Anemia - sickle cell; Hemoglobin SS disease (Hb SS)
Sickle cell disease
Definition - Causes, incidence, and risk factors - Symptoms - Signs and tests - Treatment .
Definition
Sickle cell anemia is an inherited disease in which the red blood cells, normally disc-shaped, become crescent shaped. As a result, they function abnormally and cause small blood clots. These clots give rise to recurrent painful episodes called "sickle cell pain crises.
Causes, incidence, and risk factors
Sickle cell anemia is caused by an abnormal type of hemoglobin called hemoglobin S. Hemoglobin is a protein inside red blood cells that carries oxygen. Hemoglobin S, however, reduces the amount of oxygen inside the cells, distoring their shape. The fragile, sickle-shaped cells deliver less oxygen to the body's tissues, and can break into pieces that disrupt blood flow.
Sickle cell anemia is inherited as an autosomal recessive trait , which means it occurs in someone who has inherited hemoglobin S from both parents. Sickle cell disease is much more common in certain ethnic groups, affecting approximately one out of every 500 African Americans. Someone who inherits hemoglobin S from one parent and normal hemoglobin (A) from the other parent will have sickle cell trait. Someone who inherits hemoglobin S from one parent and another type of abnormal hemoglobin from the other parent will have another form of sickle cell disease, such as thalassemia.
Although sickle cell disease is present at birth, symptoms usually don't occur until after 4 months of age. Sickle cell anemia may become life threatening . Blocked blood vessels and damaged organs can cause acute painful episodes, or "crises." There are several types of crises:
Hemolytic crisis occurs when damaged red blood cells break down
Splenic sequestration crisis is when the spleen enlarges and traps the blood cells
Aplastic crisis results when an infection causes the bone marrow to stop producing red blood cells
These painful crises, which occur in almost all patients at some point in their lives, can last hours to days, affecting the bones of the back, the long bones, and the chest. Some patients have one episode every few years, while others have many episodes per year. The crises can be severe enough to require admission to the hospital for pain control and intravenous fluids.
Repeated crises can cause damage to the kidneys, lungs, bones, eyes, and central nervous system.
Symptoms
Common symptoms include:
paleness
yellow eyes/skin
fatigue
breathlessness
rapid heart rate
delayed growth and puberty
susceptibility to infections
ulcers on the lower legs (in adolescents and adults)
jaundice
bone pain
attacks of abdominal pain
fever
The patient may also have:
bloody urine (hematuria )
frequent urination
excessive thirst
painful erection (priapism; this occurs in 10-40% of men with the disease)
chest pain
poor eyesight/blindness
Signs and tests
Tests commonly performed to diagnose and monitor patients with sickle cell anemia include:
Complete blood count (CBC )
Hemoglobin electrophoresis
Sickle cell test
Patients with sickle cell may have abnormal results on certain tests, as follows:
peripheral smear displaying sickle cells
urinary casts or blood in the urine
Hemoglobin; serum decreased
elevated bilirubin
high white blood cell count
elevated serum potassium
elevated serum creatinine
blood oxygen saturation may be decreased
CT scan or MRI can display strokes in certain circumstances
Treatment
Patients with sickle cell disease need continous treatment, even when they are not having a painful crisis. Supplementation with folic acid, an essential element in producing cells, is required because of the rapid red blood cell turnover.
The purpose of therapy is to manage and control symptoms and to try to limit the frequency of crises.
During a sickle crisis, certain therapies may be necessary. Painful episodes are treated with analgesics and adequate liquid intake. Treatment of pain is critical. Non-narcotic medications may be effective, but some patients will require narcotics.
Hydroxyurea (Hydrea) was found to help some patients by reducing the frequency of painful crises and episodes of acute chest syndrome and decreasing the need for blood transfusions. There has been some concern about the possibility of this drug causing leukemia, but as yet there are no definitive data that Hydrea causes leukemia in sickle cell patients.
Newer drugs are being developed to manage sickle cell anemia. Some of these agents work by trying to induce the body to produce more fetal hemoglobin (therefore decreasing the amount of sickling) or by increasing the binding of oxygen to sickle cells. But as yet, there are no other widely used drugs that are available for treatment.
Bone marrow transplants can be curative, this therapy is indicated in only a minority of patients, predominantly because of the high risk of the procedure (the drugs needed to make the transplant possible are highly toxic) and difficulty in finding suitable donors. Also, bone marrow transplants are much more expensive than other treatments.
Antibiotics and vaccines are given to prevent bacteria infections, which are common in children with sickle cell disease.
Additional treatments may include:
partial exchange transfusion for acute chest syndrome
transfusions or surgery for neurological events, such as strokes
dialysis or kidney transplant for kidney disease
irrigation or surgery for priapism
surgery for eye problems
hip replacement for avascular necrosis of the hip (death of the joint)
gallbladder removal (if there is significant gallstone disease)
wound care, zinc oxide, or surgery for leg ulcers
drug rehabilitation and counseling for the psychosocial complications
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