A 30-year-old woman comes to the physician complaining of a significant increase in her daily urinary volume and intense thirst. The symptoms started a few weeks ago, and she has to get up frequently at night to urinate and drink fluids. She has no other medical problems. The patient does not use tobacco, alcohol, or illicit drugs and has no known drug allergies. Her mother developed diabetes mellitus as an adolescent. Temperature is 36.7 C (98 F), blood pressure is 110/70 mm Hg, pulse is 75/min, and respirations are 15/min. Fasting serum laboratory results are as follows: After 6 hours of water deprivation, laboratory results are as follows:
One hour after the subcutaneous administration of arginine vasopressin, the urine osmolality is 395 mOsm/kg. Which of the following is the most appropriate treatment for this patient?

Question

A 30-year-old woman comes to the physician complaining of a significant increase in her daily urinary volume and intense thirst.  The symptoms started a few weeks ago, and she has to get up frequently at night to urinate and drink fluids.  She has no other medical problems.  The patient does not use tobacco, alcohol, or illicit drugs and has no known drug allergies.  Her mother developed diabetes mellitus as an adolescent.  Temperature is 36.7 C (98 F), blood pressure is 110/70 mm Hg, pulse is 75/min, and respirations are 15/min.  Fasting serum laboratory results are as follows:  After 6 hours of water deprivation, laboratory results are as follows:
 One hour after the subcutaneous administration of arginine vasopressin, the urine osmolality is 395 mOsm/kg.  Which of the following is the most appropriate treatment for this patient?

Quizplus · Accepted Answer

11ec25c8_d3a4_9c19_bc81_c1953e0c4bab_MD0003_00 This patient has polyuria, polydipsia, and mild hypernatremia/hypertonicity. Polyuria in the nonhospitalized patient can be due to diabetes mellitus, primary polydipsia, and diabetes insipidus. This patient's normal serum glucose makes diabetes unlikely. Primary polydipsia is due to increased water intake that surpasses the kidney's ability to excrete it. The increased water leads to hyponatremia (sodium <137 mEq/L), a very dilute urine (osmolality <100 mOsm/kg), and urine osmolality < serum osmolality. This patient's sodium >145 mEq/L and urine osmolality < serum osmolality favor diabetes insipidus (DI). DI can be central (decreased antidiuretic hormone [ADH] secretion from the pituitary) or nephrogenic (normal ADH levels with renal ADH resistance). Central DI patients usually do not have an intact thirst mechanism and can have serum sodium >150 mEq/L. Nephrogenic DI patients usually have an intact thirst mechanism with lower serum sodium (~145 mEq/L). However, some cases may not be clinically obvious. A water deprivation test can distinguish between central and nephrogenic DI and also definitively exclude primary polydipsia. The patient must first abstain from water for at least 2-3 hours. The serum and urine osmolality are measured periodically. Urine osmolality >600 mOsm/kg suggests primary polydipsia due to intact ADH and ability to concentrate urine in the absence of water intake. Patients with continued dilute urine likely have DI. These patients then receive desmopressin to distinguish between central and nephrogenic DI. Central DI typically has >50% (sometimes up to 200%-400%) increase in urine osmolality with desmopressin. Nephrogenic DI has minimal change in urine osmolality with desmopressin. This patient's increased urine osmolality from 132 to 395 mOsm/kg is consistent with central DI. The preferred initial therapy is desmopressin, given intranasally (preferred) or orally. (Choice A) Demeclocycline is used for treating syndrome of inappropriate antidiuretic hormone (SIADH). It inhibits the ADH-mediated aquaporin insertion in the cortical collecting tubule and helps dilute the urine. However, SIADH causes hyponatremia with a concentrated urine (urine osmolality > serum osmolality). (Choice C) Hydrochlorothiazide (HCTZ) is not as effective as desmopressin as monotherapy for central DI. HCTZ can be combined with desmopressin for an additive effect. However, HCTZ is preferred for nephrogenic DI. HCTZ causes mild volume depletion that increases proximal water and sodium reabsorption. (Choice D) Psychotherapy is helpful in treating patients with primary (psychogenic) polydipsia. However, psychotherapy is not effective in managing central DI. In addition, this patient's water deprivation test is not consistent with primary polydipsia. (Choice E) Tolvaptan is a V2 vasopressin receptor antagonist that causes a selective water loss in the kidney without affecting sodium or potassium excretion. Due to its cost and side effects (eg, increased liver enzymes), it is usually reserved for significant hypervolemic (due to heart failure) or euvolemic (due to SIADH) hyponatremia that does not improve with standard therapy (eg, fluid restriction). Educational objective: A water deprivation test can distinguish between central and nephrogenic diabetes insipidus (DI) and also definitively exclude primary polydipsia. Administration of desmopressin after water deprivation can distinguish between central and nephrogenic DI. Patients with central DI increase their urine osmolality by at least 50% following the administration of desmopressin acetate tablets; patients with nephrogenic DI will not show much change. Desmopressin (intranasal form preferred) is the first-line treatment for central DI. References: Clinical review: Current state and future perspectives in the diagnosis of diabetes insipidus: a clinical review. (http://www.ncbi.nlm.nih.gov/pubmed/22855338) Treatment of neurogenic diabetes insipidus. (http://www.ncbi.nlm.nih.gov/pubmed/22071315)

A 30-Year-Old Woman Comes to the Physician Complaining of a Significant