According to Belgian researcher Heidi Nollet, DVM, PhD, and colleagues from the Department of Large Animal Internal Medicine, University of Gent, transcranial magnetic stimulation of a specific region of the brain called the motor cortex can be a powerful tool to help differentiate between a subtle lameness due to a musculoskeletal problem and a neurologic process.

This is achieved by magnetically stimulating the motor cortex, then measuring the response of such stimulation in peripheral muscles (including the extensor carpi radialis and the tibialis cranialis–large muscles of the fore- and hindlimbs, respectively) to assess the integrity of the motor pathways of the spinal cord. Abnormalities in the muscles’ response to motor cortex stimulation suggest an underlying neurologic condition rather than musculoskeletal issue.

Researchers performed this technique on 20 horses with either mild signs of incoordination or no distinct orthopaedic problems (i.e., as part of a pre-purchase examination). In all examined horses, no obvious distinction between a neurologic or orthopedic problem could be made based on standard examination procedures.

Twelve of the 20 subjects (60%) had abnormal muscular responses to the magnetic stimulation of the brain. Nollet and colleagues therefore concluded that transcranial magnetic stimulation can help practitioners differentiate between the origin of the gait abnormality in subtle cases where subjective clinical evaluation is inconclusive