Primary cutaneous inoculation with Mycobacterium tuberculosis or bovis in a previously uninfected host will result in a tuberculosis chancre and regional lymphadenopathy. These findings constitute the primary tuberculosis complex of the skin. Skin lesions develop 2 to 4 weeks after inoculation. The condition is most common where the incidence of tuberculosis is high and hygiene is poor. Most patients are children, but young adults can also be infected, particularly those working in the health professions.
The tuberculosis chancre will present as a small papule, scab, or wound that does not heal. A painless ulcer will eventually develop that is quite variable in size, from barely recognizable to as large as 5 cm in diameter. The ulcer is shallow, with a granular or hemorrhagic base, and may be studded with microabscesses, or covered with necrotic debris. The borders are ragged and undermined. As the ulcer ages, the borders become indurated and the ulcer is covered with an adherent crust. Three to 8 weeks following the appearance of the ulcer, a slowly progressive, painless regional lymphadenopathy develops. After several weeks, cold abscesses may perforate the surface of the skin overlying the lymph node to form draining sinuses. More proximal lymph node chains may become involved. In about half of the patients, the course is more acute with fever, pain, and swelling that mimics a typical bacterial infection.
Differential Diagnosis: The primary tuberculosis complex of the skin can be distinguished from cutaneous anthrax in the following manner.
Primary tuberculosis complex of the skin
*Patient is a child or health care worker from highly endemic area
*Lesion may be slowly progressive
* Pustules may be present
* Draining sinuses over regional lymph nodes may be present
* Lesion progression to ulcerative stage is rapid
* Eschar is present
* Ulcer and eschar are surrounded by characteristic non-pitting edema
* Lymphatic vessels are not involved
*Pustules are rare
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