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Immune Mediated Haemolytic Anaemia (view source)
Revision as of 18:25, 7 March 2022
, 18:25, 7 March 2022no edit summary
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.
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.
Primary IMHA results from the formation of antibodies which are specifically directed against the hosts’ erythrocytes. Secondary IMHA occurs when antibodies directed against non-erythrocyte antigens also attach to RBCs. Antibody coated erythrocytes have a decreased lifespan, they are prematurely removed from the circulation by splenic and hepatic macrophages. Antibodies which fix complement can cause intravascular haemolysis. Primary IMHA is idiopathic. Secondary IMHA, the most common form seen in cats, may be secondary to certain drugs (potentiated sulphonamides, anti-thyroid drugs), lymphoid neoplasia, infection (bacterial, FeLV, haemotrophic Mycoplasma spp). References: [[/en.wikivet.net/NationWide Laboratories|NationWide Laboratories]]
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.
===Laboratory Tests===
===Laboratory Tests===
On presentation, full biochemical and haematological analysis of blood samples are indicated to confirm the diagnosis and to obtain a baseline measurement to assess the efficacy of future treatment. Several tests are also available that have a higher specificity for the diagnosis of IMHA.
On presentation, full biochemical and haematological analysis of blood samples are indicated to confirm the diagnosis and to obtain a baseline measurement to assess the efficacy of future treatment. Several tests are also available that have a higher specificity for the diagnosis of IMHA.
Haematological findings include a moderate to severe anaemia (PCV<16%), marked reticulocytosis, moderate to marked polychromasia, normal or slightly increased plasma proteins, marked leucocytosis, often with a left shift, significant spherocytosis, autoagglutination and thrombocytopaenia. A positive Coombs test supports a diagnosis but the test is subjects to false negative and false positive results. Autoagglutination which is not dispersed by saline is virtually pathognomonic for IMHA, usually caused by surface bound IgM antibodies or compliment fixation.
Coexisting thrombocytopaenia may also be immune-mediated (Evan’s syndrome) or result from disseminated intravascular coagulation.
Some cases of IMHA are nonregenerative due to the destruction of red cell precursors in the bone marrow.
The diagnosis of IMHA in cats is more problematic than in dogs. Spherocytosis and leucocytosis generally are not evident. Haemotrophic feline Mycoplasma spp., particularly Mycoplasma haemofelis, induce IMHA. Blood film examination is poorly sensitive; PCR assay is indicated in all cases of suspected feline IMHA. FIA related anaemia is strongly regenerative unless there is coexisting FeLV infection.
References: [[/en.wikivet.net/NationWide Laboratories|NationWide Laboratories]]
====Haematology====
====Haematology====