What is cutaneous tuberculosis
Cutaneous tuberculosis is a rare extrapulmonary form of tuberculosis, although its prevalence is increasing lately, especially in Asia. Despite that, it is quite hard to diagnose skin tuberculosis as the lesions lack specific features and remind of other dermatologic conditions. The term “cutaneous tuberculosis” includes many different manifestations of skin tuberculosis characterized by the development of various lesions on the skin and mucous membranes; still the most common are lupus vulgaris and scrofuloderma, which are described below.
Tuberculosis is an infectious disease caused mainly by Mycobacterium tuberculosis, which primarily affects lungs but may also disseminate throughout the body affecting various organs.
Mycobacteria are typically transmitted from a person who has pulmonary tuberculosis to a healthy one by droplet nuclei which are released into the air when an ill person coughs, sneezes or speaks. In this case, an infected person may develop pulmonary tuberculosis. Another possible route of transmission is the consumption of unboiled bovine milk containing Mycobacteria bovis. In this case, extrapulmonary tuberculosis develops.
In rare cases, the Mycobacteria tuberculosis may be transmitted when the infectious droplet is directly introduced into the skin or mucous membrane upon a recent trauma, cut or breaks in the skin or from surgical procedures performed with unsterilized materials, tattoo or piercing and cause cutaneous tuberculosis.
In some cases, skin tuberculosis may occur due to the BCG vaccination (vaccination with bacillus Calmette-Guerin).
Types of cutaneous tuberculosis and symptoms
- Exogenous cutaneous tuberculosis is caused by the primary inoculation of the bacteria in the skin/mucous membranes.
- Tuberculous chancre
After the inoculation of the bacteria a firm, painless papule or nodule appears. It is reddish-brown and grows slowly. 2-4 weeks later the surface of the lesion ulcerates forming a prone to bleeding granular surface. Regional lymph nodes typically are also affected.
- Verrucous tuberculosis
The lesions appear as solitary painless brownish-red warts, commonly seen in the extremities prone to traumatic injuries – on the knees, elbows, hands, feet and also buttocks.
- Tuberculous chancre
- Endogenous cutaneous tuberculosis occurs secondarily as the result of bacterial dissemination.
- Miliary lesions
Miliary lesions are associated with disseminated tuberculosis. Although in general this form of cutaneous tuberculosis is rare, it may be seen in individuals with comorbid HIV infection.
Military lesions may appear as:
- Multiple small copper-colored spots;
- multiple papules that form pustules while breaking down;
- multiple abscesses (pus-containing lumps) under the skin on the arms and legs, the chest and the buttocks; abscesses near the anus may also occur.
- Miliary lesions
- Orificial tuberculosis
Rarely advanced tuberculosis may cause the development of painful ulcers of the mouth, nose and anal area.
The skin overlying the tissues affected by tuberculosis, typically lymph nodes on the neck, sometimes bones, joints, and testicles, may break down, forming multiple fistulae through which a discharge exudates. The skin can heal spontaneously leaving scars and atrophic lesions.
- Lupus vulgaris
This type of skin tuberculosis is characterized by the presence of the solitary slowly growing nodular reddish-brown plaque with clear margins and crusting surface, usually observed on the head (typically over the bridge of the nose and on the cheeks), neck, lower extremities, and buttocks. Lupus vulgaris may destruct structures such as the nose and ears causing extensive scarring. Lupus vulgaris has a chronic gradual course and is associated with an increased risk of developing squamous cell carcinoma in the scar tissue.
- Tuberculous gumma (also known as a metastatic abscess)
Tuberculous gummas are lesions seen on the trunk and/or extremities, which appear as ulcerating soft dermal/subcutaneous swellings which produce caseous discharge revealing necrotic surface. Gummas occur due to the dissemination of the bacteria from the primary site.
Tuberculids appear as raised rounded masses of the skin bluish-red in color. These lesions occur rarely, usually are observed on the back of the calf.
- Papulonecrotic tuberculid
The lesions known as papulonecrotic tuberculids appear symmetrically on the extremities and the buttocks. The necrotic papules have a crusting surface, if the lesions are removed the deep ulcers are left. Healing of these lesions typically leaves the scars.
- Lichen scrofulosorum
Asymptomatic, colorless or lichenoid, follicular and parafollicular papules which form in clusters on the trunk represent lichen scrofulosorum. This form of tuberculosis in typical for children and adolescents.
Cutaneous tuberculosis responds well to standard antituberculosis treatment which should include at least 4 drugs and last longer than for 6 months.