Suddenly for no apparent reason the penis becomes rigid and painful. These episodes may affect only a part of the penile shaft. The specific mechanisms that precipitate attacks of acute priapism in patients with sickle cell disease are unknown. Acute attacks often start during sleep, occasionally following sexual activity, but frequently no identifiable event is noted. An unusually full bladder is commonly associated with the onset of nocturnal attacks.
Some episodes appear to be triggered or exacerbated by dehydration.
Some patients with priapism have preservation of flow to the glans and spongiosal tissue. Venous outflow from the corpora cavernosa is not always totally occluded as had been earlier postulated. These facts establish the rationale for transfusing normal red cells because these cells can be expected to gradually reach areas of poor circulation. Alternatively some patients may have tricorporal priapism, which is more severe. Presumably, a viscous mass of deoxygenated and damaged red cells develops that further impairs or occludes outflow.