Idiopathic edema usually occurs in premenopausal women, typically from 20 to 40 years of age.
Pathogenesis: unclear. There appears to be increased orthostatic fluid retention associated with venous pooling and/or shifting of intravascular volume into the interstitial space.
Possible associations:
(1) diuretic use or abuse
(2) hormonal factors such as oral contraceptives
Features:
(1) exclusion of systemic disease
(2) discomfort in areas of fluid accumulation
(3) headaches
(4) weight gain throughout the day
change in weight during the day in kg =
= ((weight in the evening) - (weight in morning with an empty bladder and before fluid intake)
A change > 0.7 kg supports the diagnosis of idiopathic edema.
A more complex exam is the water loading test which entails drinking non-iced water at 20 ml/kg body weight (up to 1,500 mL) and then measuring urine output over several hours. The test is conducted over 2 days, with the patient staying erect on day 1 and being recumbent on day 2. In idiopathic edema the urine output is < 55% of water intake while erect and > 65% when recumbent.
