Pediatric emergency medicine trisk 308

If the history and physical examination are not revealing, a urinalysis should be
obtained. In almost all cases of polydipsia, the urine-specific gravity will be low
(less than 1.010). A specific gravity greater than 1.020 usually represents
appropriate thirst. If the urinalysis is abnormal, DM (glucosuria, possibly
ketonuria, and pseudo-hypersthenuria), sickle cell disease (isosthenuric), or an
intrinsic renal disorder (cellular elements and sediment) should be suspected. If
the urinalysis is normal, electrolytes, calcium, and renal function tests may reveal
conditions associated with electrolyte imbalances. Patients with poorly controlled
DM, DI, or nephrogenic DI may have hypernatremia if they are examined when
dehydrated. A hemoglobin electrophoresis may be needed to determine whether
the patient has sickle cell disease. However, patients with sickle cell disease
usually have the diagnosis confirmed before the development of tubular
dysfunction and polydipsia. Because of the high resolution required to diagnose
most intracranial causes, magnetic resonance imaging scan is usually necessary.


TABLE 64.1
CAUSES OF POLYDIPSIA


Diabetes mellitus
Electrolyte imbalances
Hypercalcemia
Hypokalemia
Bartter syndrome
Catecholamine excess
Pheochromocytoma
Neuroblastoma
Ganglioneuroma
Cystinosis
Diabetes insipidus (antidiuretic hormone deficient)

Craniopharyngioma
Pituitary adenoma
Langerhans cell histiocytosis
Head trauma
Sarcoidosis
Leukemia
Infection
Aneurysm
Intraventricular hemorrhage
Hereditary
Drugs
Methylxanthines
Amphotericin B
Diuretics
Lithium
Renal causes
Renal tubular acidosis
Nephrogenic diabetes insipidus
Sickle cell anemia
Interstitial nephritis
Obstructive uropathy
Primary polydipsia
Psychogenic polydipsia


Neurogenic polydipsia

FIGURE 64.1 Diagnostic approach to a child with polydipsia. UA, urinalysis; BUN, blood
urea nitrogen; Cr, creatinine; Ca, calcium.

TABLE 64.2
COMMON CAUSES OF POLYDIPSIA
Diabetes mellitus
Sickle cell anemia
Diabetes insipidus (antidiuretic hormone deficient)
Patients suspected of having primary polydipsia, DI, and nephrogenic DI
require further testing that can be dangerous. Because these tests need to be
performed in a closely supervised, controlled setting, these patients should be
admitted for evaluation.
Patients with primary polydipsia should respond to a water deprivation test by
increasing their urine-specific gravity and osmolality. Patients with DI and
nephrogenic DI should have rapid weight loss while continuing to excrete urine