Carpal tunnel syndrome - electrodiagnostic aspects of fifty seven symptomatic hands.

JM Murthy, AK Meena 
 Departments of Neurology, Nizam's Institute of Medical Sciences, Panjagutta, Hyderabad, 500082, India., India

Correspondence Address:
J M Murthy
Departments of Neurology, Nizam�SQ�s Institute of Medical Sciences, Panjagutta, Hyderabad, 500082, India.
India

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::   Introduction

Carpal tunnel syndrome (CTS) is the commonest entrapment neuropathy reported from the western countries. In Rochester, Minnesota, the prevalence of CTS was estimated at 125 per 100,000 in 1976-80.[1] Earlier hospital based studies from India reported CTS rarely.[2],[3] In a recent study from South India, CTS accounted for 7% of patients with peripheral nerve disorders and 84% of entrapment neuropathies referred for electrodiagnostic evaluation.[4] The results of electrodiagnostic studies have been found to be highly sensitive and specific.[5],[6],[7],[8],[9],[10] Recently, American Academy of Neurology (AAN), American Academy of Electrodiagnostic Medicine (AAEM), and American Academy of Physical Medicine and Rehabilitation (AAPMR) have defined the standards, guidelines, and options for electrodiagnostic studies of CTS based on a formal literature review and meta-analysis.[11] In this paper we present the electrodiagnostic features in forty one patients using these practice recommendations.

::   Material and method

The subjects of the study include 84 patients who were referred for electrodiagnostic evaluation for acral paraesthesiae. The electrodiagnostic studies included motor and sensory conduction studies by conventional methods. The practice recommendations made by AAN, AAEM and AAPMR were considered while confirming CTS diagnosis by electrodiagnostic studies.[11] The para- meters studied included :



1. Motor Conduction Studi es: a) Motor distal latencies of median and ulnar, b) Amplitude of the negative component of compound action potential (CMAP), c) Median and ulnar conduction velocities

2. Sensory Conduction Studies: a) Sensory onset latencies of median and ulnar nerves by orthodromic stimulation, b) Peak to peak amplitude of sensory nerve action potential (SNAP).

3. Palm-wrist conduction studies : The median and ulnar nerves were stimulated in the palm between 2nd and 3rd and 4th and 5th metacarpal bones respectively at a point, 8 cm distal to the recording electrodes. The onset latencies were measured both for median and ulnar nerves. Median and ulnar nerve palmar latency differences were also calculated.

4. EMG of abductor pollices brevis and first dorsal interossious was done.



The control values were obtained from a previous study of the reference population of 37 healthy individuals. The Figures given in the brackets are mean values plus or minus 2SD accordingly. The criteria for electrodiagnosis of CTS included.[10],[11]



1. Abnormal sensory conduction studies across the wrist of the median nerve in the symptomatic limb (sensory latency > 2SD mean of control, and amplitude <2SD mean of control and/or

2. Abnormal median sensory nerve conduction across the wrist over a short (8cm) conduction distance or abnormal median sensory conduction across the wrist when compared to ulnar nerve conduction (>2SD of control).

3. Abnormal median motor latency in the symptomatic hand (>2SD of control) was also considered, if the patient fulfilled any one of the above two criteria.

::   Results

Of the 84 patients with acral paraesthesiae, electrodiagnostic evidence of CTS was present in 41 patients. 16 patients had evidence on both the sides. All the 41 patients had other signs suggestive of CTS.



1. Median Motor Conduction Studies : Median distal motor latencies were prolonged (control : mean+2SD=4.33 msec) in 67% of symptomatic hands. The amplitudes of CMAPs recorded from the symptomatic hands were abnormal (control: mean-2SD=<3.95 mv) in 33% [Figure 1]. Slowing of median nerve conduction velocity in the forearm segment was observed in 9 (15.8%) patients. The slowing in the motor conduction velocity was associated with prolongation of motor latency in all the patients. None of the patients had any underlying neuropathy or evidence of forearm median-ulnar nerve communication. Needle examination showed evidence of significant spontaneous activity in 40% of the symptomatic hands. Reduced recruitment and/or polyphasic potentials were seen in 47% of these hands.



2. Median Sensory Conduction Studies : Median orthodromic sensory nerve onset latencies were prolonged (control: mean+2SD=>3.2 msec) in 86% of the hands and sensory amplitude was reduced (control: mean-2SD= <5.3 mu) in 82%. The conduction time in the median nerve across the wrist on palmar stimulation was abnormal in 96.5% of the hands. The difference between the median and ulnar nerve latencies across the wrist on palmar stimulation was more than 2SD in 100% of patients [Figure. 1]. These two were the most sensitive electrodiagnostic parameters [Table I].

::   Discussion

Acral paraesthesiae are seen in many disorders including lesions in the cortex. Electrodiagnostic studies confirm the diagnosis of CTS with high degree of sensitivity.[10] The first usefulness of the median motor nerve conduction studies in the diagnosis of CTS was by Simpson in 1956.[12] Gilliatt and Sears[13] later recognised the value of sensory conduction studies. The median nerve conduction abnormalities in CTS are focal and localised to the segment of the median nerve in the carpal tunnel. This has been confirmed by Brown[14] by intraoperative conduction studies. Median sensory nerve conduction across the wrist over a short conduction distance has been shown to be more sensitive than antidromic or orthodromic sensory conduction studies.[5],[9] The difference between the median and ulnar nerve latency measurements with palmar stimulation in patients with CTS is another parameter of diagnostic value.[5],[9],[15] Comparison of the sensitivity evaluation of the several different median nerve conduction studies (NCSs) demonstrated that: (1) median sensory NCSs confirm the clinical diagnosis of CTS more often than the median motor NCSs, (2) the median sensory or mixed nerve conduction from wrist to digit is less sensitive for confirmation of the clinical diagnosis of CTS, compared to techniques which evaluate median sensory or mixed nerve conduction over a short conduction distance across the carpal tunnel, or techniques which compare sensory or mixed nerve conduction of the median nerve through the carpal tunnel to sensory or mixed nerve conduction of the ulnar nerve or radial nerve in the same hand.[10] The five studies, which met all the six literature classification criteria, reported sensitivities of electrodiagnostic studies ranging from 49% to 84%.[11] In this study the incidence of electrodiagnostic abnormalities was greater when compared to average Figures published.[10] The median nerve sensory conduction over a short distance across the carpal tunnel was abnormal in 96.5% patients and the median and ulnar latency difference with palmar stimulation was 100%. Such findings suggest that the patient population was biased and included patients with advanced CTS.[16],[17],[18],[19] It is likely that patients with severe disease were referred for electrodiagnostic evaluation. Motor conduction studies were abnormal in upto 67% of patients which also supports such supposition. Jackson and Clifford[9] showed that the incidence of electrodiagnostic abnormalities increased according to the severity of the median compression.

References