Pathophysiology of primary Raynauds Phenomenon with secondary RP
Primary RP: individuals without RP exposed to cold experience increased sympathetic adrenergic input (vasoconstriction) to the cutaneous vasculature as well as increased alpha 2c adrenoreceptor sensitivity. Activation of these receptors on vascular smooth muscle cells results in decreased blood flow through the digital arteries and arteriovenous anastomoses; this helps to divert blood flow and guard against excessive cutaneous heat loss. Nutritional blood flow to the skin supplied by capillary loops distal to the arteriovenous anastomoses, however, is not affected. In primary RP, there is increased basal sympathetic adrenergic tone as well as increased alpha 2c adrenoreceptor activity, even at neutral temperatures. In cold environments, this adrenergic input is heightened and affects not only the arteriovenous anastomoses most prominently but also the digital arteries and veins, and less prominently, the nutritional blood flow through the distal capillary loops. Nutritional blood flow in primary RP is diminished, but preserved, due to intact endothelial function.
Secondary RP: in patients with secondary RP, underlying vascular disease may disrupt the normal mechanisms responsible for the control of vessel reactivity. Examples include impaired endothelial vasodilatory function, diminished nitric oxide release, and increased generation of factors, such as endothelin or ultra-large von Willebrand factor. Furthermore, patients with systemic sclerosis (SSc) may have evidence of intimal proliferation and abnormal platelet adhesion to the endothelium, resulting in reduced vessel lumen size. Consequently, blood flow through the distal capillary loops may be severely decreased in secondary RP, resulting in tissue injury.
Pearl: primary RP should not cause digital ulcerations (preserved nutritional blood flow to the skin) . The presence of digital ulcerations and/or infarcts should prompt further evaluation for secondary causes of RP.
