Solution to "Was It the Drinking Binge?"

Robert M. Centor, MD; George M. Solomon, BS, MD


May 09, 2008

This is the solution to a case we presented recently. You may review the case here.

Solution and Discussion

The patient's altered mental status is likely secondary to her acute hyponatremia. Therefore, the central question for work-up and management is: What is the cause of her electrolyte abnormality?

Hyponatremia is best approached systematically when evaluating a patient, and the differential diagnosis is easily narrowed by determining the patient's osmolar state. This patient's osmolarity is 264 mOsm/L; therefore, we conclude that the patient is hypoosmolar. This value demonstrates true hyponatremia and excludes pseudohyponatremia.

In considering hyponatremia, it is important to remember that this problem is caused by excess water. We must determine why the patient is not excreting the excess water. After determining her osmolar state we assess the volume status, as different approaches are necessary for treating hypovolemia, edematous states, and euvolemia. Note that hypovolemic patients can still have excess water.

This patient appears euvolemic on the basis of clinical evidence, including her normal blood pressure, lack of edema, and moist mucous membranes. We first must exclude adrenal insufficiency, hypothyroidism, chronic kidney disease, and the use of thiazides.

After excluding these etiologies, we must check the renal response. If the urine is dilute, the problem stems from intake of dilute fluids that the patient is unable to excrete. In fact, this patient did have dilute urine, with a urine osmolality of only 45 mOsm/L.

Hyponatremia with dilute urine can occur with psychogenic polydipsia. In this condition, the patient drinks water excessively, exceeding the kidneys' ability to produce urine; thus, the water intake dilutes the serum, resulting in hyponatremia.

Hyponatremia can also occur in dedicated beer drinkers (so called beer drinker's potomania) or in persons following the "tea and toast" diet. In these 2 conditions, the patient takes in very little solute in comparison with the water intake.

This patient needed to excrete 45 mOsm for each liter of urine. Unfortunately, beer does not provide the necessary solute to allow excretion of the fluid intake because it has no protein and little salt. This syndrome only occurs in dedicated beer drinkers who eschew solid food. Thus, the urine output is constrained by the available solute.

The patient responded to intravenous saline. The salt in the intravenous fluids allowed an increase in urine output, which allowed the excretion of the excess intravascular water.

Read and participate in the discussion of this case here,and watch for another new case soon.


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