Skin TB

What is Cutaneous Tuberculosis?
  • Cutaneous TB is the infection of the skin by Mycobacterium tuberculosis
  • It is quite an uncommon form of extra pulmonary TB
  • Cutaneous tuberculosis (CTB) is difficult to diagnose as it resembles many wide ranging differential diagnosis diseases
  • Any part of the body may be infected by Tuberculosis, but mostly it occurs in the lungs (pulmonary tuberculosis)All variants must be recognized to prevent delayed or missed diagnoses
  • Cases of CTB increasing when prevalent with HIV infection & MDR TB
Source of infection of Cutaneous Tuberculosis?
  • Reaches by haematogenous spread
  • Direct extension from latent or active foci of infection
  • Direct into the skin or mucosa of susceptible individual by injury or trauma
  • Increased risk due to following conditions–

    • HIV infection
    • intravenous drug abuse
    • diabetes mellitus
    • immunosuppressive therapy
    • malignancies
    • end-stage renal disease
    • infancy

How to confirm diagnosis?
  • Clinical examination to be done very carefully
  • Skin Biopsy: Histopathological features show – Epitheloid cell nodules embedded in outer shells of the lymphocytes, bacilli rarely seen , presence of Langerhans cells, caseation of granulomas in centre of nodules
  • Mantoux Tuberculin skin test
  • Interferon gamma release assay (IGRA) test
  • Sputum culture –reliable in range of 85% to 98%, but it takes upto a month
  • Detecting source of Extra-pulmonary infection by –

    • X-ray Chest
    • Urine Analysis
    • Blood tests
    • CT scan of chest
    • Bone scans

Epitheloid cell nodules embedded in shells of lymphocytes. Tubercle bacilli are rarely found in the section Langerhans cells are present . Central caesation may be found in the center of the nodules.

Treatment of Bone TB
  • Intensive phase of 2 months of Streptomycin 1 gm + Isoniazid 3oom + Rifampicin 600mg + Pyrazinamide 2gm and Continuation phase of 4 months of Isoniazid 300mg + Rifampin 600mg
  • PAS – (Para-amino salicylic acid) is used alongside Streptomycin or INH.

    • BCG Vaccination protects by blocking the secondary spread, so pathogen limited to primary infection and remains at subclinical levels. The protective effect of BCG in children lasts upto 15 years.

Symptoms of Cutaneous TB?
  • The most common type is Lupus vulgaris (aka ‘Tuberculosis luposa) the symptoms are-

    • Painful cutaneous skin lesions
    • Nodular appearance
    • Usually on face around the nose, ears, eyelids, lips, cheeks and neck
    • Lesions disfigure skin ulcers when not treated
    • Inflammatory papules
    • Verrucous plaques
    • Suppurative nodules
    • Chronic ulcers
    • Other lesions also seen

Differential Diagnosis of Cutaneous TB
Type of Cutaneous TB

Features

TB verrucosa cutis
  • Happens due to direct inoculation via skin
  • Presents as  brown-red wart type growth
  • Lesions on knees, feet, buttocks, elbows & hands
  • Lesions remain for years
  • Clears up without even treatment

 

Scrofuloderma
  • Direct extension from lymph nodes, joints or bone  
  • Often associated with TB of the lungs
  • Lesions are firm & painless
  • Lesions ulcerate on a granular base
  • May heal even without treatment

 

Miliary TB
  • Chronic infection  has spread from  primary infection to other organs via bloodstream
  • Skin lesions are millet-sized, small red spots
  • These develop into abscesses and ulcers
  • More common  HIV, Cancer or AIDS
  • Patient usually  sick
  • Very poor prognosis -many patients die even before they have been diagnosed and treated

 

Tuberculid
  • Generalised exanthema in patients due to immunity of previous infection
  • Patient in good health
  • May have no focus of active TB anywhere
  • Heal with scarring about after 6 weeks

 

Erythema induratum (Bazin disease)
  • Seen as recurring nodules or lumps on back of legs
  • Mostly seen in women
  • These ulcerate and scar
  • Has features of nodular vasculitis

The above differential diagnosis is within Cutaneous TB, but also note the following for overall differential diagnosis

Sarcoidosis

Leprosy

Discoid lupus erythomatosus

Basal cell carcinoma

Deep fungal infection