Trigeminal neuropathy in two horses following trauma to the infraorbital and mental nerves

Abstract

This case series describes two cases of a head injury resulting in a traumatic neuropathy of the infraorbital nerve and the mental nerve, respectively. Both cases presented with head-shaking behaviour and assumed facial dysaesthesia. This is a cause of head-shaking not previously described in horses. One horse (Case 1) had a small wound at the level of the infraorbital foramen and was diagnosed with a bony fragment adjacent to the infraorbital nerve using computed tomography (CT) and ultrasonography. Treatment consisted of surgical removal of the fragment, systemic anti-inflammatories and multimodal analgesia. The second case (Case 2) was diagnosed with a nondisplaced comminuted fracture of the right hemi-mandible using CT. The fracture line, along with multiple small fragments, was overlying the mental nerve as the nerve exits the mental foramen. The horse was treated with multimodal analgesia, and the fracture healed without requiring stabilisation. Clinical signs took several months to resolve in both cases. There were no reported signs of dysaesthesia or head-shaking 6 months (Case 1) and 4 months (Case 2) following diagnosis. Long-term follow-up is still required to assess these horses. Traumatic neuropathy should be considered as a differential diagnosis in horses presenting with headshaking behaviour.

Trigeminal‐mediated headshaking: A diagnostic challenge

“…This is in contrast to the cases of human trigeminal neuralgia where reductions in conduction velocity and ephaptic conduction occur due to demyelination of the trigeminal nerve caused by focal compression at the root entry zone (Devor et al, 2002). It is likely, given the traumatic aetiology, that neurophysiologic alterations would have been present in the cases reported by Ogden et al (2023).…”

“…The term 'equine trigeminal-mediated headshaking' (TMHS) has replaced the previously used diagnosis of 'idiopathic headshaking' to reflect the clinical signs, which are considered to characterise trigeminal neuropathic pain (Pickles et al, 2014). This diagnosis is reserved for horses with a presumed functional, rather than structural, disorder of the trigeminal nerve, as distinct from horses such as those described in the case series by Ogden et al (2022) where gross pathology, in this case trauma of trigeminal nerve branches, induces clinical signs of headshaking.…”

“…Other pathological or behavioural causes of headshaking behaviour, as listed by Ogden et al (2022), have also been described. It is only by exclusion of these other causes, or via invasive neurophysiological studies which are outwith the realm of clinical practice, that a diagnosis of TMHS can be confidently assigned.…”

“…A gross pathological cause of headshaking behaviour is only rarely diagnosed (Pickles et al, 2014), and therefore, it can be tempting to try and take shortcuts in the diagnostic procedure; however, if we do not look for these other causes, we will surely not find them. Indeed, Ogden et al (2023) report that the traumatic skin lesion in one of their cases was disregarded as self‐inflicted from headshaking‐induced muzzle rubbing by the initial treating veterinary surgeon. Careful anamnesis, physical examination and often diagnostic imaging are therefore required for correct diagnosis (Pickles et al, 2014).…”

Complications of Equine Cheek Teeth Extractions

“…Thankfully most cases show spontaneous resolution of clinical signs within 1 to 2 weeks of nerve injury. However, some cases of trigeminal damage can cause longer term headshaking (Ogden et al 2022). Infraorbital nerve damage is much less likely following Steinmann pin repulsion, but long term signs of clinical trigeminal neuropathy can rarely occur following use of this technique.…”