Leprosy is a chronic, infectious disease caused by Mycobacterium leprae. It mainly affects the peripheral nervous system, skin, and certain other tissues such as the reticulo-endothelial system, bones and joints, mucous membranes, eyes, testes, muscles, and adrenals. Leprosy clinical presentation varies from few to widespread lesions. In most patients, early leprosy presents as macular and hypopigmented lesions. This initial clinical presentation is known as indeterminate leprosy and occurs in individuals who have not developed cell-mediated immunity against M. leprae yet. The number of lesions depends on the genetically determined cellular immunity of the patient. Individuals presenting a vigorous cellular immune response and limited humoral immune responses to M. leprae, usually present few skin lesions. Without treatment, those patients tend to evolve into the polar tuberculoid or borderline tuberculoid form of leprosy. Due to the inability to mount an effective cellular-mediated response to M. leprae and the consequent hematogenous spread of the bacilli, some patients may present with numerous and symmetrically distributed hypochromic lesions. Without treatment these patients evolve to a nonresistant form of leprosy, polar lepromatous.
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