Cutaneous Tuberculosis

CTB: Introduction & Classification - Skin's Silent Siege

Cutaneous Tuberculosis (CTB): Chronic, specific skin infection by Mycobacterium tuberculosis complex (MTBC). Incidence varies with systemic TB prevalence.

Routes of Infection:

• Exogenous: Direct inoculation into skin/mucosa (e.g., trauma, abrasion).
• Endogenous: From an internal TB focus via:
  • Haematogenous spread
  • Lymphatic extension
  • Contiguous spread (e.g., from infected lymph node or bone).

Classification (Simplified):

⭐ Lupus vulgaris, the most common CTB form, classically shows "apple-jelly" nodules (yellowish-brown lupus follicles) on diascopy.

CTB Forms (1): Lupus Vulgaris & Scrofuloderma - Lesions Unmasked

• Lupus Vulgaris (LV)
  • Most common CTB in India; chronic, progressive, paucibacillary. Often on face.
  • Source: Hematogenous, lymphatic, direct extension.
  • Lesions: Reddish-brown, soft plaques/nodules; active border, central atrophic scarring.
    • Diascopy: "Apple-jelly" nodules (yellowish-brown). (📌 AJELLY: Apple JElly LupY).
  • Sites: Face (nose, cheeks, earlobes), neck, extremities.
  • Complications: Disfigurement, contractures, ↑ risk SCC (Marjolin's ulcer) in chronic lesions.
  • 
• Scrofuloderma (SD)
  • Subcutaneous TB; from underlying focus (lymph node, bone, joint).
  • Lesions: Firm, painless nodules → soften, adhere to skin → ulcers & discharging sinuses.
    • Overlying skin: Bluish-red/violaceous.
  • Features: "Cord-like" tracts, keloidal/puckered scars.
  • Sites: Neck (cervical lymphadenitis - common), axilla, groin.

⭐ "Apple-jelly" nodules on diascopy are a hallmark of Lupus Vulgaris.

CTB Forms (2): TBVC, Gumma & Tuberculids - Diverse Disguises

• Tuberculosis Verrucosa Cutis (TBVC)
  • Warty, hyperkeratotic plaques ("butcher's/prosector's wart").
  • Sites: Hands, buttocks, knees (trauma).
  • Patho: Exogenous reinfection in sensitized (high immunity).
  • AFB: Scanty. Histo: Pseudoepitheliomatous hyperplasia.
• Tuberculous Gumma (Metastatic Abscess)
  • Subcutaneous nodules → cold abscess → ulcers, sinuses.
  • Patho: Hematogenous spread from internal focus.
  • Often in immunocompromised. AFB: May be positive.
• Tuberculids (Hypersensitivity Reactions)
  • Symmetrical eruptions; immune reaction to M. tb antigens.
  • AFB: Absent in lesions. Tuberculin test: Strongly positive. Respond to ATT.
  • Types:
    • Papulonecrotic Tuberculid (PNT): Crusted papules → varioliform scars. Extensors.
    • Lichen Scrofulosorum: Minute, grouped, lichenoid papules. Trunk. Asymptomatic.
    • Erythema Induratum of Bazin (EIB): Tender nodules, posterior calves; may ulcerate. Nodular vasculitis.

    ⭐ EIB is strongly associated with an underlying tuberculous focus, often occult; requires ATT.

CTB: Diagnosis & Management - Cracking & Conquering

• Diagnosis:
  • Mantoux test: Usually positive (PPD).
  • Skin Biopsy: Cornerstone for confirmation.
    • HPE: Tuberculoid granulomas; caseation varies.
    • AFB stain (ZN): Often negative (paucibacillary forms).
    • Culture (LJ): Gold standard, low sensitivity.
    • TB-PCR: Rapid, aids early diagnosis.

• Management:
  • Multi-drug Anti-Tubercular Therapy (ATT).
  • Regimen (New Cases): 2 months (HRZE) + 4 months (HR).
    • H: Isoniazid 5 mg/kg
    • R: Rifampicin 10 mg/kg
    • Z: Pyrazinamide 25 mg/kg
    • E: Ethambutol 15 mg/kg
  • Surgery: Adjunctive for specific lesions (e.g., non-healing ulcers, sinuses).

⭐ Rifampicin is pivotal in ATT, offering potent bactericidal and sterilizing effects against M. tuberculosis.

High‑Yield Points - ⚡ Biggest Takeaways

• Lupus vulgaris is the most common form of cutaneous TB, presenting with apple-jelly nodules on diascopy.
• Scrofuloderma arises from direct extension of underlying tuberculous foci, commonly lymph nodes or bones.
• Tuberculosis verrucosa cutis (TBVC) is a warty plaque from exogenous inoculation in previously sensitized individuals.
• Erythema induratum of Bazin is a nodular vasculitis or lobular panniculitis, often on the posterior calves.
• Diagnosis involves biopsy for granulomas, AFB staining, and PCR for M. tuberculosis.
• Standard Anti-Tuberculous Therapy (ATT) is the mainstay of treatment for all forms.
• BCG-osis can occur post-vaccination in immunocompromised individuals, presenting as a localized or disseminated infection.