What is tuberculosis?

Tuberculosis is a systemic infectious disease that can affect any organ system, including the skin. Only approximately 5% to 10% of infections lead to clinical disease. The lungs, however, are the most commonly involved organ. Cutaneous tuberculosis has a broad clinical spectrum depending on the route of infection, virulence of the organism, and immune status of the host (Table 30-2). Lupus vulgaris and scrofuloderma, although rare, are the two most common forms of cutaneous tuberculosis.

Table 30-2. Classification of Cutaneous Tuberculosis
	CLASSIFICATION		PRIMARY INFECTION (NONIMMUNE HOST)		SECONDARY INFECTION (IMMUNE HOST)
	Exogenous
	Primary inoculation tuberculosis		×
	Tuberculosis verrucosa cutis				×
	Endogenous
	Scrofuloderma				×
	Periorificial tuberculosis				×
	Hematogenous/lymphatic
	Lupus vulgaris				×
	Acute miliary tuberculosis		×
	Gummas		×
	Data from 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.