Management and long-term outcome of partial glossectomy in 2 horses

Abstract

Records were reviewed for 2 horses with partial glossectomy, 1 traumatic and 1 elective. According to long-term follow-up by telephone, both horses had recovered well, experiencing only temporary difficulty while eating, and went on to be ridden successfully using mouth bits. Partial glossectomy, therefore, had a favorable prognosis in 2 performance horses.

The tongue serves as an organ of food prehension, mastication, grooming, deglutition, taste, and vocalization, and is suspected to play a role in upper airway stability (1–4). Some reported abnormalities of the tongue in the horse include traumatic injuries (1,5–10), glossitis (10,11), neoplasia (12–14), and tongue paralysis (15–20). Lacerations to the tongue of horses are common (6), usually involve the free portion of the tongue, and the majority are transverse in orientation (6,7). These lacerations can result from foreign objects, self-inflicted bites, or inappropriate use of bits (1,5–9). Clinical signs include oral hemorrhage, ptyalism, inappetence, anorexia, dysphagia, halitosis, pyrexia, and tongue protrusion from the mouth (7). Tongue injuries can be managed with primary closure, second intention healing or glossectomy depending on the severity, duration, and location of the injury (1,5–9).

This paper reports the use of partial glossectomy as a treatment for tongue paralysis, and reports the long-term outcome, especially with regards to performance when ridden with a bit, following traumatic and elective glossectomy. The authors are unaware of any other reports on the performance of horses under bridle after having a major portion of the apex of the tongue removed.

Case descriptions

Case 1

A 15-year-old, 526-kg, Quarter horse gelding, used for pleasure riding, was admitted with a history of complete traumatic amputation of the rostral portion of the tongue (12 cm). The owner noticed the horse was inappetent, had excess salivation, blood around the mouth and on the front legs, and the portion of the tongue was found. Oral examination revealed complete, transverse laceration of the tongue with loss of the rostral 1/3 of the tongue just rostral to the frenulum (i.e., tongue apex). The horse was administered ceftiofur and phenylbutazone and referred to the hospital due to not being able to eat and drink properly.

On admission, the gelding was tachycardic and mildly dehydrated. He was given Lactated Ringers solution (Hospira, Montreal, Quebec), 65 mL/kg body weight (BW) per day, IV, and continued on ceftiofur (Excenel; Pfizer Canada, Kirkland, Quebec), 1 g IV, q24h, for 4 d, phenylbutazone (Bute, Phenylbutazone 20%; Rafter Products, Calgary, Alberta), 2.2 to 4.4 mg/kg BW, IV, q24h for 2 d, and a tetanus toxoid vaccine (Tetanus Toxoid, Wyeth Animal Health, Guelph, Ontario), IM.

During the 7-day hospitalization period, soaked pelleted rations, soaked beet pulp, and grass hay were offered. For 2 d he was unable to masticate and swallow effectively, and only small amounts of feed were ingested. By day 3 he started to chew and swallow but dropped the majority of his feed. Mashes were at first more difficult to keep in his mouth, but required less chewing. On day 4 a nasogastric tube was passed and 8 L of senior pellet slurry was administered. On day 5, on oral examination the tongue appeared to be healing well by second intention. He continued to improve in his ability to eat and was discharged on day 7 with instructions to continue special feeding.

A phone interview was conducted with both the owner and trainer of the gelding 2.5 y following the injury. For 6 mo he was fed free choice grass hay and a large mash of senior feed, soaked beet pulp once daily, with powdered salt and minerals added because of his inability to lick salt/mineral blocks. Then he had free choice pasture grazing in the summer and free choice hay in the winter.

Weight loss was noticed initially, but he progressively regained his original weight. The owner feels maintaining a healthy weight is now more difficult, the horse eats more slowly, his lips and facial muscles are more developed and dynamic in movement, and he has developed the ability to protrude a small amount of the remaining portion of his tongue.

Riding with a halter resumed 5 months following the injury, and at 1 year a professional trainer started him in a hackamore and then transferred him to a bit with a wide, medium height port and loose shanks, designed to utilize the bars and roof of the horse’s mouth rather than the tongue. The trainer reported that the horse could move the bit with its tongue, so the stump of the tongue was able to get under or contact the bit’s mouthpiece. The horse was very responsive to a slow soft pressure on the reins, but compared to normal horses, he overreacted to more sudden firm pressure on the bit. The owner feels the horse has no abnormal behaviors in response to the bit, but because he is no longer able to lick saliva from his lips he wipes his muzzle on his front legs during work, rest, and eating. The horse has returned to a slightly higher level of work than prior to the injury.

