A 47-year-old man presented with a 2-month history of polyuria and polydipsia. He awoke six times most nights to pass copious volumes of urine despite not drinking any fluid for 4 hours before going to bed.

Investigations:

MR scan of pituitary fossasee image

A water deprivation test confirmed the diagnosis of cranial diabetes insipidus.

What is the most likely underlying diagnosis?

A 55-year-old woman presented with thirst, polyuria and polydipsia. Her symptoms had started 9 months previously following a road traffic accident. Her past medical history was normal and she was not taking any regular medication.

On examination, her blood pressure was 130/80 mmHg with no postural drop. Urine volume measured 5 L in 24 hours.

Investigations:

serum sodium131 mmol/L (137–144)

serum potassium3.6 mmol/L (3.5–4.9)

serum urea2.0 mmol/L (2.5–7.0)

serum corrected calcium2.40 mmol/L (2.20–2.60)

fasting plasma glucose6.4 mmol/L (3.0–6.0)

serum osmolality278 mosmol/kg (278–300)

urinary osmolality100 mosmol/kg (100–1000)

What is the most likely diagnosis?

A 17-year-old Caucasian girl presented with primary amenorrhea.

On examination, her body mass index was 21 kg/m2 (18–25). Her body habitus was normal and she had appropriate breast development. There was no hirsutism or acne.

Investigations:

serum oestradiol<180 pmol/L (200–400)

serum testosterone31.7 nmol/L (0.5–3.0)

serum follicle-stimulating hormone4.0 U/L (2.5–10.0)

serum luteinising hormone6.0 U/L (2.5–10.0)

What is the most likely diagnosis?