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Classification of lepra
Last reviewed: 06.07.2025
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According to the classification adopted at the VI International Congress on Leprosy in Madrid in 1953, the following forms of leprosy are distinguished: lepromatous, tuberculoid, undifferentiated and borderline (dimorphic). The first two types of leprosy are recognized as polar.
The lepromatous type is the most severe form of the disease, highly contagious, and difficult to treat. The skin, mucous membranes, lymph nodes, visceral organs, eyes, and peripheral nerves are affected. A typical skin lesion is a diffuse and limited infiltrate (lepromatous infiltration and leproma). Bacteriological examination of scrapings from skin lesions and the nasal mucosa reveals a huge amount of the pathogen. The intradermal lepromin test is negative. Histological examination of the lesions reveals a lepromatous granuloma, the main cellular elements of which are Virchow's leprosy cells - macrophages with "foamy" cytoplasm containing leprosy mycobacteria.
The tuberculoid type of leprosy is characterized by a milder course of the disease, and better treatment results. The skin, peripheral nerves, and lymph nodes are affected. A typical skin lesion is a tuberculoid rash. Mycobacterium leprosy is not detected in scrapings from skin lesions and the nasal mucosa. The lepromin test is positive. Histological examination of the lesions reveals a granuloma consisting mainly of epithelioid cells surrounded by lymphoid cells. Giant Langhans cells are found in the center of the granuloma.
Undifferentiated leprosy is a relatively benign form of the disease characterized by damage to the skin and peripheral nerves. Skin damage is expressed in the appearance of flat erythematous spots. Bacteriological examination of scrapings from skin lesions and the nasal mucosa usually does not reveal the pathogen. The reaction to lepromin can be negative or positive depending on the trend of the infectious process (one or another polar type of leprosy). Histologically, lymphocytic infiltration of the lesions is noted.
Borderline (dimorphic) leprosy is a malignant form of the disease characterized by lesions of the skin, mucous membranes, and peripheral nerves. Clinical signs of skin lesions are characteristic of both the lepromatous and tuberculoid types of leprosy. Bacteriological examination of scrapings from skin lesions reveals large numbers of leprosy mycobacteria, but not always in scrapings from the nasal mucosa. The lepromin test is usually negative. Histological examination of the lesions reveals a granuloma consisting of cellular elements characteristic of both polar types of leprosy.
D. Ridley and W. Jopling (1962, 1966) proposed a classification of leprosy that included five main groups (tuberculoid type, lepromatous type, borderline tuberculoid group, borderline leprosy, borderline lepromatous group) and two additional groups (subpolar lepromatosis and undifferentiated leprosy). The 10th International Congress on Leprosy (Bergen, 1973) and the WHO Expert Committee on Leprosy (WHO, 1982) recommend using this classification. At the same time, in the opinion of the WHO Expert Committee on Leprosy, the Madrid Classification of Leprosy (WHO, 1982) should also be widely used.
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