3. CT scan of head. Obtain if central lesion suspected.
4. Urinary concentrating ability (water deprivation test). In young children, this test should be completed in-hospital to allow for monitoring of body weight and electrolytes (exclude hypernatremia). Impose water restriction while assessing urine osmolality, body weight, and vital signs. Terminate test if tachycardia or hypotension develops. In these children, if administration of nasal desmopressin acetate (DDAVP)causes an increase in urine osmolality, a search for central or neurogenic cause of ADH insufficiency is indicated.
V. Plan. Keep a voiding diary (volume and timing of each urination during typical day). Initial evaluation with urinalysis and urinary volumes will differentiate patients with normal urinary volume yet abnormal urinary patterns secondary to voiding dysfunction from those with polyuria secondary to poor concentrating ability or osmotic polyuria (glucosuria).
A. Voiding Disorder. In children with normal urinary volumes, urine specific gravity and osmolarity, and urinary tract imaging, management consists of timed voiding to empty bladder, anticholinergic medication (oxybutynin, tolterodine), and behavioral modification.
B. Renal Maldevelopment. Refer to pediatric nephrologist.
C. Obstructive Nephropathy. Refer to pediatric urologist.
D. Neurogenic Diabetes Insipidus. Refer to pediatric neurologist.
VI. Problem Case Diagnosis. The 4-year-old boy had renal insufficiency secondary to obstructive uropathy (posterior urethral valves). There was no history of excessive fluid intake. Abdominal ultrasound scan showed hydronephrosis, and VCUG showed posterior urethral valves. Patient underwent transurethral ablation of valve leaflets.
VII. Teaching Pearl: Question. What is the difference between nephrogenic and neurogenic diabetes insipidus?
VIII. Teaching Pearl: Answer. Nephrogenic diabetes insipidus results from impaired tubular response to vasopressin and can be hereditary (X-linked or autosomal) or acquired (sickle cell disease, obstructive nephropathy, interstitial nephritis, renal insufficiency). Neurogenic diabetes insipidus result from vasopressin insufficiency, caused by a CNS lesion such as tumor, infection, or trauma. This form of diabetes insipidus responds to exogenous vasopressin (DDAVP).
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