Tuberculosis of the Skin
Tuberculosis of the skin is caused by the same organism that causes tuberculosis elsewhere in the body, i.e., mycobacterium tuberculosis. Mycobacterium bovis and, very rarely, the Bacillus Calmette-Guerin (BCG) vaccine may give rise to the condition. The skin can get infected primarily or following an infection in some other part of the body. Primary skin tuberculosis is can be of two types: a localized tuberculous chancre that starts of as a nodule and then ulcerates and a generalized form that is characterized by the formation of eruptions, both with or without pus, all over the body.
Secondary skin tuberculosis develops many years after a primary infection. The intensity of the manifestation depends upon the person’s immunological status, producing lupus vulgaris in individuals with fairly good immunity, tuberculosis verrucosa cutis or scrofuloderma in those with moderate immunity, and tuberculosis orificialis in people with low immunity.
Lupus vulgaris is known to affect the face, upper extremities, buttocks, thighs, and legs. It starts off as a soft, reddish, and raised lesion, which gradually spreads irregularly, usually with one progressive end and the opposite healing end. These lesions can form ulcers that form thick crusts and then destroy the tissue in the area, leading to scar formation and deformities.
Pathologists, anatomists, veterinary doctors, and butchers are known to develop tuberculosis verrucosa cutis as an occupational hazard because these people often have to handle tuberculous tissue. These lesions arise from deep within the skin and are warty in appearance. Scrofuloderma usually develops in the skin overlying a tubercular lymph node. However, it can occur in the skin over a joint or bone infected with tuberculosis. In this type of skin tuberculosis, sinuses form in the area and drain out pus.
Tuberculosis cutis orificialis develops in individuals already suffering from tuberculosis of some internal organ, when they re-infect themselves in areas where the mucus membranes meet the skin. Thus, the lips and mouth may get involved when a person coughs and spits out the infected sputum as a result of the disease in the lungs. Similarly, intestinal tuberculosis patients may develop lesions in the region surrounding the anus as this region comes in contact with feces loaded with tubercle bacilli. People suffering from genito-urinary tuberculosis may develop lesions around their genitals.
Tuberculides are usually an external manifestation of internal tuberculosis in individuals with good immunity. Such patients normally do not manifest any symptoms of the internal disease and these skin lesions are probably caused due to spread of the bacilli through the blood. Papulonecrotic tuberculides are a variation of the above form where multiple eruptions develop mostly on the limbs and heal by scar formation, which resembles that of small pox. Lichen scrofulosorum are eruptions of skin tuberculosis that resemble lichen planus, a type of skin allergy. The lesions have a typical purplish hue and tend to form crusts.
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