Common OSFED presentations

• Atypical anorexia nervosa: all criteria for anorexia nervosa met except that weight is within or above the normal range despite significant weight loss and restrictive behaviours.
• Subthreshold bulimia nervosa: recurrent bingeing and compensatory behaviours occur but at lower frequency/duration than required for full diagnosis.
• Subthreshold binge‑eating disorder: binge episodes present but below diagnostic frequency thresholds or with atypical features.
• Purging disorder: recurrent purging to control weight/shape without objectively large binge episodes.
• Night eating syndrome and other specified patterns: disordered nocturnal eating or other clinically significant patterns not captured by major categories.

Clinical features & risks

• Psychological: severe preoccupation with weight/shape, body image disturbance, mood/anxiety comorbidity, and elevated risk of self‑harm and suicidality.
• Medical: electrolyte disturbance (with purging), dental erosion, GI complications, menstrual dysfunction, and metabolic consequences depending on behaviours and weight history.
• Functional: impairment in social, educational or occupational functioning and reduced quality of life.

Assessment checklist

1. Detailed eating and weight history: dietary restriction, binge/purge behaviours, compensatory methods (vomiting, laxatives, diuretics, excessive exercise), weight trends and weight suppression (difference between highest past weight and current weight).
2. Mental health screen: mood, anxiety, suicidality, substance use, impulsivity and personality factors.
3. Medical evaluation: vitals, orthostatic measures, ECG if purging or bradycardia suspected, labs (electrolytes, renal function, LFTs, TFTs, pregnancy test when relevant), and dental/ENT review for purging consequences.
4. Severity and risk stratification: frequency of behaviours, rapidity of weight loss, medical instability, hydration/electrolyte abnormalities and psychosocial risk.

Treatment principles

• Treat according to dominant presentation (e.g., treat atypical AN like AN in terms of nutritional rehabilitation and monitoring; treat purging disorder with CBT approaches addressing purging behaviours).
• Evidence‑based psychotherapies: enhanced CBT (CBT‑E) is adaptable across OSFED presentations; IPT and DBT‑informed approaches are useful depending on comorbidity and emotion regulation issues.
• Medical and nutritional management: address medical instability, correct electrolyte disturbances, provide supervised re‑feeding when needed and involve dietitians with expertise in eating disorders.
• Pharmacotherapy: SSRIs can reduce binge/purge frequency and treat comorbid mood/anxiety; lisdexamfetamine is not indicated for OSFED per se but may be considered when BED features predominate and local licensing allows. Topiramate may reduce bingeing but has adverse effects—use cautiously.
• Family involvement: family‑based interventions (FBT) often appropriate for adolescents; involve caregivers in monitoring and support where safe and feasible.

Stepped care & referral

• Mild presentations can begin with outpatient CBT‑E or guided self‑help with close monitoring; moderate‑severe cases require specialist multidisciplinary eating‑disorder teams.
• Refer urgently for medical instability (bradycardia, syncope, severe electrolyte disturbance), rapid weight loss, persistent purging with electrolyte abnormalities, or high suicide risk.
• Coordinate care across psychiatry, dietetics, primary care, dentistry and gastroenterology as needed for comprehensive management.

Key takeaways

• OSFED includes diverse, clinically important eating disorder presentations that do not meet full criteria for other specified disorders, yet often carry similar risk and need for treatment.
• Use a formulation‑driven approach: assess medical risk, predominant behaviours and psychological drivers to select CBT‑E, nutritional rehabilitation, pharmacotherapy and family interventions as appropriate.
• Refer to specialist eating‑disorder services for moderate‑severe cases, medical instability or high psychosocial risk; coordinate multidisciplinary care and monitor progress closely.