Leprosy

Leprosy, also known as Hansen's disease, is caused by an infection with the bacillus Mycobacterium leprae. It is most common in warm, wet areas in the tropics and subtropics. This chronic infectious disease usually affects the skin, peripheral nerves, and mucous membranes of the aerodigestive tract and eyes. In 2002, the number of new cases detected worldwide was 763,917, with the majority occurring in the endemic areas of Brazil, India, Madagascar, Mozambique, Tanzania, and Nepal. The number of new cases detected in the United States for 2002 was 96 (10). M. leprae is usually spread from person to person in close contact by respiratory droplets. As the bacterium has a propensity to invade peripheral nerves, cranial neuropathies including the facial nerve are not uncommon. Leprosy remains one of the most common causes of peripheral neuropathy worldwide, with some degree of nerve involvement in every case (11). Estimates of 3% to 5% involvement of the facial nerve in leprosy infections have been reported, with facial nerve involvement typically occurring after prolonged infection, on average 12.1 years (12). Both paresis and paralysis can occur, and several investigators have reported that the upper facial nerve branches, particularly the zygomatic branch, are more likely to be affected (13).

Diagnosis is suggested by clinical presentation in endemic areas but can only be confirmed by biopsy. The pathogenesis of nerve damage is from direct injury by the mycobacterium with early invasion of the dermal nerve twigs. As the invasion progresses, Schwann cells and endothelial cells swell from direct infiltration by the organisms. One study demonstrated greater involvement of the distal portions of the nerve, suggesting retrograde spread of infection (11). Treatment of leprosy is with dapsone as well as clofazamine and rifampin. Due to the low likelihood of recovery of nerve function, aggressive surgical rehabilitation and eye protection have been advocated. As the trigeminal nerve is also commonly involved, eye damage from exposure keratitis is a particularly important concern and further advocates for early and aggressive surgical therapy toward eye protection. Facial nerve decompression is not indicated, as involvement of the nerve appears to be along the peripheral portion and not within the enclosed bony segments (11). The mycobacteria are discussed in greater detail in Chapter 12.

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