Functional Impairment of Skin Appendages Due to Peripheral Nerve Involvement by Mycobacterium leprae.

In the earliest stage of Mycobacterium leprae infection, bacteria parasitize fine fiber twigs of autonomic peripheral nerves supplying efferent impulses to appendages of the skin. This obligate intracellular pathogen invades Schwann cells, the glial cells of peripheral nerves. Intracellular events inhibit Schwann cell physiology in complex ways, which include demyelination and dedifferentiation. Ultimately, axons embraced by their surrounding dysfunctional glia are damaged by poorly understood mechanisms. Loss of nerve conduction impairs the functions of skin appendages including hair growth, sebaceous gland secretion, sweating, and skin pigmentation. At the clinical level, these changes may be subtle and may precede the more obvious anesthetic skin lesions associated with Hansen's disease. Recognizing the early signs of skin appendage malfunction may aid in diagnosis leading to initiation of antimycobacterial treatment. Effective therapy administered early during infection may prevent irreversible peripheral nerve destruction, the presage for morbid complications of leprosy.