The role of quantitative electromyography (EMG) in horses suspected of acute and chronic grass sickness.

This research explores the use of quantitative electromyography (EMG) to reveal previously undetectable motor neuron changes in horses suffering from equine grass sickness (EGS). The study found that all diagnosed horses showed EMG results indicating neuropathy of skeletal muscles, providing additional evidence that may assist in the differential diagnosis of EGS in symptoms similar to weight loss and colic.

Research objectives and methods

• The study aimed to identify minute changes in the lower motor neuron system in horses suffering from EGS using quantitative EMG. The research was conducted on living horses (ante mortem).
• Fourteen horses diagnosed with EGS in its various forms (acute, subacute or chronic) underwent quantitative EMG exams.
• Control data was utilized from healthy horses and horses with diagnosed lower motor neuron disease (LMND).
• 8 of the horses also had a post-mortem exam, and 7 of them had muscle biopsies of the lateral vastus muscle to undergo histopathology and morphometry.

Research findings

• The EMG revealed clinical electrophysiological evidence of neuropathy in twelve of the horses.
• Specific data related to the motor unit action potential (MUP) duration and amplitude, number of phases, and number of turns were calculated for different muscles, providing a base of comparison for future studies.
• No changes were identified in insertional activity duration, however pathological spontaneous activity was observed in all horses.
• All 8 horses that went through post-mortem examination showed EGS evident by degenerative changes in the autonomic ganglia along with minor degenerative changes of the spinal lower motor neurons.
• Out of 7 biopsied horses, four showed changes consistent with slight neurogenic atrophy.

Conclusion

• All horses suspected of EGS displayed evidence of a neuropathy of the skeletal muscles as shown by the EMG results.
• These findings combined with clinical symptoms can potentially assist in differential diagnosis in cases showing signs of weight loss and colic, commonly associated with neurogenic diseases in horses.