You might not be able to see a roarer from a mile away, but you sure can hear them. Horses with recurrent laryngeal neuropathy (RLN, often referred to as roarers due to the sound they make breathing) frequently require surgical intervention to both reduce the noise produced during exercise and to increase the amount of air they can take in while working.
Phil Cramp, BSc, BVM&S, MS, Dipl. ACVS, ECVS, MRCVS, a veterinarian at Rainbow Equine Hospital in Yorkshire, England, and Safia Barakzai, BVSc, MSc, Cert ES (Soft Tissue), DESTS, Dipl. ECVS, MRCVS, senior lecturer in Equine Surgery at the University of Edinburgh Royal (Dick) School of Veterinary Studies, recently reviewed the different surgical options currently available to treat horses with recurrent laryngeal neuropathy (RLN), their success rates, and morbidity (the rate of disease incidence after surgery).
In horses affected by RLN, the muscles that open and close the left side of the larynx as the horse breathes are paralyzed, causing the arytenoid cartilage (which closes over the trachea when a horse swallows) to droop into the left side of the airway. This effectively blocks the flow of air into the lungs. Clinical signs of disease include respiratory noise during exercise and reduced performance.
"The goals of surgery are to eliminate or reduce respiratory noise and/or improve athletic performance in affected individuals," Cramp said.
Choosing a Surgery
Cramp said that there are four factors to consider before selecting which surgical technique to use on a patient:
- The horse's intended use--Horses don't suffer ill effects from RLN unless they're carrying out an athletic activity, Cramp said. Affected pleasure horses, for example, might not require surgery to correct RLN. "Similarly, retiring an affected competition horse to a less athletic pursuit is a reasonable management option," he added.
- Disease severity--Horses with more severe RLN are often candidates for different surgical options than those with less severe disease, Cramp said. Thus, veterinarians typically assign a grade from I to IV (with IV being the most severe disease) to horses with RLN.
- Which clinical signs are present--"To some owners, respiratory nose is the principle issue whilst other owners wish to primarily address reduced athletic performance," Cramp said. Others may wish to treat both concurrently. Whilst there is a degree of overlap for most surgical procedures, some primarily seek to reduce respiratory noise and others aim to improve function."
- Costs and risks involved--Not surprisingly, more complex surgical options and those that require general anesthesia generally cost more financially and carry more risks when compared to less complex procedures.
Cramp reviewed each surgical option available to treat roarers, and noted the post-operative management, evidence of efficacy and possible complications for each procedure.
Ventriculectomy--This procedure involves removing the ventricle mucosa (the lining of the soft tissue structures of the larynx that are affected by RLN) to form a scar between the vocal fold, thyroid, and arytnoid cartilages, Cramp said. The scar tissue is believed to reduce the severity of vocal fold collapse into the airway and also reduce upper airway noise "by reducing turbulent airflow over the ventricle."
Veterinarians can perform ventriculectomies in standing sedated horses or those under general anesthesia. Post-surgery, horses require at least three weeks rest before returning to work, he added.
Cramp noted, "Recent experimental data ... suggest that bilateral ventriculectomy significantly reduces airway noise in horses with (severe) RLN, but not as effectively as bilateral ventriculocordectomy." (More on that procedure in a moment.)
Cramp said that complications associated with ventriculectomy are rare but can include mucocele (small, fluid-filled sacs) formation on the laryngeal wall and incision complications.
Ventriculocordectomy--This procedure is essentially a ventriculoectomy in addition to vocal cord removal, which is mainly used to treat respiratory noise caused by vocal cord collapse, Cramp said. This creates a smoother laryngeal contour, which should reduce respiratory noise, he said.
Veterinarians can perform ventroculocordectomies in standing sedated horses, under general anesthesia, or using a transendoscopic laser-assisted technique, Cramp said. Horses require four to six weeks rest before being reevaluated via an endoscope. "Some cases have residual inflammation at that stage and should be given a little extra rest time," he said.
"Experimental data has suggested that a longer time period (two to three months) may be required before the maximal effects are achieved in terms of reduction of respiratory noise and obstruction," he cautioned.
Cramp said experimental data has shown this procedure can significantly reduce upper airway sounds and obstructions 90 days post-surgery, and clinical cases have also shown a good success rate.
Complications associated with ventriculocordectomies are relatively rare, Cramp said, but include:
- Prolonged incision healing time;
- Laryngeal swelling necessitating tracheal intubation;
- Laryngeal swelling, granuloma formation, and arytnoid chondrosis (an uncommon acquired condition of the horse's larynx that leads to airway obstruction), mainly noticed with the laser-assisted technique; and
- Latent thermal damage when the laser is used.
