Clinical Manifestations

Sickle-cell disease can be diagnosed prenatally by a procedure known as amniocentesis. After birth the diagnosis is generally made by hemoglobin electrophoresis using cord or peripheral blood. Early diagnosis is now encouraged because of the benefits of new preventive therapies for infection.

Sickle-cell anemia is characterized clinically by a chronic hemolytic anemia and recurrent states called crises. These crisis states are further divided into three types: pain, sequestration, and aplastic.

Pain crisis is the most common and occurs on the average of three times a year. It first presents after 6 months of life when the level of fetal hemoglobin has decreased to a low level. At this age the first signs are often a painful inflammation of the bones of the hands or feet, known as the hand-foot syndrome. Older patients generally develop a recurrent syndrome of joint, back, abdominal, or long-bone pain, which may last for approximately 7 days. Other serious manifestations of vascular occlusion include strokes, heart attacks, leg ulcers, priapism, and pulmonary infarcts.

Splenic sequestration occurs when a large portion of the red cell mass becomes trapped in the spleen, resulting in acute shock. With age, recurrent vascular occlusion of small blood vessels in the spleen results in functional destruction of this organ. Because the spleen is required for destruction of certain types of bacteria, patients with sickle-cell anemia are at increased risk of bacterial infections.

In rare instances, the blood-forming bone marrow becomes exhausted or suppressed for short periods of time, resulting in an acute reduction in red blood cells. This is known as red cell aplasia. This is a temporary condition but one that may require blood transfusions until the bone marrow recovers.

By contrast, sickle-cell trait occurs when individuals' genes carry only one hemoglobin S gene. These persons are phenotypically normal in most respects, although sickling has occasionally been reported to occur in these individuals at high altitudes or low oxygen tension, resulting in splenic infarction. Bleeding from the kidney and a gradual decrease in the concentrating ability of the kidneys have also been shown to occur with increased frequency in people with sickle-cell trait. This condition is almost always benign in nature, however. Nevertheless, concerns have been raised recently that individuals with sickle-cell trait are at increased risk for acute muscle destruction and sudden death. These reports require further confirmation and are highly controversial.

Various other hemoglobins have been shown to sickle in a manner similar to hemoglobin S. Careful chemical analysis is required to differentiate these from sickle hemoglobin.

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