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| Copyright © 2003 The Diabetes Insipidus Foundation, Inc. | |
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Nephrogenic Diabetes Insipidus
(NDI)
and the Collecting System Patients with NDI may have dilated collecting systems on imaging studies. The severity of the dilatation is influenced by the amount of urine passed per day, the age of diagnosis and management of the NDI, and the presence or absence of obstruction. Dilatation, when present, usually does not cause functional compromise. Even marked dilatation as described by Stevens, et al. in a 15 year old who did not progress with time and normal renal parenchymal thickness was present (1). Although renal function was not mentioned, these authors recommended doing serial ultrasound evaluations of the urinary tract in children with NDI. We disagree with this approach. As shown by Tank et al. the extent of dilatation of the urinary tracts may diminish with appropriate medical management (2). Five children were evaluated by Tank et al. for increased urination and had large bladders and hydro-ureter nephrosis (dilated upper collecting systems). Two of these children had NDI which was diagnosed at three and seven months (2). With appropriate medical management, their dilated urinary tracts as shown on intravenous pyelograms, returned to normal. There are only a few case reports of patients with NDI and presumed "functional" bladder outlet obstruction. Two siblings diagnosed and treated at five and seven years respectively had progressive dilatation of their upper urinary tracts with reduced renal function (3). Urologic studies did not reveal anatomic obstruction and the upper tract changes were attributed to "functional" obstruction secondary to the passage of large urine volumes. In addition, these children may have maintained high bladder sphincter pressures in an attempt to stay dry. Nissenhorn et al. describe a family in which two untreated brothers had polyuria and polydypsia. At 30 years of age one developed macroscopic hematuria associated with fever. His fluid intake was 12 liters per day and renal function was normal. He was treated for a urinary tract infection. Placement of a Foley catheter in the bladder resulted in massive diuresis. Imaging studies revealed dilated upper tracts and an enormous bladder. On hydrochlorothiazide therapy his urine output decreased to eight liters per day. This patient probably had "functional" obstruction secondary to the passage of large urine volumes (4). Operative repair of the suspected anatomical obstruction has been described in patients with NDI (Table 1). A man of 23 years with mild renal dysfunction, dilated upper urinary tracts and large trabeculated bladder which, by post-micturition imaging, did not empty completely was described by Ramsey et al. (5). Although hydrochlorothiazide reduced his urine volumes from 15 liters to 8 liters per day, he underwent bladder neck surgery for presumed outlet obstruction. We are not subsequently told whether the surgery had a positive effect on his renal function. In a further report of two siblings with NDI, the first, a two month old male, failed to thrive and passed large volumes of urine, had salt wasting and was diagnosed with partial obstruction to the right ureterocele (a ballooning out of the mucosa of the lower ureter resulting in compression and obstruction to that ureter). Surgical correction, hydrochlorothiazide, and potassium supplementation allowed this child to thrive (6). His 15 year old female sibling was also evaluated. She had not received diuretic therapy and was passing 10 to 12 liters of urine a day (400 oz.). Massive non-obstructive dilatation of the upper urinary tracts was demonstrated. However, bladder emptying was complete after micturition. An eight year old male with NDI and mild renal insufficiency in whom a "functional" bladder outlet was diagnosed responded well to prolonged drainage through an opening in the bladder (Table 2). Medical treatment was not used even after his renal function had returned to normal (7). Chronic renal failure secondary to NDI is most unusual. Between 1963 and 1992 chronic renal failure was described in only five patients with NDI (8). Four were adults and three were not on any therapy. What does all of this mean? Is there a place for serial urologic evaluation and what role does surgery play? In children presenting with increased urination (polyuria) and dilated bladder or upper tracts initial urologic evaluation to exclude obstruction is required (2). Once an anatomical obstruction is ruled out a careful evaluation of the polyuric disorder is required as children with NDI benefit from early medical intervention (2). There are no prospective studies which serially measure the upper urinary tracts in NDI. Children and adults with untreated NDI are at risk of developing "functional" obstruction. NDI patients with polyuria unresponsive to medical management, failure to thrive, hypertension, urinary tract infection or renal insufficiency should have their renal tracts evaluated. Drainage procedures are required for anatomical obstruction and may rarely be required for "functional" obstruction to prevent deterioration in renal function. References:
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