Endocrine Abstracts

A 24 year old man presented with gait instability, myalgia, and cognitive decline, after a holiday in Crete; his alcohol intake exceeded 200 units/week. He had marked facial dysmorphism, with frontal bossing, and global muscle weakness. He had hypernatraemic dehydration (plasma sodium 175 mmol/l urea 16.9 mmol/l), but denied thirst. Urine concentration was 894 mOsm/kg, excluding diabetes insipidus. CK was elevated at 15,540 U/l. CT brain shown marked hydrocephalus. Rhabdomyolysis secondary to dehydration was diagnosed. He was treated with IV dextrose; when normonatraemic, his conscious level normalised and he experienced normal thirst. A reset osmostat for thirst and AVP release was suspected and he underwent 5% saline infusion. Plasma AVP rose from, 1.4 to 7.3 pmol/l, and linear regression analysis defined a normal osmotic threshold for AVP release, of 283 mOsm/kg (pAVP =0.27 (pOsm-283), r=0.88, P=0.002). Thirst (visual analogue scale) rose appropriately, with a normal osmotic threshold (thirst =0.31 (pOsm – 283), r=0.98, P< 0.0001). The patient therefore had normal osmoregulatory function. However, in the 30 mins following infusion, the patient only drank 400 mls water, despite normal thirst dynamics (normal water intake 700–1200 mls). There was therefore a disconnect between normal osmoregulated thirst and his abnormal drinking behaviour. Sleep studies were normal, but a multiple sleep latency test revealed severe hypersomnolence. The patient remained eunatraemic, with a fixed fluid intake of 2–3 litres daily, until ten years later, when following a flu-like illness, fluid intake fell, there was cognitive decline, and he presented with hypernatraemic dehydration (sodium 166 mmol/l) associated with rhabdomyolysis and a DVT. This is a unique case where intercurrent illness is associated with life threatening hypernatraemia, despite normal osmoregulation. Hydrocephalus has caused cognitive decline and hypersomnolence; without obligate fluid intake the patient is vulnerable to hypernatraemic dehydration.