Common conditions
• LARYNGEAL HEMIPLEGIA
Laryngeal hemiplegia occurs as a result of paralysis of either one or both arytenoid cartilages with left-sided paralysis being most commonly encountered. Paralysis occurs due to loss of nerve fibres in the recurrent laryngeal nerve that supplies the cricoarytenoideus dorsalis muscle. This paralysis means that the muscle loses its ability to contract and move the arytenoid cartilage into an abducted (outward) position. This results in an asymmetric rima glottidis with the cartilage on the affected side ‘drooping down’.
Varying degrees of paralysis occur and these are graded on a scale of one to four. In most horses there is no obvious reason for the loss of nerve function, but genetic predisposition is likely.
Patients with laryngeal hemiplegia generally present with a history of an abnormal inspiratory noise — a whistle or roar, which is why a horse with laryngeal hemiplegia is often referred to as a roarer. They may also have a history of exercise intolerance. Occasionally, laryngeal hemiplegia is noted as an incidental finding when the horse is being examined for another reason.
Diagnosis is often suspected based on the presence of compatible clinical signs. Laryngeal palpation may reveal loss of cricoarytenoideus dorsalis muscle mass on the affected side, but an endoscopy is required to confirm the diagnosis. Resting endoscopy is generally performed in the first instance, followed up by exercise endoscopy if necessary.
If treatment is required, a number of surgical options are available, including a tie-back. Your vet will formulate the most appropriate treatment plan based on the horse, what he is used for, and the severity of the paralysis.
• LARYNGEAL PARALYSIS
Laryngeal paralysis may also occur as a result of toxicity (organophosphate and lead, to name but two), liver failure (hepatic encephalopathy), and central nervous system disease. The horse will often be in respiratory distress as his larynx is paralysed, forming a physical barrier to the movement of air into the lower respiratory tract. Such patients require emergency intervention in the form of a tracheostomy (the creation of an opening in the windpipe to allow air to bypass the paralysed larynx and enter the lungs). Prognosis is poor.
• ARYTENOID CHONDRITIS
Arytenoid chondritis is an inflammatory condition of the horse’s arytenoid cartilage that results in a spaceoccupying mass within the larynx. On endoscopy, the affected cartilage appears enlarged and a drainage tract, as well as granulation tissue, may be evident. Generally, only one arytenoid is affected.
The condition is believed to occur secondary to trauma or infection. Affected horses generally present with a history of an inspiratory noise with or without exercise intolerance, a cough, and/or difficulties in swallowing. They may also be in respiratory distress. Diagnosis is based on endoscopic visualisation of the larynx.
Treatment consists of antibiotics and anti-inflammatories, and a throat spray may also be formulated. In severe cases, or in cases where treatment is unsuccessful, surgery may be required.
• EPIGLOTTIC ENTRAPMENT
In simple terms, epiglottic entrapment occurs when a band of tissue becomes positioned over the epiglottis, resulting in ulcerative changes. Affected horses present with an abnormal respiratory noise and exercise intolerance. Coughing and nasal discharge are occasionally reported. As with most laryngeal conditions, diagnosis is based on endoscopy and treatment is surgical.
• SUBEPIGLOTTIC CYSTS
As the name suggests, subepiglottic cysts are located beneath the epiglottis. Cysts may be congenital, with affected patients presenting at a young age with a history of coughing, difficulty in swallowing, and sometimes food/fluid entering the respiratory tract. Cysts may also be seen in older horses in which the condition is considered acquired. These patients present with a respiratory noise, cough and difficulties in swallowing.
Diagnosis of subepiglottic cysts is based on endoscopic examination and surgery is needed to remove them.