Leprosy, one of the oldest diseases know to humans, still affects almost 10-15 million people troughout the world. Neuropathy affects 15-20% of infected individuals. Therefore leprous neuropathy is still one of the most common neuropathy in the
world.
It is due to infection with Mycobacterium leprae and occurs primarily in Asia and Africa.
The cardinal symptom of leprosy is sensory loss caused by superficial neuropathy. Anesthetic depigmented skin lesions are an important finding and should be sought. Nerve involvement is a hallmark of leprosy. Nerve involvement is rare in other
diseases,
so the finding of skin lesions with enlarged nerves should raise the possibility of leprosy. Nerve involvement tends to occur with skin lesions, and the pattern of nerve involvement parrellels the skin disease. In the tuberculoid from,
mononeuropathy
multiplexis typical pattern, whereas asymmetrical or symmetrical polyneuropathy is most common in the lepromatous form. Motor involvement occurs in a predictable sequence as a result of nerve trunk damage to those nerves that course close to the
skin
surface and hence are locally cool. Nerve involved include the ulnar nerve at the elbow, the deep peroneal branch at the ankle, superficial branches of the facial nerve, and the median nerve at the wrist, and especially the greater auricular
nerve.
Nerve involvement without skin lesions, called pure neural leprosy, can occur. Other characteristic findingg are thickened nerve, trophic ulcers, mutilated digits, and Charcot joint.
In clinically affected nerves, the mother nerve conduction velocities are minimally slow. The terminal latency is often prolonged and the compound muscle action potenials are temporally dispersed and decreased in amplitude. Sensory and mixed
compound
nerve action potentials are often difficult to obtain or else a reduced amplitude. The facial nerve is commonly involved in leprosy. Improvement in motor nerve conduction was reported in leprosy patients under sulfone treatment.
Nerve biopsy reveals subperineurial edema and various amounts of loss of myelinated and unmyelinated fibers. Teased fiber studies reveal paranodal demyelination affection successive internodes. Therefore segmental demyelination is the main
pathology in
leprous neuropathy.
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