Locus minoris resistentiae: An old but still valid way of thinking in medicine.

Locus minoris resistentiae (lmr) refers to a body region more vulnerable than others. This ancient concept, which is also present in Achilles' and Siegfried's old epic myths, weaves through many fields of medicine. In any internal organ or external body region with a congenital or acquired altered defense capacity, a disease process may occur more easily than elsewhere. Illustrative instances are the appearance of hepatocarcinoma on a cirrhotic liver, the onset of lung carcinoma in a tuberculosis scar, cases of osteosarcoma arising in chronic osteomyelitis, and carcinoma complicating chronic cholelithiasis, just to name a few. In dermatology there are countless reports of privileged localization of cutaneous lesions on injured skin which, therefore, represents a typical condition of lmr. The Köbner phenomenon itself features the oldest, simplest, and most common example of lmr, because it denotes the appearance of new lesions pertaining to a previously present skin disorder at the sites of trauma or other insult. The modern transposition of this old but still valid way of thinking in medicine is the reading key of this issue, devoted to lmr in dermatology.