Primary polydipsia

In three patients with chronic schizophrenia and primary polydipsia given clonidine in doses of up to 800 micrograms/day for 2-5 months, blood pressure and pulse fell significantly in a dose-dependent manner, but fluid intake, as assessed by measurements of weight and 24-hour urine volume, was not affected (9). Hypotension and bradycardia limited the extent to which the dose of clonidine could be increased. The lack of effect of clonidine on polydipsia in this small sample and the inconsistent results of two other recent studies have provided little overall support for using clonidine to treat primary polydipsia associated with schizophrenia. 

Effects of clonidine in schizophrenic patients with primary polydipsia three single case studies. Prog... 

In hypoosmotic hyponatremia with a normal volume status, the most common etiologies are the syndrome of inappropriate ADH (SIADH), primary polydipsia, hypothyroidism, and adrenal insufficiency (see Figure 46-2). SIADH is usually a result of ectopic or otherwise inappropriate ADH production arising from a variety of conditions (see Chapters 45 and 50) and results in excessive H2O retention. SIADH is often diagnosed when a urine osmolality that is greater than plasma osmolality (usually by more than >i00 mOsmol/kg) is observed in the setting of hyponatremia, but only when renal, adrenal, and thyroid functions are normal. Hypothyroidism impairs free H2O excretion, whereas in adrenal insufficiency, Na" is lost in preference to IC reabsorption. Finally, euvolemic hyponatremia can be... 

Psychogenic or Primary Polydipsia. A chronic, excessive intalce of water suppresses AVP secretion and produces hypotonic polyuria. The polyuria and polydipsia are usually not as sustained as in HDI or NDI nocturnal polyuria also is less frequent. Psychogenic factors are most commonly associated with this disorder, but hypothalamic disease affecting the thirst center may be a cause. Drugs also can affect the thirst center and result in primary polydipsia. 

Document polyuria (urine volume >2.5L/day) and exclude glycosuria. If desired, creatinine excretion can be measured as an estimate of completeness of urine collections snbstances that inflnence ADH secretion should be avoided (e.g., nicotine, alcohol, and caffeine). If plasma osmolality is >295 mOsm/kg or if serum sodium concentration >145mmol/L, primary polydipsia is unlikely proceed with the overnight water deprivation test (Box 50-9) or the hypertonic saline infusion test (Box 50-10). 

Overnight water deprivation test (Box 50-9) If the ratio of urine to plasma osmolality is <1.5 at the end of the test, primary polydipsia is unlikeiy. Measure plasma and urine osmolalities and plasma ADH concentrations at the end of the test use these relationships to differentiate normal, nephrogenic, or hypothalamic diabetes insipidus, and psychogenic polydipsia. If urine osmoiahty is <400 mOsm/kg at the end of the test, give 5 U of aqueous vasopressin subcutaneously. If urine osmolality increases >10%, hypothalamic diabetes insipidus is probable if urine osmolality does not increase, nephrogenic diabetes insipidus is highly probable. 

Bayiis, P, Gaskill M, Robertson G, Vasopressin secretion in primary polydipsia and cranial diabetes insipidus. Quart J Med NS 1981 50 345-58. 

Because it is stable, desmopressin is preferred for treatments especially if pressor effects are not desired. The primary indication for therapy is central diabetes insipidus, a disorder that results when ADH secretion is reduced and that is characterized by polydipsia, polyuria, and dehydration. Desmopressin is also used to reduce primary nocturnal enuresis, or bedwetting, in children. It is useful in people with mild hemophilia A or with some types of von Willebrand s disease, in which von Willebrand s factor is present at low levels. In these cases, desmopressin is given when excessive bleeding occurs or before surgery to help reduce bleeding indirectly by increasing the amounts of coagulation factors. 

The differential diagnosis of euvolemic hypotonic hyponatremia also includes primary or psychogenic polydipsia. Patients with this... 

Primary hyperaldosteronism (Conn s syndrome) is rare. In most cases, the disease is due to a single adrenocortical adenoma. Patients may present with polydipsia and polyuria, symptoms of neuromuscular abnormalities such as weakness, paraeslhesiae and tetany, and hypertension. All symptoms other than hyjjcrtcnsion are attributable to potassium depletion. 

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