Cutaneous tuberculosis (TB) is essentially an invasion of the skin by Mycobacterium tuberculosis, the same bacteria that cause TB of the lungs (pulmonary TB). Cutaneous TB is a relatively uncommon form of extrapulmonary TB (TB infection of other organs and tissues).

Cutaneous tuberculosis (CTb) is highly variable in its clinical presentation, depending on the immunologic status of the patient and the route of inoculation of mycobacteria into the skin. In most cases, the organism reaches the skin via lymphatic or hematogenous spread; inoculation cutaneous tuberculosis does occur.

Causes of Cutaneous Tuberculosis

The clinical lesions occurring in the skin depend on whether the host has had prior infection with M.tuberculosis, and therefore delayed hypersensitivity to the organism, and the inoculation route and mode of spread.

Symptoms of Cutaneous Tuberculosis

• Lesions most often occur on the knees, elbows, hands, feet and buttocks
• Firm, painless lesions that eventually ulcerate with a granular base
• Skin lesions are small (millet-sized) red spots that develop into ulcers and abscesses
• Erythema induratum (Bazin disease) presents as recurring lumps on the back of the legs (mostly women) that may ulcerate and scar.

Diagnosis

Clinical, histologic findings, confirmed by isolation of M.tuberculosis on culture or by PCR.

Treatment

Only PIT and TVC limited to the skin. All other patterns of CT are associated with systemic infection that has disseminated secondarily to the skin. As such, therapy should be aimed at achieving a cure, avoiding relapse, and preventing emergence of drug-resistant mutants.

Antituberculous Therapy Prolonged antituberculous therapy with at least two drugs is indicated for all cases of CT except for TVC that can be excised. Isoniazid and rifampin, supplemented with ethambutol, streptomycin, or pyrazinamide in the initial phases. Isoniazid and rifampin for at least 9 months; can be shortened to 6 months if four drugs are given during the first 2 months.

References

1. https://www.dermnetnz.org/topics/cutaneous-tuberculosis/
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC223933/
3. https://www.sciencedirect.com/science/article/pii/S1472979214205440
4. https://jamanetwork.com/journals/jamadermatology/article-abstract/518106
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4148266/