100


EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2022


risk of antibiotic-associated enterocolitis, the dose of penicillin was lowered to 22,000 iu/kg bwt i.v. q. 6 h. Due to progressive inappetence, the route of administration of the metronidazole was switched from per os to per rectum at a dose of 20 mg/kg q. 8 h (Steinman et al. 2000). Over the following 2 weeks of hospitalisation, the gelding slowly improved. The facial swelling decreased, the heart rate and rectal temperature normalised and the appetite improved. The gelding underwent CT examination every 4–5 days to


monitor the progress of the emphysema. The studies showed gradual improvement. The fasciotomies were allowed to close by second intention. Antibiotic therapy was transitioned from intravenous penicillin/gentamicin to Trimethoprim- sulfamethoxazole (30 mg/kg bwt q. 12 h, per os) on Day 21, due to satisfactory clinical and imaging improvement. At 30 days post-presentation, the facial swelling was considered to have resolved. A complete blood count performed at this time showed no abnormalities. The gelding was discharged at 25 days post-presentation for further care at the farm, with instructions to clean the healing fasciotomy sites and to return for a repeat oral examination and head CT in 30 days.


Follow-up


The gelding presented for follow-up at 30 days. At this time, the fasciotomy sites were well-healed and the soft tissue swelling of the head had resolved (Fig 4). There was no history of recurrence of the right-sided nasal discharge. Oral examination was unchanged from the previous examination. Follow-up standing CT revealed resolution of the soft tissue thickening and no evidence of emphysema (Fig 5). There was soft tissue attenuating signal consistent with inspissated purulent debris in the right ventral conchal sinus. The previously described dental abnormalities were unchanged.


At this time, resting upper airway endoscopy was


performed and was unremarkable. Treatment of the chronic sinusitis was discussed with the owner, who expressed a reluctance to perform sinoscopy for cosmetic reasons. Trans- endoscopic fenestration of the right ventral concha with a contact diode laser via the nasal passage was performed following local desensitisation with 2% mepivacaine. Thick purulent material was flushed from the sinus via a chambers catheter inserted into the opening. The gelding was discharged with instructions to monitor for recurrence of the nasal discharge.


Discussion


In this report, myonecrosis of the soft tissues of the head with concurrent sinusitis was caused by Prevotella intermedia and Peptostreptococcus asaccharolyticus. How the bacteria were able to enter and establish infection in these tissues remains unclear, since no penetrating wound or foreign body was identified and the case resolved without removal of any tooth. Due to their ability to express potent virulence factors such as endotoxin and collagenases, Prevotella species are frequently identified in cases of severe periodontitis in man and in veterinary species (Borsanelli et al. 2017). Kennedy et al. (2016) assessed the oral microbiome of horses with and without periodontal disease and found that affected horses had a different, more diverse microbiome, with Prevotella species being the most prevalent. Bailey and Love (1991) isolated bacteria from the pharyngeal tonsillar surface of horses with and without lower respiratory tract or oral bacterial infections and identified Peptostreptococcus species in both normal and diseased horses, suggesting that this species is an opportunistic pathogen of the pharynx. The horse described in this report had infundibular caries of 109 and 110 and though the emphysema and other clinical signs resolved without tooth removal, it is possible that the compromised oral health of the horse contributed to the pathogenesis of the myonecrosis, perhaps following a small penetrating wound of the oral mucosa. The affected teeth were not removed as there was concern that standing removal of the teeth would require performance of a maxillary nerve block, which given the location of the myonecrosis was contraindicated. At presentation, the differential diagnoses were


Fig 4: Side photograph of the gelding at the 30 day recheck showing resolution of the soft tissue swelling and good healing of the fasciotomies. The right-sided nasal discharge was also resolved at this time.


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periodontal disease, neoplasia, mandibular fracture or abscess, sialadenitis or sialolithiasis, Streptococcus equi equi infection, snake bite and myositis. The initial CT examination was most consistent with that of anaerobic myositis as there was extensive emphysema within markedly swollen soft tissues with gas bubbles tracking along the fascial planes. No discrete abscess or neoplasm could be identified and, coupled with the acute presentation, these were considered less likely. The gas identified on CT did not appear to extend into or originate from the parotid gland. The tooth roots, although not normal, did not appear to be abscessed. The upper airway endoscopy performed at admission determined the guttural pouches were free of empyema. No external wound or puncture marks were identified on the skin, thus following the advanced imaging the diagnosis of myonecrosis, presumed to be due to Clostridial species, was most likely (Peek et al. 2003). Most cases of Clostridial myonecrosis occur in the cervical or gluteal musculature, a direct consequence of the


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