Skin TB from an underlying structure is called:

Scrofuloderma: multibacillary type of cutaneous tuberculosis. Earlier known as Tuberculosis cutis colliquativa. It develops as infection into the skin from an underlying focus, usually lymph nodes and occasionally bone, joint. MC in children. MC lymph node involved: Cervical Begins as asymptomatic, bluish red, subcutaneous swellings that persist for several months and overlie an infected gland or joint. Numerous fistulae may intercommunicate beneath ridges of a bluish skin and some may open draining sinuses onto skin surface. Spontaneous healing can occur, but the course is very protracted and leaves typical, cord like scars. Histology shows marked caseating necrosis, in which there are usually numerous bacteria. Antituberculous therapy is usually effective. The differential diagnosis includes Syphilitic gumma, Deep fungal infections, Actinomycosis, and Hidradenitis suppurativa.