Are we giving azathioprine too late? The case for early immunomodulation in inflammatory bowel disease

Table 1 Vienna classification of Crohn's disease[12]

Parameter
Age at diagnosis	A1 < 40 yr
	A2 ≥ 40 yr
Maximal location of disease prior to first surgery	L1 Terminal ileal
	L2 Colonic
	L3 Ileocolonic
	L4 Any upper GI, regardless of disease elsewhere in bowel
Disease behavior	B1 Nonstricturing, nonpenetrating (inflammatory)
	B2 Stricturing
	B3 Penetrating disease
	Behavior could be defined at any time after diagnosis

Table 2 Montreal classification of Crohn's disease[13]

Parameter
Age at diagnosis	A1 ≤ 16 yr
	A2 17-40 yr
	A3 ≥ 40 yr
Maximal location of disease prior to first surgery	L1 Terminal ileal
	L2 Colonic
	L3 Ileocolonic
	L4 Upper GI only
	+L4 Additional designation to be added if patient has upper GI and distal disease
Disease behavior	B1 Nonstricturing, nonpenetrating (inflammatory)
	B2 Stricturing
	B3 Penetrating disease
	P = Perianal penetrating disease
	Recommended behavior assessed > 5 yr after diagnosis