Papulonecrotic tuberculid

A 48-year-old woman presented to an outpatient clinic in Chengdu, China, with a 6-year history of recurring lesions on her trunk and extremities. The lesions began as 2- to 10-mm purplish-red papules and pustules, which developed necrosis and crusting, and then resolved spontaneously within 4 weeks, leaving atrophic varioliform scars (Figure 1). The lesions recurred irregularly with no pruritus or pain. She denied weight loss, chronic cough or fever. We performed a skin biopsy of a lesion, which showed lymphocytic vasculitis associated with fibrinoid necrosis and thrombotic occlusion of individual vessels (Appendix 1, supplemental figure, available at www.cmaj.ca/lookup/doi/10.1503/cmaj.231460/tab-related-content). To exclude infectious dermatoses, acid-fast staining and meta-genomic next-generation sequencing of lesional samples were completed and results were negative. Given the local estimated incidence of tuberculosis (52 per 100 000), we performed a chest computed tomography, which showed multifocal calcified nodules in both lungs, suggesting a history of pulmonary tuberculosis. An interferon-γ release assay of Mycobacterium tuberculosis was positive, confirming latent tuberculosis infection. We diagnosed papulonecrotic tuberculid and started a 6-month regimen that included 2 months of isoniazid, rifampicin, pyrazinamide and ethambutol and 4 months of isoniazid and rifampicin. The patient had no new lesions within 2 months and recovered fully after 6 months.

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Figure 1:

(A) Multiple purplish-red papulonodular or papulopustular lesions with necrosis and crusting on the extremities of a 48-year-old woman, which resolved into (B) atrophic varioliform scars.

Cutaneous tuberculosis can occur as both true tuberculosis and tuberculids. Tuberculids are hypersensitivity reactions to mycobacterial antigens with little intralesional mycobacteria.1 A tuberculid is an immunological response to degenerated M. tuberculosis or their antigenic fragments from occult or inapparent tuberculosis elsewhere in the body.2 Papulonecrotic tuberculid is an uncommon type of tuberculid, and predominantly affects young, immunocompetent people.1^,2 Histopathology is crucial for diagnosis and typically shows vasculitis, vascular occlusion with fibrinoid necrosis, and wedge-shaped necrosis of the superficial dermis without tuberculoid granulomas.2^,3 Even when papulonecrotic tuberculid is suspected, diagnosis can be challenging since acid-fast staining of lesions is usually negative and polymerase chain reaction testing for M. tuberculosis has a low positivity rate.2 Other helpful diagnostic clues include evidence of current or past tuberculosis infection, a strongly positive result on a tuberculin skin test and a positive result on an interferon-γ release assay of M. tuberculosis. Papulonecrotic tuberculid generally responds well to standard antituberculosis treatment.2^,3