1) caused by an infection with Mycobacterium leprae 2) clinical disease occurs in peripheral nervous system, skin, eyes, testes, and upper respiratory tract 3) four different forms occur along a continuum of mild and self-limiting disease to severe and disfiguring disease; they are least to most severe – polar tuberculoid, borderline tuberculoid, borderline lepromatous, and polar lepromatous 4) the lepramatous forms can have an additional superimposed disease exacerbation – lepra type 1 reaction and lepra type 2 reaction 5) lepra states are immunologically mediated inflammatory states 6) an additional disease condition called Lucio’s phenomenon occurs only in Mexico and the Caribbean
Signs and Symptoms
Tuberculoid forms – 1) initial lesion is nonpruritic, hypopigmented, hyperesthesic, and sharply demarcated papule that enlarges peripherally 2) edges elevate as lesion expands, with center becoming atrophic and anesthetic – also with dry, scaly skin and loss of sweat glands and hair follicles Lepromatous forms– 3) skin-colored papules and nodules up to 2 cm in diameter that eventually coalesce 4) leonine facies 5) loss of eyebrows and eyelashes (in lateral areas initially) 8) ulceration of skin over plantar heads 9) foot drop 10) destruction of nasal cartilages with saddle nose deformity 11) blindness (cataracts, uveitis) 12) impotence and infertility 13) amyloidosis
Characteristic Test Findings
Laboratory – 1) false-positive ANA, VDRL, RA Erythema nodosum leprosum – 2) increased alpha-TNF 3) anemia 4) leukocytosis 5) increased transaminases
1) obligate intracellular bacillus with complex cell wall – stains acid fast and best visualized in tissue with modified Fite stain 2) destruction of dermal nerves by T cells (pathognomonic for leprosy) 3) enlargement of peripheral nerves – especially peroneal and ulnar 4) noncaseating granulomas with Langhans’ giant cells and lymphocytes (tuberculoid forms) 5) large clumps of bacilli in dermis (lepromatous forms) 6) foam cells in dermis 7) axonal and Wallerian degeneration
Lucio phenomenon – large, ulcerative lesions on legs that become secondarily infected with bacteria
1) occurs almost entirely in third world countries (India, Brazil, Nigeria, Myanmar, Indonesia, Caribbean) 2) in USA – 200 cases/year; almost entirely in immigrants from those areas, except in Texas where armadillo contact can transmit the organism 3) incubation period is 5-25 years.
1) polar tuberculoid form can be self-limited and heal spontaneously 2) lepra type 1 state – glucocorticoids for 3 months 3) lepra type 2 – antipyretics, steroids for 1-2 weeks, and thalidomide if two courses of steroids has failed 4) rapid surgical decompression of nerve abscesses 5) dapsone is main drug used in combination with rifampin and clofazimine.
Tips for USMLE
1) if question mentions destruction of dermal nerves or neurons by T cells, it is leprosy 2) if question mentions enlarged peripheral nerves, think leprosy 3) if question mentions globi, think leprosy 4) leprosy is chiefly a disease of the dermis
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