Diabetes insipidus and malignant B-cell lymphoma

Dear Sirs, I would like to point out that the case report from Dr. Breidert et al. [[1]] does not necessarily describe a patient with diabetes insipidus.

Very unusual for this diagnosis would be the clearly decreased (serum-) osmolality at the start of the test (268 mOsmol/kg) and a normal value after 10 hours of water deprivation (293 mOsmol/kg). An exact interpretation can only be given with the data of the weight loss and urine production during the test. However, the information in the case report points rather to a diagnosis of ``psychogenic'' polydipsia (after drinking a lot of cold coca cola to ease the pain on swallowing). The diagnosis of diabetes insipidus requires the demonstration of an increased serum osmolality. If this is not possible during a water deprivation test of adequate length (typically after an increased liquid supply and a decreased osmolality in the beginning of the test) a Hickey-Hare test has to be performed (in order to achieve an increased serum osmolality).

References

• 1 Breidert M, Schimmelpfennig C, Kittner Th, Helwig A, Ehninger G. Diabetes insipidus in a patient with a highly malignant B-cell lymphoma and stomatitis.  Exp Clin Endocrinol Diabetes. 108 54-58 2000;