lepromatous leprosy

M. leprae is an acid-fast bacillus that cannot be cultured in vitro, grows best at cool temperatures (hence involvement of skin, superficial nerves, nose, testes, and extremities), and has the armadillo as a reservoir in the southern United States. The clinical form is determined by host cell-mediated immunity. Lepromatous disease reflects a failed Th1 response with a Th2 shift: lepromin skin test is negative, bacilli are numerous, and lesions are symmetric, diffuse, and nodular, producing thickened facial skin (leonine facies), loss of eyebrows, nasal septal collapse, testicular destruction with gynaecomastia, and widespread symmetric sensory neuropathy. Tuberculoid leprosy is the opposite pole: a robust Th1 response gives well-formed granulomas, few or no detectable bacilli, a positive lepromin test, and a small number of asymmetric hypopigmented anaesthetic plaques with an enlarged nearby nerve. Treatment of lepromatous disease is dapsone plus rifampin plus clofazimine for at least two years; tuberculoid disease needs dapsone and rifampin for six months. Dapsone causes haemolysis in G6PD deficiency and methaemoglobinaemia.