Polioencephalomalacia
Encyclopedia
Polioencephalomalacia literally means softening of the cerebrocortical grey matter
distributed in a laminar (layered) pattern. It is also called laminar cortical necrosis or cortical necrosis. PEM is a sporadic disease of unknown cause occurring in cattle
, sheep and goat
s. PEM is most commonly seen in cattle at 6–18 months of age when fed concentrate rations. Sheep are usually affected at 2–7 months of age.
The lesion is associated with thiamine
deficiency or a disturbance in thiamine metabolism. Ruminants are supplied with thiamine by synthetic activity of ruminal
bacteria
. PEM most commonly develops in cattle fed carbohydrate
-rich and roughage-poor rations, which leads to subclinical lactic acidosis
, and hence an alteration in ruminal microflora. Other mechanisms for disturbances in thiamine deficiency include:
- Destruction of thiamine within the gastrointestinal tract (for example by thiaminase
s in bracken fern)
- Inactivation of thiamine by excess sulfate
s or sulfide
s or elemental sulfur
- Production of inactive thiamine analogues
- Decreased thiamine absorption
- Increased faecal excretion of thiamine
Infection with Trypanosoma congolense can also cause focal PEM in the final stages of disease, likely due to ischemia from accumulation of parasites in the terminal capillaries of the brain.
Clinical signs of PEM are variable depending on the area of the cerebral cortex affected and may include head pressing, dullness, opisthotonos, central blindness
, anorexia, muscle tremors, teeth grinding, trismus, salivation, drooling, convulsion
s, nystagmus, clonic convulsions, and recumbency. Early administration of thiamine may be curative, but if the lesion is more advanced, then surviving animals may remain partially blind and mentally dull.
Grey matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil , glial cells and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts...
distributed in a laminar (layered) pattern. It is also called laminar cortical necrosis or cortical necrosis. PEM is a sporadic disease of unknown cause occurring in cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
, sheep and goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
s. PEM is most commonly seen in cattle at 6–18 months of age when fed concentrate rations. Sheep are usually affected at 2–7 months of age.
The lesion is associated with thiamine
Thiamine
Thiamine or thiamin or vitamin B1 , named as the "thio-vitamine" is a water-soluble vitamin of the B complex. First named aneurin for the detrimental neurological effects if not present in the diet, it was eventually assigned the generic descriptor name vitamin B1. Its phosphate derivatives are...
deficiency or a disturbance in thiamine metabolism. Ruminants are supplied with thiamine by synthetic activity of ruminal
Rumen
The rumen, also known as a paunch, forms the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. It serves as the primary site for microbial fermentation of ingested feed...
bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. PEM most commonly develops in cattle fed carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
-rich and roughage-poor rations, which leads to subclinical lactic acidosis
Lactic acidosis
Lactic acidosis is a physiological condition characterized by low pH in body tissues and blood accompanied by the buildup of lactate especially D-lactate, and is considered a distinct form of metabolic acidosis. The condition typically occurs when cells receive too little oxygen , for example...
, and hence an alteration in ruminal microflora. Other mechanisms for disturbances in thiamine deficiency include:
- Destruction of thiamine within the gastrointestinal tract (for example by thiaminase
Thiaminase
Thiaminase is an enzyme that metabolizes or breaks down thiamine into two molecular parts.The old name was "Aneurinase".There are two types: -Sources:Source include:* Bracken , Nardoo and other plants.* Some fish including carp and goldfish....
s in bracken fern)
- Inactivation of thiamine by excess sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
s or sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
s or elemental sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
- Production of inactive thiamine analogues
- Decreased thiamine absorption
- Increased faecal excretion of thiamine
Infection with Trypanosoma congolense can also cause focal PEM in the final stages of disease, likely due to ischemia from accumulation of parasites in the terminal capillaries of the brain.
Clinical signs of PEM are variable depending on the area of the cerebral cortex affected and may include head pressing, dullness, opisthotonos, central blindness
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
, anorexia, muscle tremors, teeth grinding, trismus, salivation, drooling, convulsion
Convulsion
A convulsion is a medical condition where body muscles contract and relax rapidly and repeatedly, resulting in an uncontrolled shaking of the body. Because a convulsion is often a symptom of an epileptic seizure, the term convulsion is sometimes used as a synonym for seizure...
s, nystagmus, clonic convulsions, and recumbency. Early administration of thiamine may be curative, but if the lesion is more advanced, then surviving animals may remain partially blind and mentally dull.
External links
- Polioencephalomalacia: Disease Caused by a Deficiency of Thiamine at tvsp.org
- http://ag.ansc.purdue.edu/sheep/ansc442/Semprojs/2002/neurological/polio.htm
- http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/102000.htm