A worrying decline
She had been independent the previous week. Now she was sleepy, intermittently confused and walking poorly. There was no focal weakness and no clear fever.
The medication clue
Her medicines had recently been changed for hypertension. A thiazide-type diuretic had been added, and she had also been drinking excessive plain water because relatives thought dehydration caused the weakness.
The twist
Serum sodium was markedly low. The presentation was acute symptomatic hyponatraemia—not dementia.
Take-home message
Acute cognitive change should trigger a search for reversible metabolic, infectious, drug-related and neurological causes. Always review recently added medicines.
Diagnostic principle: do not let the first plausible label stop the search when an important detail does not fit.
Educational note: This is a teaching composite, not a substitute for patient-specific diagnosis or treatment. Real patients require direct clinical assessment and appropriate investigations.