employed quantitative measurements of the MUP morphology and included recruitment abnormalities in the assessment of abnormality ^(2,5,7), whereas only the presence of fibrillation potentials and positive sharp waves, as well as the giant MUPs was considered to be indicative of neurogenic involvement in our study. On the other hand Menkes et al. looked for only fibrillation potentials on the needle EMG of the abductor pollicis brevis muscle and found a sensitivity of 19% ⁽⁷⁾. Although we could not demonstrate a significant difference in terms of gender predilection and right or left hand involvement between the clinically mild and severely affected groups, it has previously been reported that men were

more severely affected neurophysiologically ⁽¹²⁾. The same group

has also stated that among patients with a clinical diagnosis of CTS, cases with negative neurophysiologic tests were more often female and left-handed individuals

(9). In conclusion, our findings indicate that compared to the needle EMG of the abductor pollicis brevis muscle, nerve conduction study is a more sensitive tool for the diagnosis of CTS. These results show that the electrophysiological investigation, being a highly sensitive procedure, reflects the pathology, independent of the severity of the clinical involvement and make a significant contribution to the diagnosis.

Correspondence to Alev Leventoğlu

E-mail: alevleventoglu@hotmail.com

Received by: July 19 2006 Revised by: October 12 2006 Accepted : October 17 2006

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