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

This retrospective study summarises the case details, presenting signs, management and outcome in cases of temporohyoid osteoarthropathy (THO) and describes the findings of diagnostic imaging modalities. The condition appears to be relatively rare in Europe and the objective of this study is to make clinicians aware that THO can have a range of various neurological and clinical presentations. The records of 2 referral equine practices in England were reviewed and 7 horses with THO diagnosed on guttural pouch endoscopy indentified. The clinical and neurological signs, diagnostic procedures, treatment and outcomes were reviewed. Although small, this group is the largest case series of THO from Europe. One horse was a yearling, whereas THO is generally considered usually to affect middle aged and older horses. Computed tomography was used to confirm the diagnosis and demonstrated stylohyoid bone fractures in 2 cases while there was mild increased radionuclide uptake in one of 2 cases undergoing nuclear scintigraphy. Treatment is still controversial, although ceratohyoidectomy led to complete resolution of signs in 2 of 5 cases thus treated and improvement in the other 3. One horse with mild signs treated with antimicrobials and nonsteroidal anti‐inflammatory drugs made a full recovery while another, presented with head shaking and managed with a phased exercise programme, improved but did not resolve completely.     

Temporohyoid osteoarthropathy and unilateral facial nerve paralysis in a horse

A 13-year-old broodmare was referred for weight loss and left facial nerve paralysis. Bilateral temporohyoid osteoarthropathy was diagnosed based on proliferation of the temporohyoid joints and stylohyoid bones on radiographs and guttural pouch endoscopy. The left side was more severely affected. Treatment resulted in little or no improvement.     

Shear mouth secondary to temporohyoid osteoarthropathy

Temporohyoid osteoarthropathy (THO) is a progressive disease of unknown aetiology that can result in pain during normal movement of the tongue and larynx during mastication and deglutition. Shear mouth is a rare, poorly described condition, which may be associated with painful dental disease. This report describes a case of shear mouth attributable to THO. The THO was surgically treated by undertaking a left-sided ceratohyoidectomy (CHO) and the shear mouth resolved over the course of 18 months.     

Bilateral ceratohyoidectomy for the resolution of clinical signs associated with temporohyoid osteoarthropathy

Temporohyoid osteoarthropathy (THO) is a progressive bilateral disease of unknown aetiology that most commonly affects adult horses. Irrespective of aetiology, THO frequently results in pain or fracture of the petrous temporal bone during normal movement of the tongue and larynx. In an effort to decrease pain and reduce the likelihood of petrous temporal bone fracture, partial stylohyoidectomy and ceratohyoidectomy have been developed. Serious complications have been reported following stylohyoidectomy and therefore the current recommendation is to perform unilateral ceratohyoidectomy. Benefits of ceratohyoidectomy include a lower risk of vascular and nerve damage and a reduced risk of clinical signs recurrence when compared with stylohyoidectomy. This report describes a case of THO in which clinical signs recurred approximately 2 years after unilateral ceratohyoidectomy was performed. Due to this complication, resection of the contralateral ceratohyoid bone was performed, which resulted in complete resolution of clinical signs. Although the clinical signs are frequently unilateral, the disease is most commonly a progressive bilateral condition and some horses may not have complete resolution of clinical signs when unilateral ceratohyoidectomy is performed. Therefore, if clinical signs persist after unilateral ceratohyoidectomy, a therapeutic consideration should include bilateral ceratohyoidectomy. This report suggests a favourable short‐term prognosis for a horse treated with bilateral ceratohyoidectomy.     

Temporohyoid osteoarthropathy in two young horses

Two cases of temporohyoid osteoarthropathy (THO) in young Australian horses are described. The pathogenesis of THO is yet to be fully elucidated, but current theories include extension of infection from otitis media or interna to the temporohyoid joint or a primary but non‐infectious degenerative condition within the temporohyoid joint. The young age of the horses and the unilateral distribution suggested an infectious aetiology. Both horses partially responded to treatment with broad‐spectrum antimicrobial and anti‐inflammatory drugs with concurrent management of ulcerative keratitis. The management of violent head shaking in one horse included the administration of gabapentin, an anticonvulsant known to have antihyperalgesic effects and reduce neuropathic pain.     

