ANSWER 71
The likeliest diagnosis is secondary acute hypoaldosteronismdue to failure of the hypo-
thalamic-pituitary-adrenal axis caused by the long-term prednisolone. This is a common
problem in patients on long-term steroids and arises when there is a need for increased
glucocorticoid output, most frequently seen in infections or trauma, including surgery, or
when the patient has prolonged vomiting and therefore cannot take the oral steroid effect-
ively. It presents as here with drowsiness and low blood pressure.
The hyponatraemia is another result of the superimposed illness. It is probably due to a
combination of reduced intake of sodium owing to the anorexia, and dilution of plasma
by the fluid intake. In secondary hypoaldosteronism the renin–angiotensin–aldosterone
system is intact and should operate to retain sodium. This is in contrast to acute primary
hypoaldosternism (Addisonian crisis) when the mineralocorticoid secretion fails as well as
the glucocorticoid secretion, causing hyponatraemia and hyperkalaemia. Acute secondary
hypoaldosteronism is often but erroneously called an Addisonian crisis.
Spread of the infection should also be considered, the prime sites being to the brain, with
either meningitis or cerebral abscess, or locally to cause a pulmonary abscess or empyema.
The patient has a degree of immunosuppression due to her age and the long-term steroid.
The dose of steroid is higher than may appear at first sight as the patient is only 50 kg;
drug doses are usually quoted for a 70 kg male, which in this case would equate to 10 mg
of prednisolone, i.e. an increase of 40 per cent on her dose of 7 mg.
The treatment is immediate empirical intravenous infusion of hydrocortisone and saline.
The patient responded and in 5 h her consciousness level was normal and her blood pres-
sure had risen to 136/78 mmHg. Chest X-ray showed bilateral shadowing consistent with
pneumonia, but no other abnormality.
- Secondary hypoaldosteronism is a medical emergency and requires immediate empir-
ical treatment. - Patients on long-term steroids should have the dose increased when they have intercur-
rent illnesses, and replaced systemically when they have persistent vomiting.