TB involving skin is estimated to occur in 1%-2% of EPTB cases. This may be from direct infection (cutaneous TB) or immune-mediated reactions to TB infection elsewhere in the body (tuberculids).320 Cutaneous TB typically results from endogenous spread (direct contiguous or lympho-hematogenous) and rarely from exogenous inoculation (TB chancre or verrucosa cutis).321 More common forms of cutaneous TB include scrofuladerma (ulcerative erosions), lupus vulgaris (patches or plaques) and orificialis disease (anal and perianal localizing). Tuberculids are often papulo-nodular in character, ranging from superficial and minimally symptomatic (lichen scrofulosorum) to deeper, painful and, at times, ulcerating panniculitis (erythema induratum of Bazin and papulonecrotic disease).320–322
Diagnosis of cutaneous TB is made by biopsy, with histopathologic assessment and mycobacterial smear and culture. Non-TB mycobacteria and leprosy may also manifest as skin disease, underscoring the diagnostic importance of appropriate tissue-sample testing.
Tuberculid diagnosis can be challenging, often entailing a combination of consistent biopsy histopathology, exclusion of alternate diagnoses, demonstration of TB infection/disease (culture confirmed at another site or supported by chest x-ray, TST and/or IGRA) and response to TB treatment.
We conditionally recommend 6 months of standard anti-TB therapy for treatment of drug-susceptible TB of the skin, including tuberculids (poor evidence).
In addition to more common extra-pulmonary sites previously described, TB may also involve non-nodal glandular tissue (eg, breast), great vessels, endocardium and bone marrow.321,323–326 Although rare, life-threatening immune-mediated responses to M. tuberculosis may also occur more frequently with EPTB. These include, but are not limited to, hemophagocytic lymphohistiocytosis, acute respiratory distress syndrome and severe hypersensitivity reaction to BCG therapy.251,281,327,328
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