Temporohyoid osteoarthropathy in 33 horses (1993-2000)

A retrospective study of the medical records of 33 horses was performed to determine the clinical and diagnostic abnormalities associated with temporohyoid osteoarthropathy. Data collected from medical records included signalment, presenting complaints, history, physical examination findings, laboratory data, results of diagnostic imaging studies, and treatments. Follow-up information was obtained from a review of case records; by telephone conversation with the owner, veterinarian, or trainer; or by both methods. Of 33 horses with temporohyoid osteoarthropathy, 29 presented with facial nerve (cranial nerve VII) deficits and 23 presented with vestibulocochlear nerve (cranial nerve VIII) deficits. Guttural pouch endoscopy was more reliable than radiography for diagnosis. Of horses with unilateral clinical signs, 22.6% actually had bilateral disease. Magnetic resonance imaging and computed tomography identified the lesions in all horses in which these tests were performed. Of 30 horses for which follow-up information was obtained, 20 (67%) were alive. Eight horses were euthanized and 1 died because of problems associated with temporohyoid osteoarthropathy. Nineteen of 20 surviving horses (95%) were considered by the owner or trainer to be suitable for athletic use. Twelve surviving horses (60%) had residual facial nerve deficits; 11 horses (55%) had residual vestibulocochlear nerve deficits. Horses with temporohyoid osteoarthropathy have a fair prognosis for return to some type of athletic function, but there is risk of acute death. The majority of horses would be expected to have some residual cranial nerve dysfunction, and it could take a year or longer for maximal improvement to occur.     

Successful treatment of a horse with presumed parasitic encephalitis

Verminous myeloencephalitis is a rare, but predominately fatal, cause of neurological disease in horses. A 6‐year‐old mare was admitted to the Royal Veterinary College Equine Referral Hospital following acute onset of depression, central unilateral blindness and compromised vision in the opposite eye. Based on pronounced eosinophilic inflammation detected in the cerebrospinal fluid (CSF) and diagnostic imaging findings indicating a space‐occupying lesion within the brain, a presumptive diagnosis of aberrant parasitic migration causing parasitic encephalitis was made. Treatment consisted of anti‐inflammatories and high doses of an anthelmintic. The horse's condition improved, the neurological deficits and observed space‐occupying lesion within the brain resolved completely and the mare returned to full work. To the authors’ knowledge, this is the first report describing complete recovery from suspected aberrant parasite migration in the CNS and will hopefully encourage treatment of suspected cases in the future.     

Traumatic bilateral stylohyoid bone fracture in an Appaloosa

An Appaloosa gelding presented for a traumatic puncture wound of the head ventral to the base of his left ear, bilateral epistaxis and upper respiratory compromise. The horse did not exhibit dysphagia or cranial nerve deficits. The horse suffered bilateral oblique fractures of both stylohyoid bones due to the traumatic incident, diagnosed upon endoscopy of the guttural pouches. Treatment consisted of anti‐inflammatory medication, broad‐spectrum antibiotics, guttural pouch lavage and dietary management with soft feeds. At a one‐month follow‐up examination, endoscopic evaluation revealed a union at both stylohyoid bone fracture sites. Guttural pouch mycosis was diagnosed in the left guttural pouch on the lateral wall at the entrance of the lateral compartment. The guttural pouch mycosis was treated with a nystatin and gentamicin flush, followed by a course of oral fluconazole. At the 3‐month re‐evaluation, the guttural pouch mycosis had completely responded to treatment.     

Episodic collapse in the horse

The term ‘collapse’ can be used to describe a variety of incidents in which a horse loses postural tone with or without progression to recumbency and with or without loss of consciousness. Depending on the aetiology of the condition the episode may be self‐limiting and may or may not recur. Alternatively the collapse may be secondary to serious injury or disease and require veterinary intervention. This article mainly discusses investigation of the former scenario of self‐limiting single or multiple episodes of collapse in apparently healthy horses. An overview of the various causes of collapse is followed by a suggested approach to the diagnosis of these challenging cases.     

