An increased water intake characterizes primary polydipsia. The patient may also consistently complain of a large volume of urine excreted which often exceeds 40-50 mL/kg body weight.
Primary polydipsia can occur in patients with psychiatric illnesses, including bipolar disorder, schizophrenia, schizoaffective disorder, anxiety, and psychotic depression.
Hyponatremia can be present in primary polydipsia due to inadequacy of the kidney to excrete excess fluid resulting in retained water. Excess fluid intake also contributes to this. It is characterized by sodium levels less than 135 mEq/L.
Primary polydipsia presents with normal or decreased plasma osmolality (≤280 mOsm/kg). This differentiates it from diabetes insipidus, which presents with an increased plasma osmolality (≥300 mOsm/Kg).
Primary polydipsia patients present with dilute urine. Labs will reveal a decreased urine osmolality (less than 100 mOsm/kg). Urine osmolality will be less than serum osmolality.
Water restriction through a water deprivation test will cause a significant rise in urine osmolality (>700 mOsm/kg) in normal physiology and primary polydipsia. This will distinguish primary polydipsia from diabetes insipidus, which presents with no change or only a slight increase in urine osmolality.
Water restriction is the ideal treatment for patients with primary polydipsia.
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