Spherocytosis

Spherocytosis is an auto-hemolytic anemia (a disease of the blood) characterized by the production of red blood cells (RBCs), or erythrocytes, that are sphere-shaped, rather than bi-concave disk shaped. It is caused by a molecular defect in one or more of the proteins of the red blood cell cytoskeleton, including, spectrin, ankyrin, Band 3, or Protein 4.2. Because the cell skeleton has a defect, the blood cell contracts to its most surface-tension efficient and least flexible configuration, a sphere. The sphere-shaped red blood cells are known as spherocytes.

Though the spherocytes have a smaller surface area through which oxygen and carbon dioxide can be exchanged, they in themselves perform adequately to maintain healthy oxygen supplies. However, they have a high osmotic fragility--when placed into water, they are more likely to burst than normal red blood cells. These cells are more prone to physical degradation. They are most commonly found in immunologically-mediated hemolytic anemias and in hereditary spherocytosis, but the former would have a positive direct Coombs test and the latter would not. The misshapen but otherwise healthy red blood cells are mistaken by the spleen for old or damaged red blood cells and it thus constantly breaks them down, causing a cycle whereby the body destroys its own blood supply (auto-hemolysis).

Symptoms

The spleen's hemolysis results directly in varying degrees of anemia and hyperbilirubinemia, which in turn result in symptoms of fatigue, pallor, and jaundice.

Acute cases can threaten hypoxemia through anemia and acute kernicterus through hyperbilirubinemia, particularly in newborns.Occasionally, the disease will not be noticed until the child is about 4 or 5 years of age. A way to know that someone has the disease, is if they are commonly jaundice.

Chronic symptoms include anemia and splenomegaly, a potentially life-threatening enlargement of the spleen due to its increased activity. Furthermore, the detritus of the broken-down blood cells--bilirubin--accumulates in the gallbladder, and can cause pigmented gallstones or "sludge" to develop. In chronic patients, an infection or other illness can cause an increase in the destruction of red blood cells, resulting in the appearance of acute symptoms, a hemolytic crisis.

Diagnosis

In peripheral blood smears, many of the red blood cells will appear abnormally small and will lack the central pallor--the lighter area in the middle of an RBC as seen under a microscope.

The CBC (cell blood count) laboratory values will show elevated MCHC.

The splenic cords are congested with red blood cells to be destroyed and macrophages of the spleen will show signs of actively destroying erythrocytes (erythrophagocytosis). This will result in an elevated bilirubin level.

The bone marrow in its role of manufacturing red blood cells will display hyperplasia, the increased activity of replacing RBCs. As a result, immature red blood cell--or reticulocyte--counts will appear elevated.

A osmotic fragility test can aid in the diagnosis of spherocytosis.^[1]

Treatment

Acute symptoms

Acute symptoms of anemia and hyperbilirubinemia can indicate treatment with blood transfusions or exchanges. Transfusions treat anemia by adding healthy donor blood to the patient's own, providing needed red blood cells. As the transfused blood does not contain spherocytes, it will not be hemolysed per se, but the overactive spleen may still break down a significant proportion of the transfused blood. Exchanges treat hyperbilirubinemia by replacing some portion of the patient's blood with healthy donor blood, thus removing some portion of the toxic bilirubin.

Chronic symptoms

Chronic symptoms of anemia and splenomegaly typically indicate dietary supplementation of folic acid and eventual treatment by splenectomy, the surgical removal of the spleen.

In longstanding cases in which patients have taken supplemental iron or received numerous blood transfusions, iron overload may be a significant problem, being a potential cause of cardiomyopathy and liver disease. If there is iron overload, chelation therapy with agents such as desferrioxamine may be necessary.

While splenectomy does not affect the shape of the blood cells, it does remove the more obvious physical symptoms of the disorder, as the blood cells are no longer constantly broken down. Though it offers near-immediate relief from symptoms, splenectomy is often not performed until the patient is in late childhood, so as not to hinder the patient's ability to fight off childhood infections. The surgery is often performed laparoscopically. Given that surgery is preplanned, it is highly recommended that patients receive prior Pneumovax-II pneumococcus, conjugated-C meningococcus & Haemophilus influenzae type b vaccinations to combat the patient's new lower tolerance against overwhelming post-splenectomy infection. The Pneumovax needs repeating every six years and the patient should have a yearly influenza vaccine. Prophylactic antibiotics are also given. (See asplenia for further details on these measures).

Underlying disorder

Both measures described above treat the symptoms, not the cause of the disorder. Non-hereditary spherocytosis has several causes, each treated differently. Experimental gene therapy exists to treat hereditary spherocytosis in lab mice; however, this treatment has not yet been tried on humans. See also Hereditary spherocytosis.

See also

• Hereditary spherocytosis
• Anemia
• Blood
• Blood diseases
• Red blood cells
• Hereditary diseases

External links

• Online 'Mendelian Inheritance in Man' (OMIM) 182900
• A short article from WebMD
• A picture of spherocytes from Medline
• A detailed and technical (but good) article from eMedicine

References

1. ^ Won DI, Suh JS (March 2009). "Flow cytometric detection of erythrocyte osmotic fragility". Cytometry B Clin Cytom 76 (2): 135–41. doi:10.1002/cyto.b.20448. PMID 18727072. http://dx.doi.org/10.1002/cyto.b.20448. 

• Kumar, Vinay, Abul Abbas, and Nelson Fausto. "Robbins and Cotran Pathologic Basis of Disease, 7th edition (2004)."
• Schneider, Arthur S. and Philip A. Stanzo. "Board Review Series: Pathology, 2nd edition (2002)."