200 Chapter 25
Box 25.1ICD-10 criteria for anorexia nervosa
1 Underweight:<85% of expected weight for age and height (due to weight
loss or, in children, to lack of expected weight gain).
2 Caused by: deliberate dietary restriction, sometimes combined with excessive
exercise, appetite suppressants, or purging (i.e. deliberate vomiting or misuse
of laxatives, enemas, or diuretics).
3 Associated cognitions: intense fear of fatness. Feels fat even when underweight
(or only feels about right when very underweight).
4 Endocrine consequences: Amenorrhoea in post-menarcheal females, unless on
the ‘pill’. (Loss of sexual interest and potency in males. Delayed or arrested
puberty in early-onset cases.)
Note: The ICD-10 Classification of Mental and Behavioural Disorders: Diagnostic
Criteria for Research(World Health Organization, 1993).Epidemiology
Anorexia nervosa has a peak age of onset in the mid-teens and a
female:male ratio of up to 10:1. Onset is uncommon before puberty.
Prevalence estimates for teenage girls mostly range from 0.1% to 0.7%.
Causation
Twin studies have generated contradictory evidence on the role of genetic
predisposition: twins with anorexia are more likely to have affected co-
twins than would be expected by chance, but it is still unclear how far this
is due to shared genes or shared environment. Perfectionism is a common
premorbid trait. Epidemiological studies suggest that social factors can
be important. The contemporary western stereotype of female beauty
involves a degree of slimness that obliges most adolescent girls to diet.
Though most adolescent dieting is benign, social pressures for dieting and
slimness may increase the risk of eating disorders. Liability to eating prob-
lems is particularly high in careers such as modelling and ballet dancing
that particularly emphasise slimness, though it is uncertain whether the
careers themselves makes people develop eating disorders, or whether
having an eating disorder makes these careers more appealing. Anorexia
nervosa is primarily reported in rich countries; in low- and middle-income
countries there is some evidence that anorexia nervosa is commoner in
the most affluent (and thus most westernised) social strata. There is no
specifically ‘anorexogenic’ family background; the disorder is associated
with an increased rate of relatively non-specific problems with family
communication and interaction, and also with a higher rate of weight
problems, physical illness, depression and alcoholism among relatives.
The predisposing role of specific childhood experiences, including sexual
abuse, is uncertain. In many instances, anorexia does seem to have been
precipitated by an adverse life event, though the type of life event does
not appear to be particularly characteristic. The weight gain and change
in body shape due to puberty itself may also contribute to the onset of