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

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.