Laryngoplasty--Often referred to as tieback surgery, this procedure involves placing one to two sutures in the left arytenoid cartilage to abduct and hold it out of the airway. Some owners find this an attractive option, due to its relatively short rehabilitation period, Cramp noted. "Post-operative care consists of stall rest for four weeks with hand walking only, then two weeks of small paddock turnout or light walking exercise," he said. "After six weeks, training can be resumed."
One study showed that laryngoplasty was effective in reducing upper airway noise by 30 days post-surgery, however the procedure was not as effective at minimizing noise as a ventriculocordectomy. Cramp also noted the horse's intended use is important to consider when measuring a procedure's success rate.
"Nonperformance horses that have submaximal exercising oxygen requirements are generally reported to enjoy high success rates of 70-92% after laryngoplasty," he said. "In comparison, laryngoplasty performed in racehorses is reported to have a lower rate of success (38-59%)."
Cramp also relayed that there are several complications known to accompany laryngoplasty:
- Coughing--Immediate post-operative coughing is reported in roughly 43% of patients, while chronic coughing is reported in about 14% of horses;
- Arytnoid abduction loss--This type of surgical failure (when the sutures fail or pull through the cartilage) is observed in 2 to 15% of affected horses in the immediate post-operative period. "The more insidious loss of abduction reported over the weeks and months following surgery that occurs in the majority of cases is problematic and difficult to prevent," Cramp said;
- Wound infection--The reported incidence of wounds at the incision site is between 0.5 and 6%, he said;
- Continued respiratory noise and/or poor performance--"Three recent studies reporting results of exercising endoscopy in horses that have undergone laryngoplasy have all reported that although arytnoid instability does occur in some cases, there is an alarmingly high incidence (48-59%) of dynamic laryngeal or pharyngeal collapse that is not arytnoid cartilage collapse," he said. Thus, it's important to examine the horse for another problem before concluding that the surgical procedure has failed; and
- Arytenoid chondritis--This condition, which refers to inflammation of the arytenoid cartilage, is reported in 1% of cases. However, Cramp added that "more recent studies with longer term follow-up of cases suggest that the prevalence ... may in fact be higher at 8% to 9%."
Arytenoidectomy--This procedure--the removal of all or a portion of the arytenoid cartilage on one side of the throat--requires general anesthesia, and often times veterinarians place a tracheostomy tube to assist breathing that is removed after 24 to 48 hours, Cramp said.
After surgery, veterinarians generally administer broad-spectrum antibiotics for three to five days in addition to anti-inflammatory medications for seven to 10 days, he said. Stall rest is typically prescribed for four to six weeks, he noted, followed by several weeks of walking. Cramp estimates an average recovery to take eight to 10 weeks.
"Recent studies comparing arytenoidectomy to laryngoplasy have found that in racehorses, laryngoplasty may be more successful ... both in terms of airway ventilation at maximal exercise and in racing performance parameters," Cramp said. "However, due to the high complication rate associated with laryngoplasty, more racehorses returned to racing after arytenoidectomy than after laryngoplasty."
Cramp said that intralaryngeal granulation tissue formation is common after arytenoidectomies. Other potential complications include dysphagia and chronic cough, however he noted that two recent studies did not identify in a total of 103 horses evaluated.
"No dynamic studies have been performed evaluating clinical cases in the long term after arytenoidectomy, however, our experience is that horses often exhibit collapse of unsupported soft tissue structures, most commonly the left aryepiglottic fold," he added.
Laryngeal reinnervation--This procedure involves transferring part(s) of a normal, innervated (supplied with nerves) muscle, or a nerve, into the non-functioning or poorly functioning cricoarytenoideus dorsalis (CAD) muscle of the larynx. Although the reinnervated CAD muscle doesn't function as well as a normal CAD muscle would, the results can be quite good during exercise.
Cramp said that while laryngeal reinnervations have fewer complications than some other surgical techniques, the procedure's long recovery time (up to 8-12 months for reinnervation to be complete in some horses) precludes its use in many candidates.
There are a few different types of laryngeal reinnervation equine surgeons can choose from including a neuromuscular pedicle graft (the common choice which uses a piece of the horse's omohyoideus muscle) and a programmed stimulator implant (which is used much less commonly as the current device is still having technical kinks worked out).
In summary, Cramp said, "Management of these cases and selection of the appropriate surgical technique should be based on the anticipated use of the horse, the owner/trainer expectations, and the risk of the procedure to the horse compared with the possible gain."
He noted that he believes the future of surgical roaring management lies in reinnervation techniques that are reasonably priced with "a reasonable timeframe to return to work."
The study, "Surgical management of recurrent laryngeal neuropathy," appeared in June 2012 in Equine Veterinary Education. The abstract is available online.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.