Pyoderma gangrenosum is seen in :

C. i.e. Ulcerative colitis Pyoderma gangrenosum occurs in both ulcerative colitis & Crohn's diseaseQ. But - 50% of PG occurs in association with UC. And - 2% of active UC patients have PG and another 4% UC patients have erythema nodosum. The mean duration of chronic ulcerative colitis before the appearance of erythema nodosum & PG is 5 & 10 years respectively.