2.2.11 Leprosy

Hansen's disease.

Mainly a tropical disease. Malnutrition, poverty are major risk factors. Worldwide around 200 000 new cases are registered every year (predominantly in India, Brazil, Indonesia, Nepal, Congo, Mozambique, Philippines).

Chronic, minimally contagious infection with Mycobacterium leprae, developing after an incubation period of 3 to 20 years, mainly affecting the skin and peripheral nerves.

Leprosy is caused by Mycobacterium leprae, an intracellular gram-positive acid-fast bacillus.

• Skin involvement: solitary or multiple hypopigmented, anhidrotic and hypoesthetic macules or plaques, nodules (leproma), red macules with peripheral papular spread, solitary or multiple hypopigmented areas with reduced sensation. A leonine face may be seen. 
• Neurological features: palpable thickening of nerves (e.g. ulnar), impaired sensation, motor and sensory problems (muscle atrophy), trophic ulcers. 
• Eye involvement includes: lagophthalmia, uveitis, cataract, corneal involvement, optic neuropathy, diffuse involvement (panophthalmia leprosa), which can lead to loss of vision and blindness.

Hypopigmented macules with sensitivity loss can occur anywhere on the body. Leproma nodules are frequently located on the face, ears or hands.

Leprosy can be classified by clinical manifestations, which span from indeterminate leprosy (IL, potential initial stage), tuberculoid leprosy (TT), lepromatous leprosy (LL) and borderline leprosy (spectrum of transient forms, BT, BL, BB). This disease also can be classified by the number of bacilli; paucibacillary leprosy (corresponding to tuberculoid leprosy) and multibacillary leprosy (corresponding to lepromatous leprosy).

Immune reactions associated with the presence of M. leprae are known as leprosy reactions: 

Type 1: type IV immunologic reaction; flare-up of old skin lesions and neuritis. Occurs during therapy.

Type 2: type III immunologic reaction in lepromatous or borderline leprosy. Skin changes known as erythema nodosum leprosum.

A polymerase chain reaction in skin can be used to identify Mycobacterium leprae but can be negative in tuberculoid forms without ruling out the diagnosis.

Tuberculoid leprosy manifests as granuloma with epithelioid histiocytes surrounding small cutaneous nerves, giant cells may be seen. Bacilli are usually scarce but can be found by immunohistochemistry.

In lepromatous leprosy, macrophages (Virchow cells) can be found in poorly circumscribed nodules in the dermis, numerous bacilli are present especially in cutaneous nerves and in the vessels. Bacilli can be visualized by Ziehl-Neelsen and immunohistochemistry staining. 

The course can change in any direction between lepromatous, tuberculoid and borderline forms.

Neurological deficiencies, amputation, mutilations, chronic ulcers, blindness.

The diagnosis is suspected when clinically evocative skin lesions +/- palpable nerves or neurological defects are observed. The diagnosis is confirmed by the existence of a specific leproid granuloma histologically, and/or by the identification of M. leprae (by Ziehl-Neelsen or Fite, and immunohistochemistry staining and/or PCR) especially in lepromatous form.

Hypopigmented lesions: eczema, psoriasis, dermatophytes infection, seborrheic dermatitis, mycosis fungoides, vitiligo, pityriasis versicolor, pityriasis rosea.

Nodules: sarcoidosis, cutaneous lymphoma, leishmaniasis, syphilis. 

The treatment is a combination of antibiotics (rifampicin, dapsone and clofazimine) and the duration of the treatment depends on the form of disease. Paucibacillary leprosy is treated for 6 months. Multibacillary leprosy is treated for at least 12 months.