Hypopituitarism and pituitary lesions — formative SAQs

SAQ 1 — The hypoglycaemic newborn (20 marks, ~15 minutes)

A term male newborn is admitted on day four with recurrent hypoglycaemia, prolonged jaundice and poor feeding. On examination he has a small phallus and both testes are undescended. A critical sample taken during a documented blood glucose of 1.8 mmol per litre is pending. Congenital hypopituitarism is suspected. [1]

Questions

1. State the biochemical tests you would ensure were taken on the critical sample and the two hormone deficiencies that together explain the hypoglycaemia. (5 marks) [1]
2. Outline your immediate management before the results return, and state the single most dangerous deficiency to miss. (5 marks) [9]
3. When replacement is started for combined deficiency, state the correct order of glucocorticoid and thyroxine and explain why. (5 marks) [10]
4. List two associated central nervous system findings that would support a congenital cause. (5 marks) [1]

Model answer (must-hit)

1. The critical sample should include paired glucose, cortisol, growth hormone, insulin, free thyroxine and thyroid-stimulating hormone drawn at the time of the hypoglycaemia. The hypoglycaemia is explained by combined growth hormone and cortisol (adrenocorticotrophin) deficiency, both of which are counter-regulatory hormones. [1]
2. Give an intravenous glucose bolus followed by a maintenance infusion, and administer stress-dose intravenous hydrocortisone without waiting for the results. The most dangerous deficiency to miss is central adrenal insufficiency (cortisol deficiency), which can be rapidly fatal. [9]
3. Glucocorticoid must be started before levothyroxine. Thyroxine raises the metabolic rate and accelerates cortisol clearance, so starting it first in a child with unrecognised cortisol deficiency can precipitate an adrenal crisis. [10]
4. Optic nerve hypoplasia and an absent septum pellucidum (septo-optic dysplasia), or a midline cleft lip and palate with a single central incisor, support a congenital midline cause. [1]