 Erythema nodosum is due to inflammation of the underlying subcutaneous tissue, and is characterized by septal panniculitis.Another skin lesion, pyoderma gangrenosum, is typically a painful ulcerating nodule.Crohn's disease also increases the risk of blood clots; painful swelling of the lower legs can be a sign of deep venous thrombosis, while difficulty breathing may be a result of pulmonary embolism.