Idiopathic edema is a syndrome of fluid retention with swelling of the face, hands, trunk, and limbs, occurring in premenopausal women in the absence of cardiac, hepatic, or renal disease [1-4]. Diabetes, obesity and emotional problems (including depression and neurotic symptoms) are commonly part of this syndrome [5,6]. There is also an association with purging behaviors (use of diuretics, laxatives, or vomiting) to achieve weight loss, which has led some authors to question whether idiopathic edema is truly an independent entity .
Three major theories — each of which may apply to some patients — have been proposed to explain the fluid retention in idiopathic edema: capillary leak; refeeding; and diuretic-induced edema.
Capillary leak — Many women with idiopathic edema have an abnormal response to assumption of the upright posture. Normal subjects develop a mild degree of plasma volume depletion in this setting due to pooling of extracellular fluid in the lower extremities. As a result, there is a fall in urinary sodium excretion  and a daytime weight gain that averages 0.5 to 1.5 kg [1,2]. In comparison, women with idiopathic edema lose much more fluid from the vascular space with standing , leading to often marked elevations in the release of the "hypovolemic" hormones renin, norepinephrine, and ADH, and to a larger morning-to-evening weight gain that can exceed 5 kg in severe cases [1-3].
These observations have led to the suggestion that idiopathic edema may represent a capillary leak syndrome, in which increased capillary permeability favors the movement of fluid out of the vascular space, a response that is exaggerated by gravity when standing . This primary tendency to plasma volume depletion also explains why the jugular venous pressure is in the low-normal range in idiopathic edema and why pulmonary edema does not occur, even in the presence of marked peripheral edema. (See "Idiopathic systemic capillary leak syndrome".)
The factors responsible for fluid leakage out of the capillaries are not well understood: either altered capillary hemodynamics or, in selected case, primary capillary injury could be responsible . It is possible, for example, that dilatation of the precapillary sphincter plays a central role by permitting more of the systemic pressure to be transmitted to the capillary, thereby increasing the capillary hydraulic pressure. Such a response could be humorally mediated. Women with idiopathic edema often have impaired hypothalamic function, resulting in abnormal release of prolactin, luteinizing hormone, and perhaps other hormones .