Case 2

A 7-month old, weaned, 220-kg, Quarter horse filly was presented with a history of tongue protrusion from the left side of her mouth since birth (Figure 1). There was no evidence of trauma at birth (parturition not observed), the dam’s previous foals and ancestors were all normal, and all horses on the farm had been healthy during the pregnancy. As a foal the horse seemed to have some difficulty nursing; however, she appeared to develop normally. After weaning she was fed hay and grain, and had no difficulty eating. Just prior to presentation she had sustained a mild laceration to the tongue, likely due to biting it.

Figure 1.

Case 2, protrusion of the tongue from the left interdental space on presentation.

On examination, the filly was in good body condition and normal except that 6 cm of her tongue protruded at an angle from the left side of her mouth through the interdental space (Figure 1). The dorsal aspect of the protruding portion of the tongue had callous formation where it lay against the left premolars. It remained protruded, but could be retracted completely into the mouth during eating and when it was pulled. Tongue tone felt mildly to moderately decreased and the left side of the tongue appeared slightly atrophied.

No abnormalities were seen on radiographic examination of the head and hyoid area. On resting videoendoscopy of the upper airway there was a small amount of white material within the left guttural pouch which was collected for culture and sensitivity. Actinobacillus species, that was sensitive to all the antibiotics tested, was grown. A specific diagnosis was not made. A congenital generalized decreased muscle tone to the tongue, and atrophy of the left side of the tongue were suspected.

Surgical removal of the protruding portion of the tongue was recommended to protect the tongue from trauma on external objects or from freezing during the winter. The American Quarter Horse Association (AQHA) was contacted and granted permission for surgical treatment without affecting the horse’s registration or performance record.

Before surgery, the filly was given sodium penicillin (Penicillin G Sodium; Novopharm, Scarborough, Ontario), 22 000 IU/kg BW, IV, q6h, and phenylbutazone (Rafter Products), 2.2 to 4.4 mg/kg BW, IV, q24h, and the portion of the tongue protruding was marked with a blue marker and staples once the horse was anesthetized. She was anesthetized and positioned in right lateral recumbency. A local block with 2% lidocaine hydrochloride was performed at the base of the tongue, and a tourniquet was placed just cranial to the frenulum to control hemorrhage. The site selected for amputation was 7 cm caudal to the tip of the tongue, 3.5 cm rostral to the lingual frenulum, located 1.5 cm caudal to the protruding portion of tongue, and running transversely across the tongue. To allow optimal closure, the tongue tissue was incised at an angle such that a wedge of musculature was removed, leaving dorsal and ventral flaps that could be easily apposed without tension (5,6). The tissue flaps were reduced with 3 horizontal and 1 vertical mattress sutures using 1 polydioxanone (PDS II, Ethicon Canada, Markham, Ontario). Triangular wedges of tissue were removed on either side of the tongue to prevent “dog ear” formation at the ends of the opposed flaps. The edges of the flaps were apposed with 2 separate pieces of 0 PDS in a simple continuous suture pattern (Figure 2).

Figure 2.

Case 2, intra-operative view of the tongue showing the amputated portion and the sutured stump. Rostral to the marker line represents the portion of tongue that had protruded.

Immediately following recovery from anesthesia there was no tongue protruding from the filly’s mouth (Figure 3). The filly had some difficulty initially eating a mash of bran and senior pellets, but later that day was able to eat hay without any difficulty. She was discharged with instructions for administration of phenylbutazone (1 g PO, q24h for 3 days).

Figure 3.

Case 2, appearance of the tongue 2 hours after partial glossectomy.

Two weeks after surgery the filly was eating well and sutures were still in place. A telephone interview was conducted 3.5 y following surgery once the filly was in full work. The owner reported that the filly did not have trouble eating, had normal eating behavior, maintained a good body condition, and as a yearling was a champion halter horse. She was started under saddle at about 32 mo of age (2 y post surgery) using a snaffle bit with a jointed mouthpiece. The owner did not notice any abnormality with her accepting the bit, and for the past 18 mo she has been ridden 1.5 hours 5 times a week, in training as a working cow horse, without any abnormalities seen. The owner reports that about 2 cm of tongue are located under the bit’s mouthpiece.

