Comorbid mental disorders during long-term course in a nationwide cohort of patients with anorexia nervosa

Objective: Comorbid mental disorders in anorexia nervosa during long-term course require detailed studies. Method: This matched cohort study was based on nationwide Danish register data of all patients born 1961–2008 with a first-time ICD-10 diagnosis of anorexia nervosa (AN) between 1994 and 2018 at age 8–32 and matched controls taken from all individuals without an eating disorder (ED). For nine categories of non-eating mental disorders, time from date of first AN-diagnosis (inclusion date) to time of first diagnosis, accounting for censoring, was studied by use of time-stratified Cox models. Results: A total of 9,985 patients with AN (93.5% females) and 49,351 matched controls were followed for a median (IQR) of 9.0 (4.4–15.7) years. For patients, there was about 25% and 55% risk of receiving any non-ED disorder during the first 2 years and two decades after inclusion, respectively. A hazard ratio (HR) of seven for any non-ED was found for the first 12 months after inclusion, a ratio that reduced to two at five or more years after inclusion. During the first years, large HRs ranging in 6–9 were found for affective, autism spectrum, personality, and obsessive–compulsive disorders with the latter displaying the highest continuous increased risk. The HR at 12 months after inclusion was highest for any non-ED disorder and affective disorders in patients aged 8–13 at diagnosis. Discussion: Comorbid mental disorders in AN are most frequently diagnosed in the first years after diagnosis of AN and on longer terms imply a double immediate risk.