Primary inoculation TB

Results from introduction of mycobactria to an individual who was not previously infected with TB or was immunized with the m.bovis.

After entry they multiply in tissue macrophages and spread to regional lymph node. An inflammatory papule develops in 2-4 wks at the inoculation sites that breaks down into a firm, non healing shallow, nontender. Undermined ulcer with a granulomatous base. Painless lymphadenopathy is evident 3-8 wks.

Numerous bacilli are present at the inoculation site and regional lymph node. This ulceroglandular complex is the skin analog of the Ghon complex.

As with all Tb infection the clinical course depends upon the host immune response . Tuberculin sensitivity usually is coincident with the development of lymphadenopaty. Epitheloid granulomas are evident in the skin and lymph node. 

The primary lesion heals with scaring after 1-3 month. With a less effective host immune response, bacterial load remains high and healing is delayed for up to 12 month. regional nodes may suppurate,erode and perforate the surface of the overlying skin(scrofuloderma).latent foci of infection can remain at the site and progress to lupus vulgaris or TB verrucosa cutis.