Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the typical acid-base disturbance seen in Cushing's syndrome?

1. Respiratory acidosis

2. Hypokalemic metabolic alkalosis

3. Metabolic acidosis

4. Respiratory alkalosis

The correct answer is: Hypokalemic metabolic alkalosis

In Cushing's syndrome, one of the hallmark features is an excess of corticosteroids, particularly cortisol. This condition often leads to an array of metabolic disturbances, one of which is hypokalemic metabolic alkalosis. Hypokalemic metabolic alkalosis occurs due to the effects of excess cortisol on renal function. Cortisol can stimulate the renal tubules to excrete potassium while reabsorbing sodium. The loss of potassium leads to hypokalemia, while the retention of sodium can also promote the retention of bicarbonate, resulting in metabolic alkalosis. The combination of low potassium levels and increased bicarbonate leads to the alkalotic state. Additionally, the excess glucocorticoids in Cushing's syndrome can also have an anti-inflammatory effect, affecting the acid-base balance indirectly, but the primary disturbance remains the hypokalemic metabolic alkalosis, making it the typical acid-base disturbance associated with this syndrome.