Aplastic anemia overview

# Overview
Anemia is the condition of having fewer red blood cells than normal, or fewer than needed to function properly. Typically, anemia refers to low red blood cell counts, but aplastic anemia patients have lower counts of all three blood cell types:  red blood cells, white blood cells, and platelets. Bone marrow is a sponge-like tissue inside the bones. It makes stem cells that develop into red blood cells, white blood cells, and platelets. Aplastic anemia is a condition where bone marrow does not produce sufficient new cells to replenish blood cells. The term 'aplastic' means the marrow suffers from an aplasia that renders it unable to function properly.
Red blood cells carry oxygen to all parts of your body. They also carry carbon dioxide (a waste product) to your lungs to be exhaled. White blood cells help your body fight infections. Platelets are blood cell fragments that stick together to seal small cuts or breaks on blood vessel walls and stop bleeding. It's normal for blood cells to die. The lifespan of red blood cells is about 120 days. White blood cells live less than a day. Platelets live about 6 days. As a result, the bone marrow must constantly make new blood cells. If the bone marrow can't make enough new blood cells, many health problems can occur. These problems include arrhythmias, an enlarged heart, heart failure, infections, and bleeding. Severe aplastic anemia can even cause death.

# Historical Perspective
Paul Ehrlich in 1988 made known the notion of aplastic anemia. He narrated the case of a pregnant lady, who died of bone marrow failure. In1904 Anatole Chauffard named this disorder aplastic anemia. In 1920s and 1930s Alice Hamilton and Harrison recognised bone marrow failure in workers who were exposed to benzene in the United States. In the late 1940s and early 1950s, an epidemic of aplastic anemia started showing up in people who were recieving chloramphenicol, and then aplastic anemia has been related to many classes of drugs generally used in medical practice. Neal Young from john hopkins in 1980s introduced an immunosuppressive regimen which proved to be very effective treatment for aplastic anemia.

# Classification
Aplastic anemia may be classified according to blood cell counts into 3 subgroups, moderately severe aplastic anemia or non severe AA (nSAA), severe aplastic anemia (SAA), and very severe aplastic anemia(vSAA).

# Pathophysiology
Bone marrow is a spongy tissue, found within the spongy or cancellous portions of bones. It is higly vascularized and richly innervated Bone marrow is the primary site of hematopoiesis and is composed of hematopoietic cells, marrow adipose tissue, and stromal cells. The most defenitive feature in pathophysiology of aplastic anemia is loss of hematopoietic stem cells. It may be in the form of hematopoietic failure or immune mediated destruction of bone marrow. Drugs, chemicals, viruses, and different kind of mutations change the immunologic appearance of HSCs resulting in autoimmune destruction of marrow cells. AA may develop gradually into other hematologic disorder which include paroxysmal nocturnal hemoglobinuria , myelodysplastic syndromes  and acute myeloid leukemia ). Clonal evolution in AA can occur due to mutations or cytogenetic abnormalities. The genes that are commonly found to be mutated are DMNT3A, ASXL1, BCOR, BCORL1, PIGA.

# Causes
Common causes of aplastic anemia include hepatitis, Epstein-Barr virus, cytomegalovirus, parvovirus B19, and HIV. Medicines, such as Albendazole, Cefadroxil, Chlorpromazine, chloramphenicol , Carbamazepine, Hydroxychloroquine, Methimazole, Orphenadrine, Oxcarbazepine, Phenytoin, Quinine, Phenylbutazone, Sulindac, Sulfadiazine, Sulfasalazine, Valganciclovir hydrochloride. Other causes include radiation, chemotherapy, toxins, such as pesticides, arsenic, and benzene, and metastasis to bone marrow. Less common causes of aplastic anemia are Lupus (SLE), rheumatoid arthritis, .pregnancy, Thymoma, and collagen vascular disease.

# Differentiating  from other Diseases
The primary diagnostic dilemma is differentiating aplastic anemia from a hypocellular myelodysplastic syndrome.

# Epidemiology and Demographics

## Age
People of all ages can develop aplastic anemia. It is more common in adolescents, young adults, and the elderly

## Gender
Men and women are equally likely to develop aplastic anemia

## Race
Aplastic anemia is two to three times more common in Asians

# Risk Factors
Aplastic anemia is a rare but serious blood disorder. Common risk factors in the develpment of aplastic anemia are radiation treatment, drugs and toxin exposure, chemotherapy, PNH, and viral hepatitis. Less common risk factors are pregnancy, benzene, pesticides, rheumatoid arthritis and SLE.

# Natural History, Complications and Prognosis
Aplastic anaemia has a mixed clinical course. Untreated aplastic anemia leads to rapid death, typically within six months. Complications following development of aplastic anemia are infections, bleeding and paroxysmal nocturnal hemoglobinuria. Graft-versus-host disease and graft failure are the possible complications following bone marrow transplant in these patients. Mild cases resolve on their own requiring little or no treatment. Well-matched bone marrow transplants from siblings have been successful in young individuals with a long-term survival rate of 80%-90%

# Diagnosis

## Diagnostic Criteria
Bone marrow biopsy is the gold standard test for the diagnosis of aplastic anemia, These  findings on performing bone marrow biopsy are confirmatory for aplastic anemiahypoplasia with <20% cellularity, normal maturation of all cell line, fat cells and stroma in bone marrow space. Residual hematopoietic cells are morphologically normal and hematopoiesis is not megaloblastic.

## Symptoms
Aplastic anemia is seen as a result of hypoplastic bone marrow causing pancytopenia (anemia, neutropenia, thrombocytopenia). The history and symptoms seen are secondary to these abnormalities.

## Physical Examination
Common physical examination findings of aplastic anemia include pale color, short stature, dyspnea, petechiae ,Purpura, Ecchymoses, Jaundice, Pallor ,bruises. patients can present with, oral leukoplakia, pharyngeal ulcers, necrotizing gingivitis and tonsillitis.

## Laboratory Findings
Patients with aplastic anemia have a hypoplastic bone marrow (<20% cellularity), pancytopenia (transfusion-dependent anemia, thrombocytopenia, and severe neutropenia), a low reticulocyte count, and a normal maturation of all cell lines.

## Imaging Findings
There are no imaging study associated with aplastic anemia.

# Treatment

## Medical Therapy
Treatments for aplastic anemia include blood transfusions, blood and marrow stem cell transplants, and medicines.

## Surgery
There is no surgical treatment for aplastic anemia.

## Prevention
There are no primary preventive measures available for aplastic anemia.