Functional and Cognitive Decline in an Older Adult With Severe Hyponatremia and Undiagnosed Hypothyroidism: A Geriatric Perspective.

Hyponatremia is the most common electrolyte disturbance in older adults and often presents with nonspecific symptoms such as confusion, gait instability, and functional decline, frequently mistaken for ageing. Hypothyroidism is another reversible condition in the elderly that can impair free-water clearance and contribute to chronic slowing and cognitive dysfunction. We report an octogenarian man with chronic obstructive pulmonary disease, hypertension, and recently diagnosed diabetes who presented with one week of fluctuating altered mental status and hallucinations, superimposed on six months of progressive weakness and near-complete loss of independence. Evaluation revealed severe euvolemic hyponatremia (110 mEq/L), low serum osmolality, elevated urine sodium and osmolality, and marked hypothyroidism, with other causes such as syndrome of inappropriate antidiuretic hormone secretion and adrenal insufficiency excluded. He was treated with cautious hypertonic saline correction and levothyroxine. Over the following weeks, serum sodium and thyroid function normalized, accompanied by dramatic clinical recovery: cognition improved (Hindi Mental State Examination: 28/30), frailty decreased (Clinical Frailty Scale: 6 to 4), and independence in daily activities improved from 2/6 to 6/6. Unlike previous reports, this case demonstrates a geriatric viewpoint and near-complete reversal of geriatric syndrome and prolonged geriatric functional decline following correction of hypothyroidism-associated hyponatremia, highlighting the need to consider subtle endocrine abnormalities as fully reversible causes of decline in older adults.