A case of hyponatraemia secondary to vitamin D deficiency

Hyponatraemia and Vitamin D deficiency are common conditions in older adults. Both conditions cause bone fragility and gait abnormalities, which are risk factors for falls and poor health outcomes in older adults. Vitamin D deficiency is a risk factor for osteoporosis and increases the risk for fragility fractures. Hyponatraemia, the commonest electrolyte abnormality, causes bone resorption and contributes to falls by impairing cognition and by causing gait abnormalities. Sodium homeostasis is complex and the syndrome of inappropriate antidiuretic hormone secretion (SIADH), a diagnosis of exclusion, is one of the most common causes of hyponatraemia. Instability is a feared geriatric syndrome, as falls can have devastating consequences for the older adult, leading to significant morbidity and mortality. Previous studies have shown that patients with hyponatraemia had a higher rate of vitamin D deficiency and, conversely, those with vitamin D deficiency had a higher rate of hyponatraemia. The exact pathophysiological mechanism behind this correlation is unclear but may involve bone derived hormone fibroblast growth factor 23 and the renin-angiotensin-aldosterone system. A case of an 83-year-old Asian female, who presented with an osteoporotic intertrochanteric femoral fracture following a fall, is presented. She was found to have chronic hyponatraemia and was subsequently diagnosed with SIADH due to vitamin D deficiency.