Pathogenesis

The most common precipitating factor for painful crisis in Jamaica is skin cooling, which is not known to promote sickling but is well established as a cause of reflex shunting of blood away from the skin. Genotypes of sickle cell disease associated with a reduction in intravascular sickling such as homozygous sickle cell disease with homozygous a+-thalassemia and sickle cell-b°-thalassemia result in more frequent painful crises. The distribution of bone pains shows a significant excess of a bilateral symmetrical pattern, with pain often involving both knees simultaneously or developing within hours. These observations are difficult to explain by a mechanism of random vaso-occlusion. A new theory more consistent with these findings envisages the painful crisis as resulting from a centrally mediated reflex shunting of blood away from the bone marrow so that the nutrient supply is no longer adequate to supply the high metabolic demands, resulting in marrow necrosis. It is believed that the avascular necrosis of bone marrow does not induce acute pain but is associated with a variety of sensations, reported as numbness, heaviness, and paresthesia, representing a prodrome of the painful crisis. The subsequent inflammatory response to dead bone marrow with increased vascularity and outpouring of inflammatory exudate serve to increase intramedullary pressure and cause the severe pain characteristic of the painful crisis.

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