Discussion

Traumatic glossectomy or glossectomy as a treatment for severely traumatized tongues (devitalized or with minimal attachment to the parent portion of tongue) in horses has been previously described (1,5–9). Based on a classification system for human glossectomies, and adopted for injuries in dogs (2), both glossectomies in this report are classified as “partial glossectomies,” which are defined as loss or amputation of part or all of the free tongue rostral to the frenulum. Elective glossectomy has not been described as a treatment for glossitis, neoplasia, or tongue paralysis in the horse (10–20), but has been used for such conditions in dogs (2). Partial glossectomy should be considered as a viable treatment option in horses, especially with conditions refractory to medical management. To the authors’ knowledge this is the first report of a partial glossectomy in the horse as a surgical treatment for persistent tongue paralysis or protrusion.

Potential causes of tongue protrusion or paralysis in the horse include abnormal behavior (21), congenital abnormality (15), botulism (16,19,20), abnormalities of or injury to the hypoglossal nerve or its origin (3,4,17,18,20,22), and equine protozoal myeloencephalitis (15). The muscles of the tongue, styloglossus, hyoglossus, and genioglossus, all receive their motor innervation from the hypoglossal nerve [cranial nerve XII (CN XII)] (3,4,18,22), which has a nucleus in the medulla of the hind brain (3,18). These muscles all play some role in retraction of the tongue but are also important for depression and protrusion of the tongue (3,4). The genioglossus muscle, which is important in tongue protrusion, is innervated by contralateral cortical fibers, whereas the other tongue muscles have bilateral cortical innervation (22). The clinical significance is that a unilateral cortical lesion may cause contralateral genioglossus muscle weakness and deviation of the protruded tongue away from the side of the lesion, whereas a CN XII injury causes ipsilateral genioglossus muscle weakness with the protruded tongue deviating to the side of the injured nerve (22). Because of different muscle actions and innervation, localization of brain or nerve injury can be very difficult.

The presence of tongue protrusion in case 2 since birth rules out a behavioral problem. A congenital problem with the tongue musculature or hypoglossal nerve or its cortical center, or an injury while foaling is possible but no other abnormalities were identified on clinical examination or radiographs, and the amputated portion was not sent for histological examination. The hypoglossal nerve passes close to the guttural pouch; however, the empyema seen at 7 mo of age was minimal and not likely present at birth. Equine protozoal myeloencephalits (EPM) can have transplacental transmission (15); however, this filly was born and raised in western Canada where Sarcocystis neurona infection has not been previously reported. Neospora hughesi has been reported to cause EPM in a horse that had not been outside of western Canada (23). Although the horse in case 2 was not tested for EPM, the likelihood of it being the cause of the tongue abnormality is very low considering the geographic location and the lack of other clinical signs later on in life. The cause of the tongue protrusion remains unknown; however, we suspect some abnormality in hypoglossal nerve innervation.

Complications following a partial glossectomy are possible but not usually significant. Although contamination is inevitable, infection is rare (2,5). Excessive swelling of the tongue and suture dehiscence are possible and their chances of occurring can be decreased with the use of antibiotics, non-steroidal anti-inflammatory drugs, oral antiseptic rinses, obliterating dead space with the use of tension relieving sutures, and feeding mashes after surgery (6,7). Tongue wounds heal well by second intention healing (5–7); however, primary closure and antibiotic therapy will likely hasten healing and improve functionality and cosmetics (1,5–8). Acid-base disturbances from excessive loss of saliva have been reported (1,2), but were not observed in these cases.

