Normal median near nerve potential

Nerve damage in leprosy: An electrophysiological evaluation of ulnar and median nerves in patients with clinical neural deficits: A pilot study

Background:

Leprosy involves peripheral nerves sooner or later in the course of the disease leading to gross deformities and disabilities. Sadly, by the time it becomes clinically apparent, the nerve damage is already quite advanced. However, if the preclinical damage is detected early in the course of disease, it can be prevented to a large extent.

Materials and Methods:

We conducted an electrophysiological pilot study on 10 patients with clinically manifest leprosy, in the Dermatology Department of Mahatma Gandhi Institute of Medical Sciences, Sewagram. This study was done to assess the nerve conduction velocity, amplitude and latency of ulnar and median nerves.

Results and Conclusion:

We found reduced conduction velocities besides changes in latency and amplitude in the affected nerves. Changes in sensory nerve conduction were more pronounced. Also, sensory latencies and amplitude changes were more severe than motor latencies and amplitude in those presenting with muscle palsies. However, further studies are going on to identify parameters to detect early nerve damage in leprosy.

Near nerve potencial of sural nerve in leprosy

Leprosy neuropathy is characterized by initial involvement of the small nerve fibers, later followed by involvement of the large fibers, when routine nerve conduction studies become abnormal. To increase the diagnostic yield and precocity of these studies, we applied the near nerve technique to the sural nerve of 8 leprosy patients. Contrary to our expectations, the main component of the sural nerve sensory action potential was abnormal in all patients, but the minimum conduction velocity originating from small 3-6 mm fibers was normal or only mildly involved in three patients. Also, although Schwann cells are the first to be involved in leprosy, the results are suggestive of axonal degeneration instead of demyelination. To better understand the neurophysiology and physiology of leprosy and to increase the accuracy and precocity of the diagnosis, it will be necessary to investigate patients in the very early stages of the disease and to correlate these findings with the corresponding nerve pathology.

Near-nerve potential in lepromatous leprosy

In leprosy, sensory action potentials (SAPs) may be normal in spite of clinical sensory loss. This may result from the early involvement of small nerve fibers, which have potentials that are not detected in routine studies. To evaluate this possibility, we used a near-nerve recording technique that records potentials from nerve fibers as small as 4-6 microm in diameter. We hypothesized that this technique might increase the sensitivity of nerve conduction studies in detecting leprosy neuropathy. We found the technique to be useful for recording conduction abnormalities in recently diagnosed patients, including those with preserved sensation, suggesting that axonal loss may be the underlying mechanism. Contrary to our hypothesis, however, recording the late SAP components did not improve the sensitivity of nerve conduction studies. We suggest that the late components having normal conduction velocities may be generated by either regenerating or remyelinating abnormal fibers, which have an electrophysiological behavior similar to that of normal 4-6-microm-diameter fibers.