ANSWER 30
This picture of loss of menstruation (secondary amenorrhoea), weight loss (to a body mass
index (BMI) of 14.0) and hypokalaemic, hypochloraemic metabolic alkalosis fits well with a
diagnosis of anorexia nervosa. This is a disorder usually of teenagers or young adults char-
acterized by severe weight loss, a disorder of body image (the patient perceiving themself as
being fat despite being objectively thin) and amenorrhoea (or, in men loss of libido or
potency). It is commoner in women than men. Often sufferers from this condition work in a
profession where personal image is very important, e.g. models, actresses, ballet dancers,
and there may be a trigger of an emotional upset such as break-up of a relationship or fail-
ure in important examinations. Patients may abuse purgatives or diuretics or cause self-
induced vomiting. Some patients exhibit the bulimic behaviour of recurrent bouts of
overeating and self-induced vomiting. Patients often deny that they are ill or that they need
medical attention. There is marked wasting with obvious bony prominences. The skin is dry
with growth of lanugo hair over the neck, cheeks and limbs as in this woman. There is usu-
ally a sinus bradycardia and hypotension. Severe physical complications include proximal
myopathy, cardiomyopathy and peripheral neuropathy.
- Hypothalmic/pituitary pathology, e.g. hypopituitarism, hyperprolactinaemia.
- Gonadal failure, e.g. autoimmune ovarian failure, polycystic ovaries.
- Adrenal disease, e.g. Cushing’s disease.
- Thyroid disorders, e.g. both hypothyroidism and hyperthyroidism.
- Severe chronic illnesses, e.g. cancer, chronic renal failure.
! Major causes of secondary amenorrhoea
A number of interrelated mechanisms cause the metabolic alkalosis in this patient. The vom-
iting causes a net loss of hydrogen and chloride ions, causing alkalosis and hypochloraemia.
The loss of fluid by vomiting leads to a contracted plasma volume with consequent second-
ary hyperaldosteronism to conserve sodium and water, but with renal loss of potassium, due
to its secretion in preference to sodium and the fact that fewer hydrogen ions are available
for secretion by the renal tubules. These events combine to give the typical picture of an
alkalosis with low chloride and raised bicarbonate in the blood, and urine which contains
excess potassium and very little chloride. Measurement of 24-h urinary chloride excretion is
helpful. A low urinary chloride excretion (!10 mmol/day) implies vomiting, whereas higher
values suggest diuretic abuse.
This patient should be referred to a unit with a special interest in eating disorders. Other
serious physical illnesses should be excluded with the appropriate investigations. Plasma
levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and oestrogens will
be low. Often such patients are admitted for several weeks in an attempt to make them gain
weight. This involves a high-calorie diet with support from the medical and nursing team.
Supportive psychotherapy tackles the patient’s disordered perception of their body image.
- Anorexia nervosa is a common cause of amenorrhoea in young women.
- Hypokalaemic metabolic alkalosis is the characteristic metabolic abnormality.
- Anorexia nervosa may be associated with abuse of diuretics or purgatives.