Retrospective study of neurological signs and management of seven English horses with temporohyoid osteoarthropathy

Partial ceratohyoidectomy as surgical treatment for horses with temporohyoid osteoarthropathy: 10 cases (2010-2021)

OBJECTIVE

To describe outcomes of horses with temporohyoid osteoarthropathy (THO) treated with partial ceratohyoidectomy.

ANIMALS

10 client-owned horses.

PROCEDURES

Medical records from 2 institutions were examined for records of horses with THO treated with partial ceratohyoidectomy between 2010 and 2021. History, signalment, clinical signs, diagnostics, medications, and surgery-related details were recorded. Horses with a minimum of 6 months follow-up were recruited for neurologic and imaging examinations in the hospital or field where radiography of the basihyoid-ceratohyoid articulation were performed along with CT, when available.

RESULTS

10 horses with THO were included (9 unilateral; 1 bilateral). Nine planned partial ceratohyoidectomies were performed in 8 horses, whereas 2 horses had preoperatively planned complete ceratohyoidectomies transitioned to partial ceratohyoidectomies during surgery due to intraoperative complications. Postoperative complications occurred mostly in transitioned surgeries (obstructed airway, tongue mobility issues, and incisional hemorrhage), whereas only 1 horse with a planned ceratohyoidectomy had postoperative complication of rhabdomyolysis. All complications resolved before hospital discharge. Neurologic signs improved in all 10 horses, with 2 showing complete resolution. Nine horses were available for radiographic follow-up, 6 of which also had head CT scans. A space between the ceratohyoid and basihyoid bones was measurable on radiography in all 9 horses, and was confirmed on CT. Three horses demonstrated proliferation of either ceratohyoid or basihyoid bones. The 9 horses with unilateral disease returned to previous work, and the horse with bilateral disease was retired.

CLINICAL RELEVANCE

Partial ceratohyoidectomy is a surgical option for treatment of THO that provides similar clinical outcomes to published reports on ceratohyoidectomy.

Associations between styloid process sheath CT sizes and age, body weight, and breed in horses

The styloid process sheath (SPS) is a part of the tympanic temporal bone and an incomplete bony sleeve surrounding the styloid process, tympanohyoid cartilage, and dorsal part of the stylohyoid bone. In horses undergoing head CT, we observed a range of SPS sizes and questioned whether differences were early features of temporohyoid osteoarthropathy (THO) or normal anatomic variations associated with age, body weight, sex, or breed. We hypothesized that SPS sizes were positively correlated with age and body weight, but not with sex or breed. Using a convenience population of horses that underwent head CT at our institution (2008-2017), regardless of THO status, we investigated these hypotheses in a retrospective cross-sectional study. The sample comprised 102 horses. The median SPS height was larger medially (4.3 mm) than laterally (2.4 mm) and the median width was 11.1 mm: no difference was detected between sides. Geldings had a significantly larger median SPS width (11.6 mm) than stallions (8.7 mm; P < 0.05) and mares (10.0 mm; P < 0.05). No association was detected between SPS sizes and body weight and breed. Univariate and multivariate analyses initially found significant associations between SPS heights and age. Secondary analyses performed following removal of outliers and horses <2-years old found similar but less pronounced results (annual increase in SPS heights decreased from 3.2-3.8% to 0.9-2.6%). Most associations were insignificant when investigated by age group, but the annual rate of increased size might be faster in older horses. Excessive SPS enlargement was theorized as an essential component of THO.

Symptoms and management of temporohyoid osteoarthropathy and its association with crib-biting behavior in 11 Japanese Thoroughbreds

There have been few reports about temporohyoid osteoarthropathy in Japanese horses. The aim of this study was to describe the symptoms and management of temporohyoid osteoarthropathy and to investigate its association with crib-biting behavior, which is commonly observed in Japanese horses. The data concerning case details, signs, diagnosis procedures, treatment, and outcomes were collected retrospectively from the medical records of 11 Thoroughbreds with temporohyoid osteoarthropathy. The trainers and owners were asked whether the horses had displayed crib-biting behavior. Nine of the horses were diagnosed by guttural pouch endoscopy, and two were diagnosed by skull radiography. Eight horses were treated medically, of which three (37%) showed improvement; the other three horses underwent ceratohyoidectomy, with two (67%) showing improvement. Crib-biting behavior was observed in eight (73%) of the horses. A comparison of data regarding crib-biting behavior among 437 Thoroughbreds from six local riding schools indicated a significant association between temporohyoid osteoarthropathy and crib-biting behavior: the odds ratio for a horse with temporohyoid osteoarthropathy to exhibit crib-biting behavior compared with the general population was 12 (95% confidence interval, 3–45), and horses exhibiting crib-biting behavior were significantly more likely to have temporohyoid osteoarthropathy (P<0.001, Fisher’s exact test). This suggested that crib-biting behavior may be a risk factor for temporohyoid osteoarthropathy.

Neurologic Deficits Including Auditory Loss and Recovery of Function in Horses with Temporohyoid Osteoarthropathy

BACKGROUND

Auditory loss is a common deficit in horses with temporohyoid osteoarthropathy (THO), however, recovery of function is unknown.

HYPOTHESIS/OBJECTIVES

To investigate neurologic function with emphasis in audition in horses with THO after treatment. To describe anatomical alterations of the petrous temporal bone that might result in auditory loss.

ANIMALS

Twenty-four horses with a clinical diagnosis of THO.

METHODS

Prospective study. A brainstem auditory evoked response (BAER) study was done as part of the criteria for inclusion in horses with a clinical diagnosis of THO from the years of 2005 to 2014. Physical and neurologic status and BAER findings were recorded. Brainstem auditory evoked response variables were compared by using Wilcoxon sign test. Fisher's exact test was also used. Significance was set at P < 0.05.

RESULTS

The most common signs included auditory loss (100% of horses), vestibular and facial nerve dysfunction (83%), and exposure ulcerative keratitis (71%). Concurrent left laryngeal hemiparesis was observed in 61% of horses through endoscopy. Auditory dysfunction was bilateral in 50% of the cases (complete and partial), and unilateral affecting more commonly the right ear (R = 8, L = 4). Short- and long-term follow-up revealed persistent auditory loss in all horses based on abnormal response to sound, and further confirmed through a BAER in 8 horses.

CONCLUSIONS AND CLINICAL IMPORTANCE

Auditory dysfunction appears to be a permanent neurologic deficit in horses diagnosed with THO despite overall neurologic improvement.

Update on disorders and treatment of the guttural pouch

The most common disorders of the equine guttural pouches are empyema, tympany, mycosis, and temporohyoid osteoarthropathy. Diagnosis of these conditions is made primarily by imaging with endoscopy, radiographs, computed tomography, and/or MRI. Medical treatment with anti-inflammatories, antimicrobials, and/or antifungals may be successful in some cases, but many of these disorders necessitate surgical intervention. Direct surgical approaches to the guttural pouch are difficult because of their complex anatomy and relationship with important structures, thus precipitating a move toward minimally invasive procedures when possible.