With respect to the definitions of IBD, the participants have tried to reach an overall agreement about commonly used terms. Although some of the used definitions are arbitrary, they reflect the every day practice of clinical decision-making.
IG-IBD Statement 1
RESPONSE: ΔCDAI > 100 points or Δ HBI ≥ 3
REMISSION: CDAI < 150 or a HBI < 4, without steroids
RELAPSE: A flare of symptoms with a CDAI > 150 or a HBI > 4 in a patient in clinical remission
RECURRENCE: The appearance of new CD lesions after curative resection of macroscopic disease, usually in the neo-terminal ileum and/or at the anastomotic level, detected by endoscopy, radiology, or surgery
STEROID-REFRACTORY CD: Active disease in spite of an adequate dose and duration of prednisone (0.75–1 mg/kg/day for at least 2 weeks)
STEROID-DEPENDENT CD: inability to stop systemic steroids within 3 months or budesonide within 6–9 months, without clinical relapse or relapse within 3 months after steroid weaning
Clinical disease activity is classified into mild, moderate, and severe according to the CD activity (CDAI) or the Harvey–Bradshaw (HBI) indexes [9], [10]. Mild disease is defined with a CDAI value between 150 and 220 or with a HBI value between 5 and 7. Moderate disease is defined with a CDAI value between 220 and 450 or with a HBI value between 8 and 16. Severe disease is defined with a CDAI value > 450 or with a HBI value > 16 [11]. In clinical practice, however, the evaluation of disease activity is subjected to the overall clinical condition, together with laboratory, endoscopy and imaging findings.
Response is defined by a decrease of CDAI of at least 100 points (ΔCDAI ≥ 100) [6]. In the past years, some studies, including those initially evaluating the effectiveness of infliximab, considered a softer endpoint of response with a reduction in CDAI > 70 points or more from the baseline value and at least a 25% reduction in the total score [12], [13], [14]. It has been recently reported that a decrease in the HBI index ≥ 3 points closely correlates with a ΔCDAI ≥ 100, thus allowing a simpler Crohn's disease activity assessment [15].
Most of the clinical trials, including studies on the efficacy of biologics in CD, have adopted the definition of disease in clinical remission when the CDAI is <150 [11]. It has recently been reported that a HBI index < 4 points closely correlates with a CDAI < 150 points, thus allowing a simpler Crohn's disease activity assessment [15].
A flare-up of symptoms with a CDAI > 150 or a HBI > 4 in a patient with an established CD who is in clinical remission. Other definitions have been proposed for the purposes of clinical trials, but there is a disagreement about this issue [16]. In clinical practice, however, the evaluation of a disease relapse is subjected to the overall clinical condition, laboratory, endoscopy and imaging. Early relapse is defined as a clinical relapse within 3 months after achieving remission with a previous therapy.
The term recurrence is best used to define the reappearance of disease after curative surgical resection. Recurrence is commonly classified as clinical and morphological. Clinical recurrence is defined as the appearance of symptoms after surgical resection, provided that recurrence of lesions is confirmed [17]. Morphological recurrence is defined as the appearance of new lesions after curative surgical resection, even in the absence of overt symptoms, usually located at the neo-terminal ileum and/or anastomosis. The severity of morphological recurrence is commonly graded endoscopically using the Rutgeerts score [18]. Other diagnostic techniques (ultrasound, computed tomography, magnetic resonance imaging) proposed to assess morphological recurrence have not yet been widely accepted.
Steroid-refractory CD is defined as an active disease in spite of an adequate dose and duration of prednisone therapy (0.75–1 mg/kg/day or equivalent for at least 2 weeks).
This definition is slightly different from the ECCO guidelines [16]. There was a complete agreement amongst participants about the duration of steroid therapy, since the timing of biologic therapy is continually changing.
Steroid-dependent CD is defined as (1) the inability to stop systemic steroids within 3 months or budesonide within 6–9 months of starting therapy, without clinical relapse, or as (2) a relapse within 3 months after steroid weaning. Many definitions have been proposed, mainly based on clinical experience and not on physiopathologic evidence [16], [19]. Despite these limitations, an arbitrary definition of steroid dependency is useful as guidance for clinical practice.