A case of late-onset anorexia nervosa with behavioural dysregulation in a 72-year-old woman, precipitated after olanzapine discontinuation.

This report details the case of a 72-year-old woman with a 5-year history of anorexia nervosa, whose presentation challenges the conventional presentation of anorexia nervosa. She was admitted under the Mental Health Act (MHA) of England and Wales because of escalating behavioural disturbance, including aggression and disinhibition, together with a long-standing pattern of restrictive eating and distorted body image. She presented with a markedly low body mass index, compulsive exercise and profound lack of insight, complicated by dilutional hyponatraemia, a less commonly reported but potentially life-threatening compensatory behaviour. Particularly noteworthy was the close temporal association between olanzapine discontinuation and the recurrence of severe weight loss and behavioural disturbance. Further complicating her assessment was the presence of encopresis and enuresis. Treatment involved multidisciplinary collaboration, thorough investigation to rule out age-related differentials, structured refeeding and cautious medication management, including olanzapine titration. This case highlights the diagnostic and therapeutic challenges of anorexia nervosa in older adults.