A rare inherited kidney disorder characterized low blood magnesium and high urine calcium levels as well as nystagmus
* Low blood magnesium level * High blood calcium level * Excess urination * Nystagmus * Recurring tetany
* Diuretic use * Primary polydipsia –Usually in middle-aged, anxious women –Psychiatric illnesses due to increased water intake (e.g. psychogenic polydipsia) –May be due to hypothalamic lesions in the thirst centers (e.g., sarcoidosis) * Chronic lithium use –20% of patients develop polydipsia * Central diabetes insipidus –Due to decreased output of antidiuretic hormone –May be idiopathic, familial, autoimmune, or due to head trauma, infiltrative diseases (e.g., sarcoidosis, granulomas, Langerhans cell histiocytosis), pituitary tumors (intrasellar, suprasellar), or ischemic or hypoxic encephalopathy * Nephrogenic diabetes insipidus –Due to decreased response of the kidneys to antidiuretic hormone –May be idiopathic, familial, or due to drugs (e.g., colchicine, fluoride, phenothiazine), chronic renal disease, hypercalcemia, hypokalemia, sickle cell disease * Uncontrolled diabetes mellitus –Patients have polydipsia and subsequent polyuria secondary to high sugar levels
Routine tests include a CBC, sedimentation rate, urinalysis, urine culture and colony count, chemistry panel, thyroid panel, and x-rays of the skull and long bones. The 24-hr intake and output should be measured. A serum and urine osmolality will be helpful, as would a spot urine sodium. If pituitary diabetes insipidus is suspected, a CT scan of the brain and tests for pituitary hormones should be done. The intake and output before and after Pitressin® may be measured. If renal disease is suspected, the urinary sediment should be examined microscopically and renal biopsy may be necessary. An endocrinologist and nephrologist should be consulted before undertaking expensive diagnostic tests.