Tuberculosis Of Skin

INTRODUCTION:
  • 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).
  • Even in countries such as India and China where TB still commonly occurs, cutaneous outbreaks are rare ( Types of cutaneous TB:
Types of cutaneous TB Features
TB verrucosa cutis/ Anatomist's warts/ Prosector's warts/ Verruca necrogenica Occurs after direct inoculation of TB into the skin in someone who has been previously infected with mycobacteria
Begins as a solitary napulonodule following a trivial injury or trauma on one of the extremities that soon acquires a scaly and verrucous surface
Presents as a purplish or brownish-red warty growth
Lesions most often occur on lower limb ,the knees, elbows, hands, feet and buttocks
Lesions may persist for years but can clear up even without treatment
Lupus vulgaris Persistent ,progressive & most common form of cutaneous TB
Caseation is common
Small sharply defined reddish-brown lesions with a gelatinous consistency (called apple-jelly nodules) mostly at root of nose
Plaque shows crusting and induration at the periphery and scarring at the center
Lesions persist for years, leading to disfigurement and sometimes skin cancer
Scrofuloderma Skin lesions result from direct extension of underlying TB infection of lymph nodes, bone or joints
Often associated with TB of the lungs
Firm, painless lesions that eventually ulcerate with a granular base
May heal even without treatment but this takes years and leaves unsightly scars
Miliary TB Post-primary TB infection that has spread from the primary infection (usually in the lungs) to other organs and secondary reactivation tissues via the bloodstream
(Systemic miliary TB occurs when spread is Arterial)
Skin lesions are small (millet-sized) red spots that develop into ulcers and abscesses
More likely in immunocompromised patients, eg HIV, AIDS, cancer
Cryptic type miliary TB usually affects elderly patients
The patient is generally sick
Granulomas are of size 1-2 mm
Choroid tubercles is the pathognomonic finding in miliary TB
Sputum microscopy is usually negative & Montoux test is negative in 20-30%
Tuberculid Generalised exanthem in patients with moderate or high degree of immunity to TB because of previous infection
Usually in good health with no identifiable focus of active TB in skin or elsewhere
Erythema induratum (Bazin disease) presents as recurring nodules or lumps on the back of the legs (mostly women) that may ulcerate and scar. It is a type of nodular vasculitis
Papulonecrotic tuberculid results in crops of recurrent crusted skin papules on knees, elbows, buttocks or lower trunk that heal with scarring after about 6 weeks.
Lichen scrofulosorum is an extending eruption of small follicular papules characterized by involvement of the sweat glands and hair follicles by causing non caseating epitheloid granulomas in young persons with underlying TB.
DIAGNOSIS:

  •  The diagnosis is usually made or confirmed by characteristic histopathological features on skin biopsy.
  • Typical tubercles are caseating epithelioid granulomas that contain acid-fast bacilli. These are detected by tissue staining, culture and polymerase chain reaction (PCR). Other tests that may be necessary include: Tuberculin skin test (Mantoux or PPD test)
  • Interferon gamma release assay blood test

  1. Sputum culture (it may take a month or longer for results to be reported)
  2. Chest X-ray and other radiological tests for extrapulmonary infection.
  3. Interferon gamma release assays (IGRA)
Exam Question
  • Farmer with a single warty lesion on leg may be suggestive of Tuberculosis verrucosa cutis
  • Tuberculides are seen in Lichen scrofulososum
  • Lichen scrofulosorum is an extending eruption of small follicular papules characterized by involvement of the sweat glands and hair follicles by causing non caseating epitheloid granulomas in young persons with underlying TB.
  • Anatomist's warts/ Prosector's warts/ Verruca necrogenica are the synonyms of tuberculosis verrucosa cutis
  • In miliary TB the granulomas are of size 1-2 mm
  • Cryptic type miliary TB usually affects elderly patients
  • Choroid tubercles is the pathognomonic finding in miliary TB
  • The commonest focus of Scrofuloderma is Lymph node
  • Lupus vulgaris is characterized by caseation necrosis
  • Miliary TB & Tuberculosis verrucosa cutis is a form of Post-primary TB infection 
  • Lupus vulgari is the Most common type of cutaneous T.B.
  • Apple Jelly nodule at root of nose is the characteristic finding of Lupus vulgaris
  • Gradually progressive plaque on a buttock with of 15 cm in diameter, annular in shape, with crusting and induration at the periphery and scarring at the center is suggestive of lupus vulgaris
  • Miliary Tuberculosis occur following primary infection and secondary reactivation
  • Sputum microscopy is usually negative & Montoux test is negative in 20-30% in Miliary Tuberculosis
  • Systemic miliary TB occurs when spread occurs via Arterial

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