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Detailed information of NEPHROGENIC DIABETES INSIPIDUS
NEPHROGENIC DIABETES INSIPIDUS
DEFINITION:
An x-linked renal disorder characterized by a complete tubular
unresponsiveness to ADH in males and partial unresponsiveness in
females resulting in the excretion of increased volume of diluted
urine.
EPIDEMIOLOGY:
- incidence: ?
- age of onset:
- risk factors:
- familial - x-linked recessive
- M > F
PATHOGENESIS:
- antidiuretic hormone (ADH) is released by the posterior
pituitary and binds to receptors on the distal tubules and
collecting ducts which increases the permeability of these areas
to water reabsorption -> water flows by passive diffusion from
the tubule into the hypertonic medullary interstitium of the
kidney
- ADH can concentrate urine to an osmolality > 1000 mOsm/L
2. Genetic Defect
- the genetic defect in primary nephrogenic diabetes insipidus
results in the distal tubules and collecting ducts unable to
respond to exogenous or endogenous ADH (defective generation of
cAMP in response to ADH) -> these areas therefore remain
impermeable to water
- in the primary form, there is no loss of medullary
concentrating gradient
- this primary syndrome was first described by Waring et al in
1945
CLINICAL FEATURES:
- present in infancy
- polyuria and polydipsia with episodes of hypernatremic
dehydration
- episodes of pyrexia and vomiting
- failure to thrive
2. Females
- present at a later age with milder symptoms
2. Complications
- mental retardation (due to repeated episodes of hypertonic
dehydration)
- hydronephrosis (due to an excess urine production)
INVESTIGATIONS:
- fast patient until plasma osmolality is >295 mOsm/L and the
ratio of urine/plasma is <1
- give 0.1-0.2 U/kg IM of aqueous ADH (vasopressin)
- measure urine/plasma osmolality q1h x 4
- if ratio remains <1 the diagnosis is made
2. Serum
- normal or increased vasopressin
3. Urine
- osmolality commonly less than or equal to 100 mOsm/L
4. Imaging Studies
- secondary enlargement of kidneys, ureters, and bladder
MANAGEMENT:
- provide adequate fluid and caloric intake
- reduce sodium load and use low sodium formula
- fluids (water or fruit juice) q1-2h during the day and 3
times at night until child can obtain free access to water
2. Medical
- diuretic which works paradoxically by increasing sodium
excretion producing a relative sodium depletion. This enhances
sodium reabsorption in the proximal tubule and thus water
reabsorption. Thus less water is presented to the defective
portion of the tubules
- watch for hypokalemia and use K supplements if needed
2. Indomethacin
- inhibitor or prostaglandin synthesis
- used in patients who fail low sodium diet and diuretic
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Pediatric Database - NEPHROGENIC DIABETES INSIPIDUS
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