A 6-week-old term boy is brought to the office due to increased fussiness and poor weight gain. The patient has several wet diapers per day. His anterior fontanelle is flat and mucous membranes are dry. Laboratory results include the following: Urinalysis shows a specific gravity of 1.002. Which of the following is the most appropriate treatment for this patient's condition?

Question

A 6-week-old term boy is brought to the office due to increased fussiness and poor weight gain.  The patient has several wet diapers per day.  His anterior fontanelle is flat and mucous membranes are dry.  Laboratory results include the following:  Urinalysis shows a specific gravity of 1.002.  Which of the following is the most appropriate treatment for this patient's condition?

Quizplus · Accepted Answer

11ec160b_3b52_dbc4_9249_bdb0e5f37e02_MD0001_00 This dehydrated infant (eg, flat fontanelle, dry mucous membranes, hypernatremia) is inappropriately producing dilute urine (eg, low urine specific gravity [<1.006]) in large quantities (eg, several wet diapers daily) despite having high levels of ADH, which is consistent with nephrogenic diabetes insipidus (NDI). NDI is caused by resistance to antidiuretic hormone (ADH, or vasopressin) within the renal collecting ducts. Although NDI in adults is commonly due to medications (eg, lithium), in children, it is typically due to congenital mutations involving the vasopressin (V2) receptor or aquaporin 2 channel. ADH is secreted when serum osmolality is high (eg, water deprivation) or extracellular volume is low (eg, dehydration). Normally, ADH increases water reabsorption in the renal collecting ducts, which increases urinary concentration (eg, high urine osmolality and specific gravity) and lowers serum sodium, serum osmolality, and urinary volume. Infants with NDI cannot freely replace ongoing water losses, and early diagnosis and treatment is essential for preventing associated mental and physical growth retardation. Treatment aims to minimize urinary water loss and includes frequent water supplementation and, paradoxically, thiazide administration (eg, hydrochlorothiazide). Thiazides appear to reduce renal water losses in NDI by inducing a mild volume depletion that increases sodium and water reabsorption in the proximal tubule. This decreases the total amount of water delivered to the collecting ducts, allowing for better retention of supplemental water. (Choice A) Desmopressin (an ADH analog) is used to treat central diabetes insipidus, a disorder caused by deficient ADH secretion by the hypothalamus and posterior pituitary. Central diabetes insipidus is associated with low, rather than high, ADH levels. (Choice C) Hydrocortisone can be used to treat adrenal insufficiency, which may also present with hypovolemia and high ADH levels. However, renal ADH response is intact; therefore, hyponatremia and high urine specific gravity would be expected (Choice D) Severe hyperglycemia from diabetes mellitus can lead to polyuria and dehydration; however, increased urinary glucose would cause high urine specific gravity and urine osmolality. (Choice E) Salt tablets can treat the syndrome of inappropriate ADH, which is associated with hyponatremia and high urine specific gravity. Educational objective: Nephrogenic diabetes insipidus is characterized by polyuria, dilute urine (low urine specific gravity), hypernatremia, and high antidiuretic hormone. Treatment includes thiazide diuretics and replacement of water losses. __________ References: Paradoxical antidiuretic effect of thiazides in diabetes insipidus: another piece in the puzzle. (http://www.ncbi.nlm.nih.gov/pubmed/15504949) Management of diabetes insipidus in children. (http://www.ncbi.nlm.nih.gov/pubmed/22029022)

A 6-Week-Old Term Boy Is Brought to the Office Due