Gummas are granulomatous, sometimes ulcerating lesions occurring anywhere on the skin, frequently at sites of trauma. However, they are defined as occurring at non-vital sites, often causing destruction of important structures.
They are commonly found in the skull, tibia, fibula and clavicle, but it is possible for any bone to be involved.
The lesions are necrotic with lymphocyte and polymorph infiltration, healing with scar tissue.
Visceral gummas may also occur, for example in the liver - hepar lobatum - and the testes.
Gummas are seen in tertiary syphilis.