Cutaneous tuberculosis is a skin disease caused by infection with mycobacterium tuberculosis, primarily the human type, with rare cases caused by the bovine type.
There are two main pathways of infection: exogenous and endogenous. Exogenous infection occurs through direct contact with minor skin or mucous membrane injuries, while endogenous infection results from the spread of existing tuberculosis lesions in organs or tissues through blood, lymphatic systems, or direct extension to the skin.
According to the WHO’s 2019 data, extrapulmonary tuberculosis (tuberculosis outside the lungs) accounted for 15% of the 7 million new cases in 2018, with cutaneous tuberculosis representing less than 2% of all extrapulmonary cases, approximately 20,000 cases. These numbers only reflect diagnosed cases, leaving potential hidden cases due to misdiagnosis and underdiagnosis(sources from therapeutique-dermatologique.org).
One might question whether misdiagnosis is solely a medical issue. Undeniably, misdiagnosis is influenced by the doctor’s experience, but it is also related to the complexity of the disease’s symptoms.
Symptoms and Classification
Cutaneous tuberculosis can manifest skin lesions anywhere on the body, with specific types of skin tuberculosis having characteristic sites of predilection.
These lesions can take various forms, including nodules, ulcers, wart-like plaques, papules, and necrotic tissue. Without treatment, the disease can persist for several years or even decades.
Based on different modes of transmission, cutaneous tuberculosis can be classified into three categories: exogenous inoculation (primary inoculation tuberculosis, verrucous cutaneous tuberculosis), contiguous spread (scrofuloderma, orificial cutaneous tuberculosis), and hematogenous spread (acute miliary tuberculosis, lupus vulgaris).
Among these, verrucous cutaneous tuberculosis and lupus vulgaris are the most common.
Verrucous Cutaneous Tuberculosis
Verrucous cutaneous tuberculosis accounts for approximately 40% of cutaneous tuberculosis cases and predominantly affects the extremities, such as fingers, backs of hands, and lower legs.
Skin lesions typically present as solitary, painless, firm, wart-like plaques with a diameter of 1-5 cm, exhibiting a violet or reddish-brown color(quotes from therapeutique-dermatologique.org).
Diagnosis and Treatment
Diagnosing cutaneous tuberculosis requires more than just relying on symptoms. A definitive diagnosis involves a combination of skin biopsy and histopathological examination, tuberculin skin testing, bacterial cultures, and other laboratory tests to confirm the presence of cutaneous tuberculosis.
The treatment of cutaneous tuberculosis is similar to that of pulmonary tuberculosis and primarily consists of oral anti-tuberculosis medications, such as isoniazid, rifampin, and pyrazinamide. Skin symptoms typically start to gradually subside with treatment.
For early and smaller cases of cutaneous tuberculosis or lupus vulgaris, surgical excision of the skin lesions is an option.
The best method for preventing cutaneous tuberculosis is through vaccination with the Bacillus Calmette-Guérin (BCG) vaccine. The small scar that many people have on their arms is a sign of BCG vaccination. However, there is a slight chance of infection even after vaccination. It’s important to note that the BCG vaccine is made from a weakened strain of Mycobacterium bovis (bovine tuberculosis), and in rare cases(sources from therapeutique-dermatologique.org), individuals may experience cutaneous side effects, such as local tissue reactions, ulceration, or abscess formation. Some individuals may also develop lupus vulgaris or scrofuloderma as a result of BCG vaccination.