Diabetes insipidus and polyuria-polydipsia — OSCE

Station brief (candidate)

• Explain the diagnosis in plain language: the surgery to remove the tumour was very close to the gland that makes a water-control hormone (vasopressin), and that gland is no longer making enough, so his body cannot hold on to water — he passes a lot of dilute urine and gets very thirsty. This is called central diabetes insipidus. ^[1]
• Reassure the parents that it is treatable: a medicine called desmopressin replaces the missing hormone, tells the kidneys to hold water, and brings the urine volume and thirst back to normal. ^[4]
• Explain the key safety rule simply: the medicine is powerful, so we let the urine "break through" a little before each dose. If he is kept holding water all the time and keeps drinking, the salt in his blood can drop too low and make him unwell — so we do not over-treat, and we watch the blood tests. ^[4]
• Warn gently about the early post-surgery pattern: in the first couple of weeks the water balance can swing — a phase of too much urine, then a phase of holding too much water, then settling. This is why the blood sodium is checked often and the dose is adjusted, not fixed. ^[4]
• Explain the broader plan: the same surgery can affect the other pituitary hormones (steroid, thyroid, growth), so he will be checked for those and given replacements if needed. Coordinated endocrine and neurosurgical follow-up will be arranged. ^[1]
• Give concrete safety-netting: keep water available, watch for signs of too much or too little water (drowsiness, headache, or on the other hand very high urine output and intense thirst), have a sick-day plan, and contact the team early if he is vomiting or not drinking. ^[11]