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Bulimia nervosa matters because the person's weight often looks completely normal, so the diagnosis is easily missed unless the clinician specifically asks about binges and compensatory behaviour. It is diagnosed as recurrent episodes of binge eating, eating a large amount of food with a sense of loss of control, followed by compensatory behaviours such as self-induced vomiting, laxative misuse, fasting, or excessive exercise. For example, imagine a woman of entirely normal weight who secretly eats a whole packet of biscuits then vomits in private, at least weekly for three months. In practice, that hidden binge-purge cycle, not a visibly low weight, is the clue to look for.

Physical signs include Russell's sign, calluses on the knuckles from repeated self-induced vomiting, dental erosion from stomach acid, parotid gland swelling, and hypokalaemia (low blood potassium) from recurrent vomiting or laxative misuse. Unlike anorexia nervosa, bulimia nervosa does not require a significantly low body weight, most patients are within the normal weight range or above it. Picture a patient presenting with unexplained hypokalaemia and dental erosion on routine bloods and dental review: this combination should prompt direct questions about binge-purge behaviour. In practice, checking for Russell's sign and electrolytes can reveal bulimia nervosa that the patient's normal weight would otherwise hide.

• Which drug and dose has the best evidence as an adjunct in bulimia nervosa?
• Which pair of physical findings would most support long-standing self-induced vomiting?
• Why does laxative misuse fail to achieve the weight loss a patient with bulimia nervosa expects?

• Binge eating disorder, no compensatory behaviour after binges, unlike bulimia nervosa's vomiting, laxative misuse, or excessive exercise.
• Anorexia nervosa (binge-purge subtype), requires a significantly low body weight, whereas bulimia nervosa occurs at a normal or above-normal weight.
• Bulimia nervosa, reveals itself through hypokalaemia and Russell's sign, rather than the visibly low weight seen in anorexia nervosa.
• Normal dieting, lacks the recurrent loss-of-control bingeing and compensatory cycle, unlike bulimia nervosa's binge-purge pattern.

• Sertraline does not carry the specific evidence base that fluoxetine has in this disorder.
• Tricyclic antidepressants are not recommended, given their toxicity in overdose.
• Benzodiazepines have no role in treating bulimia nervosa.
• Nail thickening and joint swelling suggest fungal infection or arthritis.
• A goitre with bradycardia suggests hypothyroidism.

• Extract the defining phenomenology, duration, severity and functional-impact clues.
• Match the pattern to the most specific diagnostic or assessment construct.
• Actively test the closest look-alike against the missing or contradictory clue.
• Choose the precise term rather than a broader category that is merely compatible.