Definitions of relapse Different definitions of relapse were identified (see Table 2). Some definitions were dependent on weight or BMI measures including: BMI < 16.5 for 2 weeks , and BMI < 17.5 [7, 15] or <18.5  for three consecu- tive months. Other definitions included 15% loss of aver- age body weight after achieving normal body weight, either during the index hospitalization or any time dur- ing the 10-year follow-up period . Strober et al.  similarly defined relapse as <85% ideal body weight, which could occur post-discharge or post-recovery. Fur- thermore, relapse could be partial if the individual had recurrence of psychological symptoms but sustained 85% of ideal weight, or full relapse if both psychological symptoms returned and body weight dropped to less than 85%. Several groups [19–22, 24] defined relapse as Morgan-Russell criteria of “poor” (BMI ≤18.5). Other definitions of relapse were dependent on psy-
chiatric symptoms or a combination of psychiatric symptoms and weight changes. Kordy et al.  used a definition of change from DSM-IV partial or full re- mission to full syndrome. Clausen  defined relapse as PSR ≥ 3 or PSR ≤ 2 after 3 months remission. Re- lapse has also been defined as meeting full syndrome criteria (PSR ≥ 5) after 8 weeks of remission [17, 32] and after 12 weeks of remission . Pike’s  more in-depth definition of relapse includes weight loss, EDE increase, medical issues, and a return of disor- dered eating, whereas Martin’s  is the simplest, requiring only that an individual needs psychiatric intervention.
Rates of Relapse Relapse rates of AN were highly variable ranging from a low of 9% to a high of 52% following treatment, with the majority of studies reporting rates greater than 25% [4, 7, 10, 14–18, 21, 22, 24, 28, 29, 32–34]. Studies suggest that adolescents [4, 20, 28] and individuals with restrict- ing subtype AN [7, 29] have a lower likelihood of re- lapse. The first year is the most critical, with particular risk of relapse occurring as early as 3 months post- treatment [4, 7, 15, 32]. Not surprisingly, those who re- cover fully have lower relapse rates (9%) than those who
only partially recover (35%) . Together, these results suggest that while most patients experience brief epi- sodes of recovery, a large proportion relapse. Moreover, the risk is particularly high within the first year.
Follow-Up Variability There was substantial variability in the literature for follow-up procedures. Initial evaluation time points ranged from 4 weeks to 17 months post-treatment [4, 7, 14, 15, 17, 20, 28, 32, 35]. Some studies utilized only a single follow-up time point [15, 28], whereas others followed patients across multiple time points [4, 7, 14, 17, 20, 32, 35]. Some studies had regular follow-up visits (e.g., every 4 weeks , 3 months ), whereas others had irregularly spaced follow-ups (e.g., 2, 6 and 12 year follow up ). Variable follow-up intervals could complicate estima-
tions of relapse rates, since relapse rates can vary by dur- ation of the study follow-up. According to this view, shorter follow-up durations might be associated with lower relapse rates than longer durations. We identified articles supporting this possibility. For example, relapse in a study measuring at 6 months was lower (9% for fully recovered and 35% for partially recovered)  versus studies measuring at 1-year (27–70%) [7, 14] (see Table 3). Relapse rates also varied by remission criteria, with stricter remission criteria displaying lower relapse rates than less stringent criteria. This is evidenced by two 10-year longitudinal studies. Eckert and colleagues  reported higher relapse rates (42%) with less strin- gent relapse criteria and Strober and colleagues  re- ported lower relapse rates (29.5%) with stricter relapse criteria.
Discussion The main finding of this review is that there are almost as many definitions of relapse, remission, and recovery as there are studies of them. To help rectify this state of affairs, we suggest that the eating disorders research and clinical communities evaluate, test, and ultimately adopt standardized definitions for relapse, remission, and re- covery. Depression , bipolar disorder , and schizophrenia  researchers already utilize standard- ized definitions of these constructs. Consensus guide- lines for response, partial response, remission, recovery, and relapse in obsessive compulsive disorder were also recently proposed . However, we could identify no such definitions for AN across organizational websites, including: the Academy for Eating Disorders, Eating Dis- orders Research Society, National Eating Disorders As- sociation, and the European Council on Eating Disorders. Standardizing how relapse and recovery are defined in
research could substantially improve our understanding