Most horses are able to eat and drink effectively following a partial glossectomy (1,5–8). They may initially have some difficulty, but quickly adapt as observed with both cases in this report. Dogs with more extensive glossectomies, subtotal or total, quickly learn how to eat (2). A study in humans revealed that the volume of food swallowed per second was significantly correlated to the area of tongue removed, and that deglutition remained within the normal range if less than 1/6 of the entire tongue was removed (23). The authors could not find any reports of the normal length of the horse’s tongue, which would likely vary depending on age, size, and breed. However, the horses in our study lost most of the apex (12 and 7 cm), the free portion of the tongue rostral to the frenulum; therefore, the authors believe that this is greater than 1/6 of the entire length of these horses’ tongues. The 2 horses both initially ingested their food more slowly; therefore, allowing access to food for a longer period of time is necessary in the initial post-operative period. As observed with our 2 cases, mashes or grain are more easily dropped initially; however, they are important in initial post-operative management as these foods are less abrasive, require less chewing, are likely easier to swallow, and have a more predictable nutritional value than hay. Hay may be well-tolerated but must be of high quality as more work is required during mastication. The horse in Case 2 adapted quickly and now maintains a healthy body condition on a typical diet. The horse in Case 1 had more difficulty eating immediately after surgery and subsequently had visible chewing abnormalities and difficulty retaining an ideal body condition on a normal horse ration. This may be related to the traumatic nature of the injury that pulled off the rostral portion of the tongue, and the possibility that some neurological damage occurred to the remaining tongue. This horse, in contrast to the horse in case 2, had a normal tongue prior to injury and therefore was not preconditioned to altered tongue function.

Tongue amputation to the level of the frenulum is well-tolerated with regard to eating (5,9), but there is no information regarding a horse’s athletic performance and acceptance of a bit. Both horses in our study went on to excellent performance with use of mouth bits. The trainer of the horse in case 1 used a bit with a wide, high port and loose shanks that would theoretically put less pressure on the tongue and utilize the bars and palate of the mouth more. The horse in Case 2 was untrained prior to glossectomy but subjectively responded normally to training, initially with a jointed ring bit snaffle which was followed by a D-ring snaffle bit. All bits put some pressure on the tongue (21) so a bit-less bridle, hackamore, or bosal may be an easy solution after a glossectomy; however, some disciplines require a horse to compete with a bit. Our report demonstrates that horses can perform well with a bit after a partial glossectomy but understanding the mechanics of bits, bridles, and accessories may be helpful to owners and veterinarians. Generally, horses are started with a snaffle bit (ringed bit with no shanks) that has a jointed mouthpiece and eventually are advanced into bits with a solid mouth piece, port (elevated portion of the mouthpiece), and shanks. These devices can exert pressure on a number of areas including: bars (mandibular interdental space), lips, tongue, hard palate, chin, nose, and poll (21), with the tongue and palate being the most sensitive (21). The tongue normally protects the bars from pressure as it sits higher, partially covers the bars, and absorbs some of the force (25,26). Snaffle bits have rings for attachment of the reins rather than a shank, and a pull puts pressure on the tongue, bars, and lip corners (21). A straight mouthpiece exerts more pressure on the tongue compared to a jointed mouthpiece, which bends over the tongue and places more pressure on the bars and lips (21). The diameter of the mouthpiece also plays a role in severity with narrow being more severe (21). Ported bits have less contact with the tongue but put pressure on the hard palate (21), and are generally reserved for horses more advanced in training. Shank bits give a mechanical advantage so that less force on the reins is required to exert a given pressure in the mouth (21).

Following a partial glossectomy the bit may be problematic if its mouthpiece irritates the tongue stump or gets under the tip of the tongue. However, if the bit’s mouthpiece is located rostral to the stump more pressure from the bit’s mouthpiece will be placed on the bars and lips. In both our cases the horses performed well with bits. The horse in Case 1 had some problems initially adjusting to the bit despite already being trained. This might be related to the stump being located caudal to the mouthpiece; however, since the horse was capable of moving the bit around it must have been able to get it under the mouthpiece due to the wide port. The horse in Case 2 accepted a bit normally, possibly because the tongue was long enough to extend under the mouthpiece. For an untrained horse started after a partial glossectomy, a snaffle bit with a jointed and larger diameter mouthpiece may be best to minimize pressure on the tongue and bars. For a trained horse after partial glossectomy, a bit with a wide low port with mobile shanks is likely optimal.

This report verifies both that horses can eat well after a partial glossectomy with removal of the tongue just rostral to the frenulum, and that they can return to a high level of performance while ridden with a bit. Partial glossectomy should be considered as a treatment option for any condition in which partial amputation of the tongue could be beneficial to the horse. CVJ