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These are the case findings in their original reveal order, moving from the broader presentation to the most discriminating evidence.
Clue 1
An 82-year-old man is brought to the emergency department by his daughter. She has a key, let herself in this morning as she does most days, and found him already awake but wrong — confused, slow to answer her, unwilling to get out of his armchair. She spoke to him on the telephone the previous evening and he was completely himself, chatty and sharp. He has no diagnosis of dementia and nothing like this has happened before.
Clue 2
The obvious explanation for sudden confusion in an 82-year-old is looked for and not found: no fever, no cough, no urinary symptoms, no new medication, no source of infection anywhere on examination. What the daughter does mention, almost as an aside about the flat rather than about him, is that his boiler failed three days ago and has not been fixed. She says the rooms have been colder than the street. He was sitting in a shirt and cardigan with no blanket, and he had not been drinking.
Clue 3
His observations are slow in every direction at once. Pulse 44 per minute, respiratory rate 8, blood pressure 96/58, saturations 95 per cent on air. His skin is cold and pale — not just at the fingers, which would be unremarkable in a cold flat, but all the way in across the trunk. And he is not shivering. Not a little, not intermittently: not at all.
Clue 4
The tympanic thermometer at triage returned nothing useful — just the word "low" — so a low-reading oesophageal probe is used instead. It gives a core temperature of 29.4 °C. The metabolic panel drawn at the same time is unhelpful in the most informative way possible: glucose 6.8, sodium 138, potassium 4.1, creatinine 112, calcium normal. Nothing on it explains why he is confused.
Diagnosis
Hypothermia
Why the diagnosis fits
The case is built to be mistaken for something else. Sudden confusion in an 82-year-old points almost reflexively at infection, and the correct first move is exactly what happens here — look for a source, and find none. No fever, no cough, no urinary symptoms, no new drug, nothing on the skin. That negative search is not a dead end; it is the finding that forces attention onto the environment, where the answer has been sitting for three days. A failed boiler in winter is enough. Indoor exposure in an older adult with a low resting metabolic rate does not need snow or immersion, and it is easy to overlook precisely because the patient never went anywhere. Two examination findings then do most of the work. The skin is cold across the trunk rather than just at the fingers, which is what separates a genuinely cold core from cold hands in a cold room, and he is not shivering at all. That second one is easy to read backwards. Shivering feels like the expected sign of being cold, so its absence reads as reassurance, when in fact shivering typically ceases once the core temperature reaches 30 to 32 °C — the same range in which paradoxical undressing may be seen. A patient who has stopped shivering is colder than one who is still doing it. The observations agree: pulse 44, respiratory rate 8, everything slowed together. Confirmation needs the right instrument, because a standard tympanic thermometer cannot read this far down and will simply report "low"; a low-reading oesophageal probe returns 29.4 °C, placing him in the moderate band of 28 to 32 °C. The electrocardiogram then supplies the classic corroboration — every interval prolonged, and an elevated J point throwing an extra positive deflection at the QRS–ST junction in the precordial leads. This Osborn wave grows as temperature falls, though it is not unique to hypothermia. The metabolic panel is deliberately unremarkable, and that is its value: it closes hypoglycaemia and the electrolyte causes of delirium in a single order.
Educational reference
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