Papulonecrotic Tuberculid

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Papulonecrotic Tuberculid

Papulonecrotic tuberculid (PNT) is a rare hypersensitivity reaction to Mycobacterium tuberculosis. It is not an active infection of the skin itself, but rather an immunologic response to systemic tuberculosis.

Key Clinical Features

  • Lesions: Symmetrical, firm, dusky-red papules that develop central necrosis and crusting.
  • Distribution: Predominantly affects extensor surfaces (knees, elbows, buttocks).
  • Course: Lesions heal with “varioliform” (pox-like) scarring.

Diagnostic & Management Pearls

Feature Details
Immunology High PPD (tuberculin skin test) positivity; high cell-mediated immunity to TB.
Diagnosis Clinical, biopsy (shows necrotizing vasculitis/granulomas), and evidence of TB focus elsewhere.
High-Yield Exam Pearl:

  • Treatment: The skin lesions resolve rapidly with anti-tuberculous therapy.
  • Differential: Must differentiate from other necrotizing papular conditions like Pityriasis Lichenoides et Varioliformis Acuta (PLEVA) or vasculitis. The presence of underlying TB is the definitive diagnostic link for PNT.