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Also known as: '''''IMHA — Autoimmune haemolytic anaemia (AIHA) — Pure red cell aplasia (PRCA)

Also known as: '''''IMHA — Autoimmune haemolytic anaemia (AIHA) — Pure red cell aplasia (PRCA)

Some types of [[IgG]] antibody are able to directly activate the complement cascade but, in most cases, these antibodies are not able to cause intravascular haemolysis of agglutination and they are therefore described as '''incomplete''' antibodies.  These antibodies act as opsonins and, through their interaction with Fc receptors expressed by cells of the hepatosplenic monocyte-phagocyte system (MPS), they promote the uptake and destruction of the red blood cells to which they are bound. These types of antibody therefore cause '''extravascular haemolysis'''.

Some types of [[IgG]] antibody are able to directly activate the complement cascade but, in most cases, these antibodies are not able to cause intravascular haemolysis of agglutination and they are therefore described as '''incomplete''' antibodies.  These antibodies act as opsonins and, through their interaction with Fc receptors expressed by cells of the hepatosplenic monocyte-phagocyte system (MPS), they promote the uptake and destruction of the red blood cells to which they are bound. These types of antibody therefore cause '''extravascular haemolysis'''.

IMHA may occur as a '''primary''' disease with no apparent cause or it may be '''secondary''' to another systemic insult. Possible secondary causes of IMHA include bacterial and parasite infections (including ''[[Babesia canis]]'' in dogs and ''[[Mycoplasma haemofelis]]'' in cats), adverse drug reactions, neoplasia (especially myeloproliferative and lymphoproliferative disease) and live vaccines, although the association between vaccination and immune-mediated disease remains controversial.   

IMHA may occur as a '''primary''' disease with no apparent cause or it may be '''secondary''' to another systemic insult. Possible secondary causes of IMHA include bacterial and parasite infections (including ''[[Babesia canis]]'' in dogs and ''[[Feline Infectious Anaemia|Mycoplasma haemofelis]]'' in cats), adverse drug reactions, neoplasia (especially myeloproliferative and lymphoproliferative disease) and live vaccines, although the association between vaccination and immune-mediated disease remains controversial.   

The majority of cases of IMHA affect only the circulating red blood cells resulting in a strongly [[Regenerative and Non-Regenerative Anaemias|regenerative anaemia]] as the bone marrow stem cells respond to the disease. In a small number of cases, antibodies are produced that affect the stem cells of the [[Erythropoiesis|erythroid lineage]] in the bone marrow, resulting in a non-regenerative anaemia that still bears many of the same clinical features as IMHA. Although the two diseases have been considered separately in the past, they really represent two ends of a spectrum of immune-mediated disease directed at cells of the erythroid line.   

The majority of cases of IMHA affect only the circulating red blood cells resulting in a strongly [[Regenerative and Non-Regenerative Anaemias|regenerative anaemia]] as the bone marrow stem cells respond to the disease. In a small number of cases, antibodies are produced that affect the stem cells of the [[Erythropoiesis|erythroid lineage]] in the bone marrow, resulting in a non-regenerative anaemia that still bears many of the same clinical features as IMHA. Although the two diseases have been considered separately in the past, they really represent two ends of a spectrum of immune-mediated disease directed at cells of the erythroid line.   

====Haematology====

====Haematology====

Affected animals have a reduced [[Packed Cell Volume|packed cell volume]] (PCV) or haematocrit (HCT) and often a reduced haemoglobin concentration.  IMHA causes a strongly [[Anaemia - Introduction|regenerative anaemia]] and evidence of macrocytosis (increased MCV) should be apparent after 48-72 hours in dogs. A blood smear is extremely useful in evaluating cases of IMHA as '''spherocytes''' are often visible. These small, dense red blood cells are formed due to partial phagocytosis of red blood cells by the MPS. Polychromasia should also be visible on a blood smear from an animal undergoing regeneration and reticulocytosis can be confirmed using a supravital stain such as new methylene blue.

Affected animals have a reduced [[Packed Cell Volume|packed cell volume]] (PCV) or haematocrit (HCT) and often a reduced haemoglobin concentration.  IMHA causes a strongly [[Regenerative and Non-Regenerative Anaemias|regenerative anaemia]] and evidence of macrocytosis (increased MCV) should be apparent after 48-72 hours in dogs. A blood smear is extremely useful in evaluating cases of IMHA as [http://www.medvet.umontreal.ca/clinpath/banq-im/hematology/SpherocytesE.htm spherocytes]are often visible. These small, dense red blood cells are formed due to partial phagocytosis of red blood cells by the MPS. Polychromasia should also be visible on a blood smear from an animal undergoing regeneration and reticulocytosis can be confirmed using a supravital stain such as new methylene blue.

Reactive [[Platelet Abnormalities|thrombocytosis]] and leucocytosis may be present with any cause of anaemia.

Reactive [[Platelet Abnormalities|thrombocytosis]] and leucocytosis may be present with any cause of anaemia.

Most mortality occurs in the first two weeks after presentation and, overall, 30-50% of animals would be expected to survive for at least one year after initial treatment for IMHA<ref>'''Idiopathic immune-mediated hemolytic anemia: treatment outcome and prognostic factors in 149 dogs.''' ''Piek CJ, Junius G, Dekker A, Schrauwen E, Slappendel RJ, Teske E.'' J Vet Intern Med. 2008 Mar-Apr;22(2):366-73. Epub 2008 Mar 10.</ref>.  

Most mortality occurs in the first two weeks after presentation and, overall, 30-50% of animals would be expected to survive for at least one year after initial treatment for IMHA<ref>'''Idiopathic immune-mediated hemolytic anemia: treatment outcome and prognostic factors in 149 dogs.''' ''Piek CJ, Junius G, Dekker A, Schrauwen E, Slappendel RJ, Teske E.'' J Vet Intern Med. 2008 Mar-Apr;22(2):366-73. Epub 2008 Mar 10.</ref>.  

==Literature Search==

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|literature search = [http://www.cabdirect.org/search.html?options6=OR&calendarInput=yyyy-mm-dd&occuring1=title&rowId=1&rowId=2&rowId=3&rowId=4&rowId=5&rowId=6&show=all&options1=AND&occuring5=title&options2=OR&occuring4=title&options3=OR&occuring3=title&options4=OR&options5=OR&occuring2=title&publishedend=yyyy&fq=sc%3A%22ve%22&q6=PRCA&q5=%22Pure+red+cell+aplasia%22&it=any&q2=IMHA&q1=%22Immune+Mediated+Haemolytic+Anaemia%22&q4=AIHA&q3=%22Autoimmune+haemolytic+anaemia%22&la=any&publishedstart=yyyy&occuring6=title&y=8&x=45 Immune Mediated Haemolytic Anaemia publications]

|flashcards = [[Small Animal Emergency and Critical Care Medicine Q&A 20]]

 

[[Category:Antibody Mediated Autoimmune Diseases]]

[[Category:Antibody Mediated Autoimmune Diseases]]

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[[Category:Immunological Diseases - Dog]][[Category:Lymphoreticular and Haematopoietic Diseases - Dog]][[Category:Lymphoreticular and Haematopoietic Diseases - Cat]][[Category:Immunological Diseases - Cat]]

[[Category:Expert Review]]

[[Category:Expert Review - Small Animal]]