Electrophysiological Study of Nerves in Type-II Reaction in Leprosy.

BACKGROUND: Leprosy is a chronic granulomatous infection primarily affecting the peripheral nervous system, skin and reticuloendothelial system. Cutaneous nerves are severely affected in lepra reaction and this leads to morbidity.
OBJECTIVE: To study electrophysiological pattern of different nerves involved in Type-II reactions in leprosy.
METHOD: The present study was undertaken in 21 leprosy patients with Type-II reactions attending in and out-patient department of Dermatology & Venereology, B.R.D. Medical College, Gorakhpur from July 2005 to October 2006. This was a prospective case control study in which 20 healthy, age and sex matched people with no evidence of any disease (particularly nerve involvement) were included. LIMITATION: Lesser number of cases were studied. RESULT: The proximal motor conduction latency was significantly prolonged in both ulnar and common peroneal nerve and proximal motor conduction velocity was also significantly reduced. On examining the values beyond 2S.D. of the control value, distal latency was not affected and only proximal conduction was affected in ulnar nerve.
CONCLUSION: In Type II lepra reaction the motor conduction abnormalities are not prominent. Abnormalities are relatively more marked in the proximal segment.

What was known?

Leprosy primarily affects peripheral nervous system. Early change is in nerve conduction velocity.

Introduction

Leprosy is one of the oldest diseases of humankind. The first authentic description of leprosy is given in Sushruta Samhita written in India in 600 B. C. The chronic and placid course of leprosy is punctuated by episodes termed as “reactions.”[1] The clinical diagnosis and treatment of these reactions are of immense importance as these determine the final functional outcome, especially with reference to the nerves.[1234] The determination of status of nerves is, therefore, of great importance in the study of the reactions.

Objective

The objective of this study was to find out electrophysiological pattern of different nerves involved in Type-II reactions in leprosy.

Materials and Methods

The present study was undertaken in 21 leprosy patients with Type-II reactions attending in- and out-patient department of Dermatology and Venereology, B. R. D. Medical College, Gorakhpur from July 2005 to October 2006. Electrophysiological studies were conducted.

Neuro-electrophysiological studies

A detailed neurological examination was carried out to assess the nerve damage. If the nerves were tender and had evidence of nerve damage in the form of motor weakness or sensory loss, then it was taken as clinically affected nerve, and if the nerves were nontender and did not show any motor or sensory dysfunction, it was taken as clinically unaffected nerve. A complete neurological examination would be carried out to assess the nerve damage during ENL. Motor nerve conduction velocities proximal as well as distal of all possible nerves would be measured using Neuro Perfect EMG 2000. Care was taken to ensure that one of the clinically affected and one of the clinically unaffected nerves were included in each case.

Distal conduction studies

The technique of mean corpuscular volume (MCV) was as follows a coaxial needle electrode was inserted in the most distal muscle of the nerve to be examined such as abductor digiti minimi for the ulnar nerve, abductor pollicis brevis for the median nerve, extensor digitorum brevis for the lateral popliteal nerve, and abductor hallucis muscle for posterior tibial nerve. All the nerves were stimulated at two places proximally and distally. The ulnar nerve was stimulated proximally at just above the medial epicondyle posteriorly and distally at wrist along the course of nerve. The median nerve was stimulated proximally at anterior aspect of antecubital fossa and distally at wrist along the course of nerve. The lateral popliteal nerve was stimulated proximally at the neck of fibula and distally at ankle joint anteriorly. The posterior tibial nerve was stimulated proximally posterior to medial malleolus and distally along the course of nerve.

After cleaning the skin, a supramaximal stimulus was applied to ensure activity in all functioning motor nerve fibers and was graded at one per second. It was applied through two electrodes place 18 mm apart along the nerve. The muscle action potential evoked by the stimulation was visually displayed on an oscilloscope, and the distal (DL) and proximal latencies (PL) were measured on the screen. The distance (d) between the stimulation points (proximal stimulation point to distal stimulation point) were measured with a measuring tape. The MCV was calculated using the formula d/DL-PL in m/second for each nerve.

Proximal conduction studies by F-wave

F-wave studies were conducted in each patient in the same nerve, where the distal motor conduction was measured by the method described above. The nerve to be examined was stimulated by surface stimulation electrode dipped in normal saline. The recordings were made by needle electrodes placed at motor points of the relevant muscle. The ground electrode was placed between the stimulating and the recording electrodes. The stimulus frequency was one every second and the pulse was 0.1 ms. Supramaximal shocks were delivered to the nerve at the elbow for the upper limb and at the knee for lower limb respectively by adjusting the voltage to be 20% more than the required to produce a maximal direct motor response. Multiple F-wave at a sweep speed of 5 m. s/dvn and sensitivity of 200 or 100 uv/division were recorded and their latency was measured individually. Latencies were uniformly measured to the beginning of the first deflection from the baseline. Ten F-responses were recorded, and the minimum latency of these (FL) was used to provide information regarding the fastest conducting motor nerve fiber, along the proximal segment. The proximal conduction velocity (FCV) was calculated using the formula FCV = d × 2/(FL-PL); where the “d” is the distance between the proximal site of stimulation and C7 spinous process in upper limb and T12 spinous process in the lower limb.

