Neurology

TMS

 

TMT is a non-invasive, objective, painless and sensitive neurological test that is performed on the standing, sedated horse. TMS in the horse is used for objective assessment of motor function, i.e. assessment of the motor tracts in the spinal cord. Both in human and animals with spinal cord lesions, magnetic stimulation of the brain is proven to be a valuable diagnostic tool for detection of lesions along the spinal cord. A magnetic stimulus (painless!!) is given, through the skull, to the cerebral motor cortex and subsequently electrical activity will pass through the motor tracts in the spinal cord and elicit a response in the musculature of the horse. This response is measured in the forelimbs in the extensor carpi radials muscle and in the hind limbs in the extensor carpi radialis muscle with electromyography. These electromyographic responses (MMEP’s, magnetic motor evoked potentials) are measured: the onset latency and the amplitude are determined. In horses suffering from spinal cord lesions the MMEP’s will demonstrate several typical abnormal features (even in mild spinal cord lesions): prolonged and variable latency, low amplitude and frequently polyphasic waveforms (Nollet, 2002). MMEP’s are always recorded in all 4 limbs. Recordings of the forelimbs and hind limbs are compared and the recordings of the left and right are compared to respectively distinct cervical spinal cord lesions from lesions located ofter the 2nd thoracic vertebra and to detect asymmetrical lesions. In Europe spinal ataxia is mostly caused by lesions in the cervical part of the spinal cord and most cases these lesions are the result of cervical vertebral malformation (CVM) or the so called ‚Wobbler’ syndrome. Other possibilities are infectious disease (EHV), trauma, fractures, tumors. When the lesion is located in the cervical spinal cord, radiography is performed. If the lesion is located caudal of Th2, final diagnosis is more difficult to obtain in the horse. Scintigraphy, radiography of thoracic and lumbar vertebra and rectal ultrasound are indicated.