A review of the use of electromyography in equine neurological diseases

Transcranial Magnetic Stimulation and Transcranial Electrical Stimulation in Horses

Depending on the localization of the lesion, spinal cord ataxia is the most common type of ataxia in horses. Most prevalent diagnoses include cervical vertebral stenotic myelopathy (CVSM), equine protozoal myeloencephalitis (EPM), trauma and equine degenerative myeloencephalopathy (EDM). Other causes of ataxia and weakness are associated with infectious causes, trauma and neoplasia. A neurologic examination is indispensable to identify the type of ataxia. In addition, clinical neurophysiology offers tools to locate functional abnormalities in the central and peripheral nervous system. Clinical EMG assessment looks at the lower motoneuron function (LMN) and is used to differentiate between neuropathy in peripheral nerves, which belong to LMNs and myopathy. As LMNs reside in the spinal cord, it is possible to grossly localize lesions in the myelum by muscle examination. Transcranial (tc) stimulation techniques are gaining importance in all areas of medicine to assess the motor function of the spinal cord along the motor tracts to the LMNs. Applications in diagnostics, intraoperative neurophysiological monitoring (IONM), and evaluation of effects of treatment are still evolving in human medicine and offer new challenges in equine medicine. Tc stimulation techniques comprise transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES). TMS was first applied in horses in 1996 by Mayhew and colleagues and followed by TES. The methods are exchangeable for clinical diagnostic assessment but show a few differences. An outline is given on the principles, current clinical diagnostic applications and challenging possibilities of muscle evoked potentials (MEP) from transcranial stimulation in horses.

The potential and limitations of quantitative electromyography in equine medicine

This review discusses the scope of using (quantitative) electromyography (EMG) in diagnosing myopathies and neuropathies in equine patients. In human medicine, many EMG methods are available for the diagnosis, pathophysiological description and evaluation, monitoring, or rehabilitation of patients, and some of these techniques have also been applied to horses. EMG results are usually combined with other neurophysiological data, ultrasound, histochemistry, biochemistry of muscle biopsies, and clinical signs in order to provide a complete picture of the condition and its clinical course. EMG technology is commonly used in human medicine and has been subject to constant development and refinement since its introduction in 1929, but the usefulness of the technique in equine medicine is not yet widely acknowledged. The possibilities and limitations of some EMG applications for equine use are discussed.

Miscellaneous neurologic or neuromuscular disorders in horses

NMD is an important cause of morbidity in horses. Signs of dysfunction could be variable depending on the specific area affected. NM disease can go unrecognized if a thorough evaluation is not performed in diseased horses. Electrodiagnostic testing is an area that has the potential to document and improve our understanding of NM disease yet is uncommonly performed. Keeping an open and observant mind will enhance our ability to search and find answers.