Induration

Induration (in'doo rā'shən, -dyoo-), a noun, means, in terms of pathology, (a) hardening of an area of the body as a reaction to inflammation, hyperemia, or neoplastic infiltration, or (b) an area or part of the body that has undergone such a reaction. Most often this term is used to describe dermatologic findings.

Examples of usage
"Both erythema and induration appear to be adequate indices of tuberculin sensitivity."

"The erythema had spread to 20 cm, and the central induration had spread to 9 cm."