Pyoderma gangrenosum with large circumferential perianal skin loss in a child.

Pyoderma gangrenosum is an uncommon skin disorder characterised by deep ulcers surrounded by a violaceous over-hanging edge. Although in many instances there is no clear association with any underlying disease, pyoderma gangrenosum has been described in ulcerative colitis, Crohn's disease, polyarthritis, diabetes mellitus and myeloma. Pyoderma gangrenosum may also be seen as a rare manifestation of myeloproliferative disease including leukaemia. In children, as in our case, it may be the presenting feature.