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Leprosy is a chronic, systemic infection characterized by progressive cutaneous lesions. It's sometimes called Hansen's disease. Ninety percent of leprosy cases in the United States are found in immigrants from leprosy-endemic regions (Mexico, India, and Southeast Asia). Incubation time is frequently 3 to 5 years but has been reported 6 months to several decades. It's commonly transmitted by humans, but a few cases have been transmitted from animals (armadillos and primates).

With timely and correct treatment, this seldom fatal disease has a good prognosis. Acute episodes may intensify leprosy's slowly progressing course, but whether such exacerbations are part of the disease process or a reaction to therapy remains unclear.

Untreated, leprosy can cause severe disability, blindness, and deformities. Leprosy takes three distinct forms:

  • Lepromatous leprosy, the most serious form, causes damage to the upper respiratory tract, eyes, testes, nerves, and skin.
  • Tuberculoid leprosy affects peripheral nerves and sometimes the surrounding skin, especially on the face, arms, legs, and buttocks.
  • Borderline (dimorphous) leprosy has characteristics of both lepromatous and tuberculoid leprosy. In this form of leprosy, skin lesions appear diffuse and poorly defined.


Leprosy is caused by Mycobacterium leprae, an acid­fast bacillus that attacks cutaneous tissue and peripheral nerves, especially the ulnar, radial, posteropopliteal, anterotibial, and facial nerves. The central nervous system appears highly resistant.

Susceptibility is highest during childhood and seems to decrease with age. Presumably, transmission occurs through airborne respiratory droplets that contain M. leprae or by inoculation through skin breaks (from a contaminated hypodermic or tattoo needle, for example).

Signs and symptoms

Once infected with the mycobacteria, the average incubation period is two to three years, but it can range from 6 months to 40 years or longer. In 90% of patients the first sign of the disease is a feeling of numbness, which may precede skin lesions by a number of years. Temperature is the first sensation lost, followed by light touch, pain and then deep pressure. Sensory loss usually begins in the extremities (toes and fingertips).

The first skin lesion is usually the indeterminate type, which causes one or a few hypopigmented (pale) spots before evolving into the borderline, tuberculoid or lepromatous types.

Diagnostic tests

Identification of acid-fast bacilli in skin and nasal mucosa scrapings confirms a diagnosis of leprosy. A skin biopsy shows the typical histologic pattern of nerve changes. The skin biopsy and scrapings also are evaluated to determine the percentage of fully intact cells (morphologic index) and to measure the amount of bacteria present (bacterial index).


Leprosy usually responds to antimicrobial therapy with sulfones, primarily oral dapsone, which may cause hypersensitivity reactions. Especially dangerous but rare - reactions include hepatitis and exfoliative dermatitis. If these reactions occur, sulfone therapy should stop at once.

If leprosy fails to respond to sulfones or if the patient has respiratory or other complications, an alternative therapy, such as rifampin or clofazimine, may be effective.

Plantar ulcers are prevented by having the patient wear rigid-soled footwear or walking plaster casts. Contractures of the hand may be prevented by physical therapy. Reconstructive surgery is some­times helpful. Nerve and tendon transplants and release of contractures also increase function. Plastic surgery for facial deformities may be needed. Ophthalmologic examinations should be done for all patients because 48% have evidence of sight­threatening ocular complications.


Prevention consists of avoiding close physical contact with untreated people. People on long-term medication become noninfectious (they do not transmit the organism that causes the disease).

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