What Is Skin Tuberculosis?

Medically reviewed by Casey Gallagher, MD

Skin tuberculosis (TB), also known as cutaneous TB, is an infection most often caused by the Mycobacterium tuberculosis bacteria. It spreads through direct contact via cuts or wounds or when chronic TB spreads from the lungs to the skin; this causes lesions, painful ulcers, severe discolorations, growths, and other symptoms.

A very rare but treatable disease, skin TB represents roughly 1% to 1.5% of all TB cases. This article discusses the causes and symptoms of skin TB and how it’s diagnosed and treated.

Types of Skin Tuberculosis

Skin TB is categorized based on the route of infection. Endogenous skin TB arises when the bacteria spread from the lungs, accessing the skin via the bloodstream or lymphatic system (a system of tubes and nodes that play a critical role in immune function).

Exogenous skin TB occurs from infection outside of the body. In these cases, TB bacteria directly access the skin and bloodstream via a wound, cut, or needle stick. The initial infection is close to the site of exposure.

Latent and Active TB

Of those exposed to TB bacteria, only about 1 in 10 to 20 (5% to 10%) develop active, symptomatic TB. Symptoms typically affect the lungs and include chronic cough, blood or sputum (colored phlegm) when coughing, fever, and chills, among others. Most end up with latent TB, an asymptomatic (without symptoms) and non-contagious form of the condition.

Screening for latent TB is recommended for anyone at greater risk of exposure.

Skin TB Symptoms

Skin TB symptoms vary based on the location and severity of the infection. Rashes, lesions, ulcers, and bumps, known as papules or nodules, arise, typically worsening over time. This leads to a range of specific clinical conditions, commonly occurring two to four weeks after exposure and worsening if untreated. Symptoms include:

• Tuberculous chancre arises first as papules and nodules, which merge to form larger, painless, persistent lesions (patches of discolored, elevated skin). The infection is usually on the face, arms, or legs and can spread to the lymph nodes, causing inflammation (lymphangitis).

• Tuberculous verrucosa cutis typically affects hands, fingers, and toes. It is characterized by plaques and thick red lesions larger than one centimeter (cm) with white or light-colored build-up.

• Scrofuloderma most commonly occurs in people with human immunodeficiency virus (HIV) and TB, as well as infants or children. Scrofuloderma first arises as painless nodules, which grow and burst, forming cold ulcers with larger discolored growths that leak discharges.

• Lupus vulgaris is a skin condition that occurs when TB spreads from the lungs. It is characterized by large, brownish patches of papules (small bumps) that are shiny and tough on the surface (they have the appearance of apple sauce).

• Erythema induratum of Bazin (EIB) affects young and middle-aged women, causing painful, purple lesions to form on the legs. Over time, these recede and turn into scars. If untreated, this issue will reoccur every three to four months.

• Papulonecrotic tuberculids are large lesions on the ears, face, abdomen, or buttocks; infection is accompanied by energy loss, weakness, and fever.

• Tuberculous orificialis is a rare and severe form, most often found in older people. It causes large, painful, irregular ulcers in the mouth, throat, genitals, and anal region. In women, the fallopian tubes and endometrium (the membrane lining the uterus) may also be affected.

• Idiopathic granulomatous mastitis (IGM) occurs in women, causing breast lesions that become painful and scar. This issue is particularly prevalent among breastfeeding people.

Causes

Skin TB, like other forms, is caused by exposure to bacteria. TB typically spreads by inhaling droplets exhaled when a symptomatic person cough, speaks, or sings. It can then spread from the lungs to other parts of the body as bacteria moves through the bloodstream. This is known as endogenous skin TB. You can also become infected endogenously as bacteria access the bloodstream and spread from the lungs throughout the body.

While Mycobacterium tuberculous is at the root of most cases, you can also get skin TB through infection from the Mycobacterium bovis bacterium.

Exogenous skin TB cases arise due to direct contact with the bacteria, usually from a needle stick, cut, or wound. In the latter case,

Given how it’s spread—and since infections are more likely to become problematic in certain cases—some populations are more at-risk of developing skin TB. These include:

• Infants and children under 4

• Older adults over 65

• Alcohol and intravenous (IV) drug users

• Those with weakened immunity due to HIV/AIDS, diabetes, or cancer

• Residents of or immigrants from regions with higher TB rates

• Healthcare workers or others with close contact with infected people

• Those who experience poverty or malnutrition

Diagnosis

When people present with skin TB symptoms, healthcare providers must assess their extent and isolate their exact cause. Alongside assessment of overall health, and medical history, several tests and techniques may be used for diagnosis, including:

• Physical assessment: While visually and physically assessing and feeling (palpating) affected areas won’t confirm cases, it’s a reliable first step in diagnosis.

• Skin biopsy: Biopsy involves harvesting small portions of affected skin for clinical evaluation. Dermatologists collect small samples and send them to an off-site laboratory for evaluation by a pathophysiologist, a healthcare provider specially trained in finding signs of infection.

• TB skin test: A special substance, tuberculin, is injected into the lower part of the arm, causing the area to rise and become thicker. In a second visit, after 48 to 72 hours, the healthcare provider evaluates the size and characteristics of the raised area, which can detect the presence of TB infection. The TB skin test is also known as the PPD or Mantoux test.

• Interferon gamma-release array (IGRA): Blood tests, such as the QuantiFERON-TB Gold Plus (QFT-Plus) and the T-SPOT TB (T-Spot), detect antigens, chemicals released in the blood when fighting off infection. Samples are collected and sent to the clinical laboratory for testing.

• Acid-fast bacillus (AFB) test: Saliva or sputum is collected and clinically evaluated off-site. Using a technique called polymerase chain reaction (PCR), the AFB allows pathophysiologists to find genetic markers of TB bacteria.

Treatment

TB infections of all types are primarily treated with long courses of multi-drug therapy, and specific approaches may vary based on the case. This involves taking combinations of four antibiotics—isoniazid, rifampicin, pyrazinamide, and ethambutol—for six months. Doses are heavier for the first four, followed by a two-month maintenance regimen.

In severe cases of skin TB, surgeries may be attempted to remove problematic growths. In these cases, follow-up cosmetic surgery may be needed to restore the skin’s appearance.

Prognosis

Generally, the outlook is good for people with skin TB who have healthy immune systems. Some forms of this disease resolve on their own, and treatments are highly successful in eradicating the infection. However, the prognosis gets more challenging in those who have conditions that affect immune function or are taking drugs that hinder it. Additionally, some forms of TB infection are resistant to antibiotic therapy, which is factored into care.

Summary

Skin tuberculosis (TB) is a form of TB that affects the skin, causing significant, growths, lesions, ulcers, and other symptoms on different parts of the body. This bacterial infection may arise due to direct exposure to infecting bacteria or as a result of chronic TB. A very rare condition, prolonged courses of antibiotic treatment are highly effective in managing skin TB.

A Word From Verywell

Though uncommon, there’s no denying the impact that a condition like skin TB can have. When it comes to the health of your skin, it’s important to be proactive: to not let things slide. If you suspect something is wrong or are seeing unusual growths on your skin, don’t hesitate to reach out to your healthcare provider for a proper diagnosis.