How to: Manage Temporohyoid Osteoarthropathy

Disease background

Temporohyoid osteoarthropathy (THO) is an uncommon condition of horses affecting the stylohyoid and petrous temporal bones and the temporohyoid joint. Osseous proliferation, degenerative joint changes and ankylosis of the joint develop, compromising normal movement. While the condition may be clinically silent or associated with non-specific signs, signs of cranial nerve dysfunction result from fracture of the petrous temporal bone and/or stylohyoid bone subsequent to abnormal biomechanical forces with movement of the tongue/head. The neurological dysfunction presents challenges for treatment and management of affected horses. Furthermore, prevention of neurological disease or management for non-neurological manifestations in horses with THO may be goals of treatment.The aetiopathogenesis of THO is unknown, although otitis media-interna from local or haematogenous spread of bacteria, non-septic degenerative arthrosis of the temporohyoid (TH) articulation or traumatic injury to the TH region have been proposed (Divers et al. 2006). The disease is most commonly diagnosed in middle-aged horses, although younger animals may be affected (Readford et al. 2013). Non-neurological signs may be present, including head shaking, difficulty/reluctance to chew, pain on palpation of the ear base, resentment of bridle placement and behavioural changes (Divers et al. 2006). With progressive TH ankylosis, risk of fracture of the petrous temporal bone increases, especially with sudden movement of the hyoid apparatus during vocalisation, forceful head movement, head trauma or manipulative procedures such as nasogastric intubation or dentistry. Fracture of the petrous temporal bone often results in acute onset of facial and/or vestibular dysfunction including drooping of the lower lip and ear, ptosis and packing of feed in the buccal pouch on the affected side, deviation of the muzzle away from the affected side, head tilt, body lean, nystagmus and occasionally recumbency with an inability to rise due to severe disorientation. Signs of dysphagia are occasionally present due to damage to the vagus and/or glossopharyngeal nerves and CNS dysfunction (e.g. seizures, meningitis) may develop if bones of the calvarium are involved. Ipsilateral exposure keratitis and keratoconjunctivitis sicca (KCS) can result from damage to parasympathetic fibres accompanying the facial nerve in the petrous temporal bone.Diagnosis is achieved through consideration of signalment and clinical signs, guttural pouch endoscopy, radiography, scintigraphy, CT or MRI. Cytological and microbiological diagnosis of otitis media-interna can be achieved through tympanocentesis and lavage (Slovis 2012).TreatmentGiven the aetiopathological possibilities and clinical abnormalities of THO, the principles of treatment involve:1.Decreasing inflammation and inflammatory fluid accumulation at the TH joint (± fracture site)2.Decreasing pain associated with osteitis, joint disease and fracture3.Antimicrobial treatment for confirmed/suspected bacterial otitis media-interna and meningitis4.Treatment of exposure keratitis and KCS5.Stabilisation of the TH articulation to prevent fracture or ongoing trauma at a fractured site.Treatment of inflammation and pain can be achieved through systemic administration of non-steroidal anti-inflammatory drugs or corticosteroids, although if infection is suspected, corticosteroids should be avoided. In addition, gabapentin has been proposed for treatment of neuropathic pain in THO (Readford et al. 2013); however clinical efficacy in horses is unknown.When primary or secondary bacterial involvement is suspected/confirmed through tympanocentesis and/or CSF analysis, antimicrobial selection should be based on culture and sensitivity testing or likely organisms involved in otitis media-interna: e.g. Staphyloccocus, Streptococcus, Corynebacterium, Actinobacillus and Salmonella species (Rand et al. 2012). In addition, antimicrobials that cross the blood:CSF and blood:brain barriers should be selected when CNS involvement is present: e.g. trimethoprim-sulphonamide combinations or 3rd generation cephalosporins. Antimicrobial treatment of otitis media-interna and/or CNS infection requires long-term administration (≥30 days). Determination of when to discontinue treatment can be difficult, and may involve results of diagnostic testing and/or clinical response.Exposure keratitis and KCS should be managed through treatment of existing corneal ulceration (topical antimicrobials, atropine) and protection of the ocular surface (artificial tears, ocular lubricants, temporary partial tarsorrhaphy). Surgical procedures (partial stylohyoidectomy, ceratohyoidectomy) to prevent fracture or clinical deterioration in horses with THO have been described. The aim of surgical treatment is to decrease movement and abnormal biomechanical forces on the TH joint. Currently, the surgical treatment considered most effective is ceratohyoidectomy (Divers et al. 2006), although controlled studies comparing the efficacy and outcomes of surgical versus medical treatment of THO is lacking. Nevertheless, good outcomes in horses after ceratohyoidectomy have been described (Pease et al. 2004; Divers et al. 2006)PrognosisThe prognosis for THO is guarded to fair and dependant on severity of pathology and clinical signs, whether bilateral disease (pathologically and/or clinically) is present and whether residual neurological signs result. Most horses improve with treatment and many are able to return to some athletic function, although residual cranial nerve dysfunction is not uncommon and time periods of > 1 year may be required for maximum improvement. In a retrospective study, of 30 horses with THO and long-term follow-up information, 66% survived: 70% returned to athletic function, time to resolution/stabilisation of signs was up to 2 years and 60% and 55% had residual facial or vestibulocochlear deficits, respectively (Walker et al. 2002).ReferencesDivers, T.J., Ducharme, N.G., de Lahunta, A., Irby, N.L. and Scrivani, P.V. (2006) Temporohyoid osteoarthropathy. Clin Tech. Equine Pract. 5, 17-23.Pease, A.P., van Biervliet, J., Dykes, N.L., Divers, T.J. and Ducharme, N.G. (2004) Complication of partial stylohyoidectomy for treatment of temporohyoid oseteoarthropathy and an alternative surgical technique in three cases. Equine Vet. J. 36, 546-550.Rand, C.L., Hall, T.L., Aleman, M. and Spier, S.J. (2012) Otitis media-interna and secondary meningitis associated with Corynebacterium pseudotuberculosis infection in a horse. Equine Vet. Educ. 24, 271-275.Readford, P.K., Lester, G.D. and Secombe, C.J. (2013) Temporohyoid osteoarthropathy in two young horses. Aust. Vet. J. In press.Slovis, N. (2012) Equine otitis media-interna. Equine Vet. Educ. 24, 276-278.Walker, A.M., Sellon, D.C., Cornelisse, C.J., Hines, M.T., Ragle, C.A., Cohen, N. And Schott, H.C. (2002) temporohyoid osteoarthropathy in 33 horses (1993-2000). J. Vet. Intern. Med. 16, 697