A-Z OF SKIN

Cutaneous tuberculosis

Cutaneous tuberculosis (CTB) is a skin infection caused by mycobacterium tuberculosis, which mainly causes lung infection, but can involve other organ systems. Most skin TB is the result of spread from internal organs to the skin, but occasionally the bacterium can be directly inoculated into the skin.  Skin manifestations of TB infection are rare, accounting for 1-2 percent of all TB infections, even in the countries where TB is common.

The spectrum of clinical manifestations is wide and depends upon

  • History of previous exposure to the bacteria that causes tuberculosis
  • The immune status of the patient – general health, presence or absence of other infections and whether has developed immunity
  • Whether the infection has developed by direct inoculation or has spread from internal organs or by blood borne spread

The types of cutaneous TB are outlined below.

Types Features
Primary inoculation
tuberculosis
This bacterium infects the individual not previously exposed to TB through a break in the skin that may be an accidental injury or associated with tattooing, piercing, or injections.  In rare cases children, non-immune individuals amidst high TB prevalence regions or poor living conditions can be affected.

  • Painless, small, firm ulcer appears 2-4 weeks after exposure, with a red, tough and hard base, may enlarge to more than 5cm. If left untreated, may last for 12 months or even longer
  • Enlarged lymph nodes, especially in children develop later
  • May affect face, eyes, mouth, hands and legs
  • Sometimes an individual who has previously been exposed to TB and developed a high level of immunity to the bacterium will be re-infected and develop a localized lumpy lesion that may become warty. Biopsy and culture often needed to make the diagnosis
Lupus Vulgaris Spreads to the skin from internal organs where TB occurs and can lead to development of skin lesions. If the individual has developed a fairly high level of immunity to the presence of the bacteria then the skin lesions seen are often localised and well defined.
Scrofuloderma If the patient has lower resistance to the presence of the bacterium and the bacillus directly invades the skin from underlying lymph nodes, bone or joints  the lesion that develops is suppurative like a boil and heals by scarring.
Periorificial
Tuberculosis
Some individuals with poor immune resistance may develop a form of skin infection due to direct spread from the underlying organ tuberculosis  with lesions developing in the larynx, mouth, nose, around the anus and urinary tract. These lesions are often ulcerated, painful and many tuberculosis  organism can be found on biopsy.
Miliary Tuberculosis Individuals with little immune resistance to the infection, malnourished, infections such as HIV or on immune suppressive medications tuberculosis may spread from its primary site of infection to other organs via blood stream and developing single or multiple abscess and lumps  erupt and ulcerate. Prognosis is poor, but recovery after treatment is possible.
Tuberculid Tuberculid is probably best considered as an allergic inflammatory reaction to parts  of  mycobacterium tuberculosis in individuals with a high level of immunity to the bacteria.

The definitive diagnosis is made by tissue (skin biopsy) microscopy, culture and polymerase chain reaction (PCR). Other tests include tuberculin skin test or an interferon gamma release assay blood test.

Aims of treatment:

  • eradication of the bacterium,
  • preventing transmission, screening contacts
  • preventing relapse,
  • preventing the development of drug resistance

Treatment is usally two stages – intensive  treatment over 6-8 weeks followed by  4-7 months of follow up treatment

Active cutaneous TB is treated with anti-tubercular antibiotics (isoniazid, rifampicin, pyrazinamide and ethambutol) or surgical excision if needed. Latent TB may be treated to prevent reactivation of TB infection.

Drug resistant TB is when M. tuberculosis is resistant to at least one of the first-line anti-TB drugs. Multidrug-resistant TB is when M. tuberculosis is resistant to more than one of the anti-TB drugs, which include at least isoniazid and rifampicin. Drug resistance occurs when anti-TB treatment is not adhered to or the individual may be infected with a resistant strain per se. It is an emerging problem in CTB. CTB is best managed in consultation with an Infectious Diseases specialist

Screening of contacts is an essential part of comprehensive management.

Screening for co-infections such as leprosy and HIV is prudent.

 

This information has been written by Mia Yue Yu and Dr Monisha Gupta
Last updated 12/06/18