Twenty healthy, age- and sex-matched persons with no evidence of any disease, involving the peripheral nerves with no history of any prolonged drug therapy were subjected to the motor nerve conduction studies to serve as controls. The values thus obtained were compared using the student's t-test for statistical significance.

Results

Electrophysiological studies were carried out in 21 patients of Type-II reaction in leprosy. Twelve cases (57.15%) had electrophysiological tests within 16–21 days after start of Type-II reaction, 6 cases (28.57%) cases after 21 days, and 3 cases (14.28%) within 8–15 days after onset of Type-II reaction [Table 1]. In comparison to control values, distal latency showed a significant prolongation along the ulnar nerve, common peroneal nerve, and posterior tibial nerve [Table 2] while distal motor conduction velocity showed a significant reduction in ulnar nerve only [Table 3]. The proximal motor conduction latency was significantly prolonged in both ulnar nerve and common peroneal nerve and proximal motor conduction velocity was also significantly reduced in ulnar nerve and common peroneal nerve [Table 4]. On comparing these values, found to be beyond 2S. D. of the control value. It was again observed that a distal latency was not affected [Tables 5 and 6] and only proximal conduction was affected in three ulnar nerves [Tables 7 and 8].

Table 1

Comparative study of the duration between the start of reaction and electrophysiological study of nerve

Table 2

Comparative study of distal latency (m/s) of control and patients

Table 3

Comparative study of distal motor conduction velocity (m/sec) of control and patients

Table 4

Comparative study of proximal motor conduction latency (F-latency in m/s) and proximal motor conduction velocity (F-wave conduction velocity in m/s) of control and patients

Table 5

Number of patients with abnormal (beyond 2 standard deviation of control value) distal motor conduction velocity

Table 6

Number of patients with abnormal (beyond 2 standard deviation of control value) distal latency

Table 7

Number of patients with abnormal (beyond 2 standard deviation of control value) proximal motor conduction velocity (F-wave conduction velocity)

Table 8

Number of patients with abnormal (beyond 2 standard deviation of control value) proximal motor conduction latency (F-latency)

Discussion

The nerves in leprosy are chiefly involved in two zones, the dermal nerves at the periphery and the nerve trunks at certain specific sites. In most of these sites of predilection, the nerve trunks lie superficially over the bony structures.[5] These observations are also reflected in most of the electrophysiological studies on patients with leprosy, where the proximal segments of the nerves are more severely affected than the distal segments.[678] These changes are mainly noted along the clinically affected nerve in comparison to those nerves which are clinically unaffected, although some of the clinically unaffected nerves also reveal abnormal conduction.[69] Reactions in leprosy lead to a generalized disturbance in the nerve functions and thus are of special importance in the final outcome of the disease. The effect of reaction is not only limited to the affected nerves, but it also involves the clinically unaffected nerves.[10111213] The main alteration has been reported to occur in the motor nerve conduction velocities, especially in the affected nerves.[13] The reason ascribed for this decrease in motor conduction velocities has been the inflammatory edema of the granuloma producing ischemia of the nerves associated with Schwann cell dysfunction. Since the ischemia of the nerves mainly involve the larger “a” fibers, the measurement of motor conduction velocity can be taken as an index of involvement of various nerves.[121415]

Most of the electrophysiological studies conducted so far during reactions have been restricted to the distal segments of the nerves, and thus, they exclude the specific sites of predilection of the nerves involvement in leprosy. F waves by virtue of their passage along whole of the nerve segment are extremely useful in detecting abnormalities of motor nerve conduction along the proximal segments. There are studies where F waves are of use in detecting the proximal segment abnormalities in various neuropathies.[16171819] With this background, we have attempted to assess the electrophysiological alterations in the nerve functions of both the proximal as well as distal segment of nerves during Type-II reactions in leprosy.

Conclusion

It is concluded that in Type-II reaction the motor conduction abnormalities are not prominent and the abnormalities are relatively more marked in proximal segment than the distal segment.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

What is new?

Nerve conduction study in Type-II lepra reaction showed little abnormality and quite more in proximal segment than distal segment