Equine laryngeal hemiplegia. Part IV. Muscle pathology.

The research paper focuses on the existence of neurogenic muscle pathology in horses affected by laryngeal hemiplegia and also suggests that this condition may be a distal axonopathy. The amount of damage to the muscles is linked to the extent of damage in the recurrent laryngeal nerve.

Understanding Laryngeal Hemiplegia and Neurogenic Muscle Pathology

• The research aimed to understand the muscle pathology in horses affected by laryngeal hemiplegia, a condition characterized by paralysis of one side of the larynx due to damage to the recurrent laryngeal nerves.
• Neurogenic muscle pathology refers to muscle changes caused by nerve damage. This study confirmed its existence in intrinsic laryngeal muscles, which are the muscles inside the larynx directly controlled by the recurrent laryngeal nerves.

Findings Related to Polynenropathy

• An interesting observation was that three out of four horses with laryngeal hemiplegia also had neurogenic muscle changes in a hindlimb muscle, the extensor digitorum longus. This suggests the presence of a polynenropathy, a condition where multiple peripheral nerves throughout the body are simultaneously damaged.
• This condition is usually seen in the long peripheral nerves and supports the classification of laryngeal hemiplegia as a distal axonopathy, a disorder primarily caused by damage to the nerve fiber’s end region.

Correlation of Muscle Pathology and Nerve Damage

• The study also found a strong correlation between the degree of muscle pathology and the extent of the damage in the recurrent laryngeal nerves. Essentially, the more severe the nerve damage, the greater the muscle pathology.
• These findings indicate that the muscle damage seen in clinically affected horses is a reflection of the nerve damage present in the distal end of the recurrent laryngeal nerve.

Ongoing Pathological Processes

• The research highlighted the variable pathological changes found in the proximal levels of the recurrent laryngeal nerves, as this likely reflects an ongoing pathological process affecting the nerve fibers.
• Furthermore, the fact that there are asymptomatic horses is a significant finding. The earliest involvement of an adductor muscle (cricoarytenoideus lateralis) and changes in the right intrinsic laryngeal muscles further echo the findings of previous studies on the topic.