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Tuberculoid Leprosy

The characteristic skin lesion shows cellular infiltration extending up to the epidermis and involving the basal layer (Fig. 34.2). The cytoplasm of the cell becomes faintly acidophilic and granular: there are Langhans' giant cells and multiple epithelioid cells surrounded by small lymphocytes. Cutaneous nerves are obliterated by this process but the larger nerves become swollen and destroyed by lepromatous granulomas, which have been known to caseate.

Tuberculoid leprosy is localized to a few sites in the skin and large peripheral nerves. The skin lesions are flat, hypopigmented solitary, well defined, and heal spontaneously from the center. The sebaceous follicles and sweat glands are destroyed within the lesions. The nerves affected are either the cutaneous nerve-twigs associated with the skin lesions or large mixed peripheral nerves. They become greatly thickened by cellular infiltration but the distribution is not symmetrical. Nerve damage is rapid, causing anesthesia and, when motor fibers are involved, weakness and wasting. If there is damage to the autonomic nerve supply there will be localized cyanosis and impaired sweating.

Despite this reaction the bacillus is only rarely detectable in skin smears in tuberculoid leprosy. About half the patients will have bacilli in striated muscle. The lepromin test (see "Laboratory Diagnosis") will be positive.

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Fig. 34.2. A A hypopigmented, sharply defined macular lesion which over 13 years grew to 8 cm x 13 cm. Tuberculoid leprosy may present as small lesions or become very large; they can be single (like this one) or multiple. AFIP 75-15592. B Tuberculoid leprosy. In the dermis there are numerous granulomas composed of epithelioid cells, giant cells, and lymphocytes. Granulomas extend to and invade the epidermis. In the subcutis there are two fascicles of nerves (arrows) virtually destroyed by granulomas. H&E, x6; AFIP 72-12496. C Tuberculoid leprosy. Granulomas composed of epithelioid cells, giant cells, and lymphocytes extendt up to and focally invade the epidermis. There is no subepidermal clear zone. This is from the same section as B. H&E, x200; AFIP 72-12465. (A-C from Meyers 1995).

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