Role of transcranial magnetic stimulation in differentiating motor nervous tract disorders from other causes of recumbency in four horses and one donkey

Abstract

Transcranial magnetic stimulation and measurement of the magnetic motor-evoked potentials (MMEPs) in the thoracic and pelvic limbs of four recumbent horses and one recumbent donkey were used to assess the integrity of the descending motor pathways, in order to confirm or exclude a descending motor tract lesion as the cause of the recumbency. In two of the animals abnormal MMEPs were recorded; in one of the horses a lesion along the cervical spinal cord due to a fracture of the fifth cervical vertebra was diagnosed and confirmed by radiography and postmortem examination; in another horse, damage to the peripheral nerves of the left forelimb was diagnosed and confirmed postmortem when a large abscess was found to have been compressing the peripheral nerves at the level of the last cervical vertebra. In the three other animals, normal MMEPs were recorded, and laminitis, rhabdomyolysis and physitis were diagnosed as the causes of the recumbency.

Central Nervous System Trauma

“…This method has recently been validated and used to distinguish motor tract disorders from other causes of recumbency in clinical cases. [76][77][78] …”

Accuracy of transcranial magnetic stimulation and a Bayesian latent class model for diagnosis of spinal cord dysfunction in horses

“…Transcranial magnetic stimulation (TMS) with recording of magnetic motor evoked potentials (MMEP) is a promising additional test for diagnosis of spinal cord dysfunctions in horses . A magnetic 70 mm coil is placed on the head of the horse, at the level of the brain, to perform a magnetic stimulation.…”

“…In horses, the mean latency time of 4 MMEP is used, instead of the minimal latency time which is used in humans. In normal horses, the mean latency time is short and has a low SD whereas in horses with spinal cord disease, latency time is more variable and clearly prolonged . A recent study that compared TMS with histopathology showed that for diagnosis of spinal cord dysfunction, the optimal cutoff values for latency time were 22 ms in the thoracic and 43 ms in the pelvic limbs .…”

The Use of Magnetic Resonance Imaging in Evaluating Horses With Spinal Ataxia

“…Electrodiagnostic testing may be a more sensitive indicator of neurologic dysfunction and aid in the neuroanatomic localization of the lesion. It has been evaluated in normal, ataxic, and recumbent horses . Electromyography is useful in differentiating between lower motor neuron disease and myopathies but does not provide information on the upper motor neurons and therefore it is not useful in the evaluation of cervical spinal cord disease .…”

“…When used to evaluate horses with cervical spinal cord disease, transcranial magnetic nerve stimulation was abnormal in all affected horses compared to the control population . It has also been used in recumbent horses to differentiate between neurologic and musculoskeletal causes of recumbency …”