What is Cutaneous Tuberculosis (TB Skin Infection)?
Tuberculosis is an infection usually found in the lungs, caused by a type of bacteria known as Mycobacteria, particularly Mycobacterium tuberculosis. However, when this infection occurs in the skin, it’s referred to as cutaneous tuberculosis, which is quite rare.
The first account of cutaneous tuberculosis was in 1826 by Laennec. He documented a skin lesion, resulting from the bacteria entering his skin. The bacteria causing this was only discovered in 1882 by Robert Koch who identified M. tuberculosis. This bacterium was later isolated from a skin lesion on a person affected by cutaneous tuberculosis.
There are several ways to classify types of cutaneous tuberculosis. The most widely accepted system is based on the following categories:
Exogenous cutaneous tuberculosis includes forms such as tuberculous chancre and tuberculosis verrucosa cutis. Endogenous cutaneous tuberculosis is spread through contact or autoinoculation, including scrofuloderma, orificial tuberculosis and certain cases of lupus vulgaris, or spread through the bloodstream like lupus vulgaris, tuberculous gumma, and acute miliary tuberculosis. There’s also a category known as tuberculids, which includes papulonecrotic tuberculid and lichen scrofulosorum. Cutaneous tuberculosis resulting from a Bacillus Calmette–Guerin (BCG) vaccine also forms another category.
What Causes Cutaneous Tuberculosis (TB Skin Infection)?
Cutaneous tuberculosis, a skin condition, is caused by an infection with M. tuberculosis. This is a contagious disease that can pass from one person with the infection to another. Although less common, Mycobacterium bovis and the BCG vaccine can also lead to this condition.
Risk Factors and Frequency for Cutaneous Tuberculosis (TB Skin Infection)
Cutaneous tuberculosis, a type of tuberculosis that affects the skin, is not as common as pulmonary tuberculosis, which is the kind that affects the lungs. Out of all the people who have tuberculosis symptoms that involve areas other than the lungs, only 1% to 2% actually have cutaneous tuberculosis. This form of tuberculosis is more common in parts of the world where HIV infection is prevalent or where people have weakened immune systems due to other reasons.
Signs and Symptoms of Cutaneous Tuberculosis (TB Skin Infection)
Patients with combined lung and skin tuberculosis might have a range of symptoms. These could include a chronic cough, spitting up phlegm, night sweats, fever, weight loss, coughing up blood, chest pain, and tiredness. Additionally, they could also show symptoms related to the skin. If the tuberculosis is spread throughout the body and has reached the abdomen, symptoms could include abdominal pain and diarrhea. When the tuberculosis affects the brain, it could cause headaches. In some cases, the bacteria could only cause skin-related symptoms.
Sometimes, a patient could have a weakened immune system due to other serious conditions such as AIDS, uncontrolled diabetes, cancer, and end-stage kidney disease. An immune system can also be weakened by excessive use of intravenous drugs or by certain medications that suppress the immune system.
During a physical exam, a doctor might notice different types of skin lesions. These could appear as inflammatory bumps, ulcers, nodules, pus-filled bumps, wart-like plaques, or other types of skin abnormalities.
Testing for Cutaneous Tuberculosis (TB Skin Infection)
When doctors suspect a skin condition called cutaneous tuberculosis, they use a set of methods to confirm it. Firstly, they will take your full medical history and do a physical checkup. This will be followed by a series of tests.
One such test is the Tuberculosis Skin Test, also known as TST or Mantoux test. This procedure involves placing a tiny amount of purified protein derivative (PPD) liquid under your skin, usually on the inside of your wrist or forearm. After about two to three days, they will measure the raised area or bump on your skin where the injection was made.
Another possibility is a blood test called the Serum QuantiFERON-TB Gold (QFT-G) test. This examination helps to spot both active and hidden instances of tuberculosis by checking for the presence of a substance called gamma interferon.
A skin biopsy may also be carried out, which is a highly trusted method for diagnosing cutaneous tuberculosis. Here, a small piece of skin is taken and looked at under a microscope to detect a specific type of bacteria. Further, the skin tissue sample will be grown in a cool environment to see if M. tuberculosis, the bacteria that causes tuberculosis, will develop. This growing process, also known as culture, is considered the most definitive method of diagnosing tuberculosis.
A chest x-ray or a sputum examination might be useful as well. The sputum examination analyses your spit under a microscope and uses a culture method to identify the presence of tuberculosis.
Treatment Options for Cutaneous Tuberculosis (TB Skin Infection)
Treating skin tuberculosis is similar to treating tuberculosis that affects other parts of the body. This treatment typically involves using a combination of drugs. The most common drugs used are isoniazid, rifampicin, pyrazinamide, and either ethambutol or streptomycin. The treatment happens in two stages.
The first stage of treatment, or the intensive phase, is set to quickly reduce the number of M. tuberculosis bacteria in the body. This phase of the treatment usually lasts about two months. After this phase, the patient isn’t contagious anymore, but they still need extra treatment to completely kill the infection. This is where the continuation phase comes in. This phase is also known as the sterilizing phase because its aim is to kill off any remaining bacteria. It lasts for about nine to twelve months.
Treating tuberculosis requires the patient to strictly follow their treatment plan. How well the treatment works can depend on various factors. These can include how strong the patient’s immune system is, their overall health, how advanced the disease is, the type of skin lesions they have, how well they follow their treatment schedule, how long they’re treated, and if they experience any side effects from the medication.
What else can Cutaneous Tuberculosis (TB Skin Infection) be?
When trying to identify skin tuberculosis, doctors have to consider other potential conditions that look similar. This check is called a ‘differential diagnosis.’ Following conditions might be considered:
- Lasting skin infections due to pyoderma vegetans
- A type of fungal infection known as blastomycosis
- Another fungal infection called chromoblastomycosis
- Reactions to medications
- An autoimmune disease named granulomatosis with polyangiitis
- Rosacea causing skin to become granular
- Gumma formation due to syphilis
- Spinulosa keratosis or abnormal growth of skin
- Papular eczema or rash
- Coccidioidomycosis, another fungal infection
- Glossitis, characterized by an inflamed tongue
- Atypical mycobacterial infection, a swimsuit disease
- Chronic granulomatous disease, a rare genetic disorder
- A type of rosacea that looks like lupus
- Another auto-immune disease, nodular vasculitis
- Frostbite-like condition, nodular pernio
Skin tuberculosis can resemble many skin conditions, which can make it quite challenging for doctors to diagnose. Hence, they need to carefully evaluate all possible causes before reaching a conclusion.
What to expect with Cutaneous Tuberculosis (TB Skin Infection)
People who are not immunocompromised, or in other words don’t have a weakened immune system, generally have a good outlook when dealing with cutaneous tuberculosis. On the other hand, even intense treatment might not work for those with a compromised immune system and where the bacteria causing the disease are resistant to multiple drugs.
