Medical instability in typical and atypical adolescent anorexia nervosa: a systematic review and meta-analysis

This review investigates the relationship between weight and risk of medical instability (specifically bradycardia, hypotension, hypothermia, and hypophosphatemia) in adolescents with typical and atypical anorexia nervosa. Atypical anorexia nervosa, listed as an example under the DSM-5 category of Other Specified Feeding and Eating Disorders (OSFED), describes patients who are not clinically underweight but otherwise meet criteria for anorexia nervosa. There is a lack of empirical evidence exploring medical complications in adolescents presenting with atypical anorexia nervosa. The small number of studies that do exist in this area indicate that medical instability exists across a range of weights, with weight loss being associated with increased medical risk, independent of underweight. The aim of this review was to collate and analyse results from available studies and identify indicators of medical risk in these two groups of adolescents with restrictive eating disorders. Studies were identified by systematic electronic search of medical databases, including PubMed and EMBASE. All studies investigated the relationship between weight and medical instability and included adolescents diagnosed with anorexia nervosa or atypical anorexia nervosa. One randomised controlled trial, five cohort studies and three chart reviews were included, with a total sample size of 2331 participants. Between 29 and 42% of participants presented with medical instability requiring hospitalisation, in the absence of underweight. Underweight adolescents were significantly more likely to have lower blood pressures (p < 0.0001) and bradycardia was significantly associated with greater weight loss (p < 0.05). There were no statistically significant associations found between degree of underweight and heart rate, temperature, or rate of weight loss (p = 0.31, p = 0.46 and p = 0.16, respectively). Adolescents that were less than 70% median body mass index were significantly more likely to have hypophosphatemia (p < 0.05). The findings of this review support the hypothesis that medical instability can occur across a range of weights in adolescent eating disorders, with rapid weight loss being an important indicator of increasing medical risk. Results were limited by the small number of existing studies that contained data for statistical analysis. Rapid weight loss should be considered as an important indicator of medical instability in adolescents presenting with both typical and atypical anorexia nervosa.