Caffeine clearance in the horse

The pharmacokinetic properties of intravenously administered caffeine were studied in 10 horses using a commercially available automated enzyme immunoassay. The harmonic mean for the distribution half-life was 5.2 min (range 1.4–18.7). The harmonic mean for the elimination half-life was 10.18 h (range 6.82–20.92). The harmonic mean of the volume of distribution was 0.32 L/kg (range 0.22–0.53). There was no correlation between the dose of caffeine/kg body weight and the elimination half-life (Spearman's coefficient of rank correlation =0.19).Abbreviations AUC area under the serum concentration-time curve - AUMC area under the moment curve - BSP sulphobromophthalein - ICG indocyanine green - SD standard deviation - t _1/2 elimination half-life - V _c apparent volume of the central compartment - V _d(ss) apparent volume of distribution at steady state     

Uveitic glaucoma in the horse

Glaucoma is a serious complication of anterior uveitis that can result in significant ocular discomfort and loss of vision. As glaucoma is insidious and mostly asymptomatic until late in the course of disease, it is often undiagnosed. Equine recurrent uveitis is the most common underlying disorder: it is a disease of high prevalence, characterised by recurrent‐remitting episodes of ocular inflammation. Here, the inflammatory cells and mediators they release alter the normal anatomic structure of the anterior chamber and aqueous drainage pathways of the eye. These changes alter the homeostatic mechanisms of intraocular pressure control. Management of glaucoma secondary to uveitis can be challenging due to the difficulties of managing the underlying disorder and its effects on the eye. This article reviews the pathogenesis of uveitic glaucoma in the horse and medical and surgical management options.     

Ophthalmic antimicrobial therapy in the horse

Effective antimicrobial therapy of infectious ocular disease in the horse may be difficult to achieve. This paper reviews the routes of delivery, the pharmacokinetics and the bioavailability of the various antimicrobial agents used in the treatment of ocular infection in the horse. The modes of action and the criteria for selection of the common antibacterial, antimycotic and antiviral drugs used are described.     

Haemangiosarcoma in the horse

Neoplasms arising from vascular endothelial cells include benign haemangioma and malignant haemangiosarcoma, both of which are rare in the horse. Haemangiosarcoma can arise as a solitary mass, typically involving the eye or skin, or as disseminated tumours throughout multiple organs. There is no sex, breed or age predilection but most cases are found in middle aged horses. Clinical presentations of haemangiosarcoma in the horse include the presence of a visible mass or reflect dysfunction of the organ involved, thus making it difficult to differentiate from other neoplasms. Ante mortem diagnosis through clinicopathological findings, cytological findings of body cavity effusions or fine needle aspirates are often unrewarding. Biopsy or mass submission for histopathological examination may aid in diagnosis of haemangiosarcoma. A majority of cases are diagnosed post mortem; however, if the mass is poorly differentiated additional diagnostics such as immunohistochemical staining may be needed. Unfortunately, treatment of haemangiosarcoma is often unrewarding and limited based on the location of the mass and the aggressive nature of this neoplasm.     

Corneal esthesiometry in the healthy horse

Objective To determine corneal sensitivity in healthy adult horses in order to establish reference values. Animals studied One hundred eyes of 50 healthy adult horses. Procedure Corneal sensitivity was determined by evaluating the corneal touch threshold (CTT) in five different corneal regions using a Cochet‐Bonnet esthesiometer. Results Comparing CTT values (in mm filament length) of the five prescribed corneal regions revealed regional variations in corneal sensitivity, with the central region (21.15 ± 6.23 mm) being the most sensitive, followed by the nasal (20.75 ± 5.14 mm), temporal (20.70 ± 5.37 mm), ventral (20.15 ± 5.88 mm) and dorsal (15.85 ± 3.70 mm) region. However, differences between the central, nasal, temporal and ventral regions were not statistically significant, whereas the dorsal region was significantly (P < 0.0001) less sensitive compared to the other regions. Division of the horses into three age groups revealed an insignificant decrease in corneal sensitivity with age in the nasal, temporal, ventral and central region, and an insignificant increase with age in the dorsal region. Correlation of corneal sensitivity with age was statistically significant in the central, ventral and temporal region. No statistically significant difference in the CTT was found between left and right eyes and between males and females. Conclusions CTT values in 100 eyes of 50 healthy adult horses evaluated with a Cochet‐Bonnet esthesiometer generated reference values. Reference values are necessary to determine alterations of corneal sensation accompanying various eye diseases or systemic diseases.     

Evaluation of ataxia in the horse

Ataxia in the horse is a common clinical presentation requiring a methodical approach for accurate neurolocalisation. Observed neurological deficiencies should support a localised single aetiology whenever possible. Relevant differential diagnoses should be considered based on the case history and localisation. Diagnostic strategies can then be applied relative to disease risk.