Symptoms
Clinical symptoms of Schwartz-Barrter syndrome may initially be confusion, headache, weakness and muscle cramps, followed by dizziness, loss of appetite, nausea, vomiting, seizures and disturbances of consciousness up to coma. These symptoms are caused by the excessively increased water retention (water intoxication) and the resulting hyponatremia. In addition, there is weight gain and reduced urine excretion with highly concentrated urine.
The increase in extracellular and intracellular volume increases the risk of fluid accumulation in the brain (brain edema), which can be fatal without treatment. Other edema of the body is not observed, blood pressure and heart rate are normal. In general, however, no symptoms need to occur, i.e. Schwartz-Bartter syndrome can also be asymptomatic.The diagnosis of Schwartz-Barrter syndrome is based on a detailed interview with the patient (anamnesis), the symptoms and the results of laboratory tests of the blood and urine.
During the interview it is important to ask about the amount of drinking and urine and about changes in body weight. An increase of five to ten percent in body weight in a short period of time for unexplained reasons, without edema having occurred, is an important indication of Schwartz-Bartter syndrome. Laboratory diagnostics show a low volume of urine per time, with a high concentration of urine (urinosmolality: >300 mosmol/kg, specific gravity increased) and an unreasonably high concentration of sodium in the urine (> 20 mmol/liter).
Hyponatremia (serum Na+ <135 mmol/l) is evident in the blood due to blood dilution (serum osmolality: <300 mosmol/kg). The determination of the ADH concentration in the blood is not very useful, since the values can be normal or elevated, but do not have to be elevated. However, the values are never lowered, as is the case with other forms of hyponatremia.
Differential diagnosis
The hyponatremia of Schwartz-Bartter syndrome must be distinguished from the hyponatremia of heart failure, nephrotic syndrome and liver cirrhosis, and the hyponatremia of lack of blood plasma volume, e.g. after diarrhea, sweating or taking diuretics, a drug to flush water out of the body.
