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MRI used to diagnose cerebellar abiotrophy

stock-grass-The use of magnetic resonance imaging may help support a diagnosis of cerebellar abiotrophy, recent research suggests.

Cerebellar abiotrophy is a rare disease of Arabian and part-bred Arabian horses. It is believed to be due to an inherited abnormality that results in degeneration of Purkinje nerve cells in the cerebellum – thet part of the brain that controls fine movement.

Affected animals show signs of head tremor, jerky head movements and a lack of a menace response. Most affected animals are born normal, but usually develop signs by six months of age.

A definitive diagnosis is made on post mortem examination by identifying the characteristic signs on microscopic examination of the cerebellum.

There is no treatment. Earlier diagnosis would allow euthanasia to be carried out promptly rather than engaging in fruitless treatment attempts.

Recently, a single nucleotide polymorphism has been identified in the TOE1 gene which is associated with the disease in Arabian horses. A test has been developed which can be used to identify affected foals.

The latest issue of Equine Science Update  reports that another approach which has been studied recently is to examine the shape of the cerebellum using magnetic resonance imaging.

Research carried out at the University of Veterinary Medicine Hannover compared five affected foals with control images of 15 unaffected horses.

Jessika Cavalleri, Julia Metzger and colleagues conducted a study to assess the value of magnetic resonance imaging and morphometry (taking measurements from the scans) and genetic testing in supporting a diagnosis of the disease.

Measurements were taken from the mid-sagittal T2 weighted image of the brain. Of particular interest was the size of the cerebellum in relation to the rest of the brain and in relation to the space surrounding the cerebellum which is filled with cerebrospinal fluid (CSF).

All cases tested positive for the genetic test for the disease (that is, had the TOE1 genotype A/A).

The researchers found that, compared to normal horses, in affected horses the cerebellum was smaller relative to the brain as a whole, and the CSF space was bigger. Using a cut off value of 11 percent for relative cerebellar CSF space, they would differentiate between affected and controls, with 100 percent sensitivity and 93.3 percent specificity.

They warn that, because the study only involved a few affected animals, the data should be interpreted with care.

The results may have been influenced by the populations selected. Affected animals were Arabian or part-Arabian aged from 2 to 36 months. The 15 unaffected controls were mostly Warmblood (with one Arabian), ranging in age from 6 months to 10 years.

The researchers suggest further work to confirm their findings should involve more horses at different stages of the disease and normal Arabian horses.

They conclude that morphometric imaging and genetic analysis could help to support a diagnosis of the disease in live animals.

Morphometric magnetic resonance imaging and genetic testing in cerebellar abiotrophy in Arabian horses.
Cavalleri JMV, Metkger J, Lampe V, Stuckenschneider K, Tipold A, Beineke A, Becker K, Distl O, Feige K.
BMC Veterinary Research (2013) 9, 105
http://www.biomedcentral.com/1746-6148/9/105

Equine Science Update

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