Reset osmostat in a 47-year-old woman with cerebral palsy.

The reset osmostat variation of the syndrome of inappropriate antidiuretic hormone (SIADH) is thought to account for up to one third of SIADH cases. Most commonly, it can cause hyponatremia in patients who are quadriplegic, psychotic, or chronically malnourished, such as those with tuberculosis or alcoholism. Recent case reports have also noted the reset osmostat in several other states, including health. Because the reset osmostat is a diagnosis of exclusion, its workup requires consideration of all other causes of hyponatremia; thus, its investigation can help the primary care physician understand more thoroughly the low-sodium state. Furthermore, as the following case illustrates, its diagnosis can have important consequences for the overall management of a patient’s fluid and nutritional status.