Explain the route of infection in cutaneous tuberculosis.

Cutaneous tuberculosis may be acquired by three possible routes. The first route is exogenous infection acquired from an outside source (primary-inoculation tuberculosis and tuberculosis verrucosa cutis). The second route of infection is endogenous spread. This can occur by contiguous spread (scrofuloderma) or by autoinoculation (periorificial tuberculosis) as organisms are passed from internal organ involvement. The final route is through hematogenous or lymphatic dissemination (lupus vulgaris, miliary tuberculosis, and gummas).

Semaan R, Traboulsi R, Kanj S: Primary mycobacterium tuberculosis complex cutaneous infection: report of two cases and literature review, Int J Infect Dis 12(5):472–477, 2008.