Nerve damage in non-Iepromatous leprosy and in "reversal" reactions is the result of an immune response to the presence of antigenic material derived from leprosy bacilli within nerves. This immune response damages nerves by in tra-neural epithelioid cell formation, and by compression of Schwann cells due to inflam matory oedema. In lepromatous leprosy the presence of leprosy bacilli induces slow damage to both perineurium and Schwann ceUs. When Erythema Nodosum Le prosum (ENL) develops, associated neuritis is probably brought about by the presence of ENL lesions within the nerves. In the absence of typical skin lesions, the nerve dam age caused by leprosy can llÚmic other conditions. The differential diagnosis in such cases is outlined, and the principies of management of nerve damage due to leprosy are summarised. Some Definitions NERVE INVOLVEMENT This is a general term , meaning anything from the presence of a leprosy bacillus in a nerve to the total destruction of the nerve. NERVE DAMAGE This implies that the presence of bacilli in a nerve or the tissue response to their presence, has caused structural alterations in the nerve. The mere presence of bacilli in a nerve need not be associated with nerve damage. Nerve damage is re cognized more readily histologically than fu nctionally. Nerves that are cJearly abnormal histologically can fu nction without recognisable impairment. For instance, about 30% of the sensory fibres in a nerve must be destroyed before alterations of sensory acuity in the area it subserves can be detected.
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