Correlation of parameters of urinary excretion with serum osmolality among patients with psychosis, intermittent hyponatremia, and polydipsia (PIP syndrome).

Nine patients (seven men and two women, mean age 36.3 +/- SD 6.7 years), six of whom had schizophrenic disorders, two of whom had bipolar disorder (manic-depressive illness), and one of whom had schizoaffective disorder, manifested psychosis, intermittent hyponatremia, and polydipsia (PIP syndrome). Their stable pattern of hyposthenuria allowed us to predict 24-hr urinary volume on the basis of estimated daily urinary creatinine and early morning urinary creatinine concentration. Lithium and carbamazepine (Tegretol) had little, if any, effect on polyuria. Correlations of parameters of urinary excretion with serum osmolality among our nine PIP patients failed to implicate water consumption as the exclusive cause of serum hypoosmolality and attendant complications usually ascribed to "water toxicity" in the PIP syndrome. Discussed, also, is the overlap of the clinical and laboratory features of the PIP syndrome with the clinical and laboratory features of both diabetes insipidus and the syndrome of inappropriate antidiuresis.