Headshaking

Question 1

List treatment options and proposed success rates for trigemenal mediated headshaking

Answer 1

1. Nose nets - up to 70% relief in 25% cases. Works through ‘gate theory’ - closing the gate to pain by stimulating touch receptors. Cheap and therefore worth a try
2. Pharmaceuticals a) Gabapentin - not specifically studied in headshaking and ↓ oral bioavailability
   b) Carbemazapine (Na⁺ blcking anticonvulsant) +/- cyproheptadine (centrally acting antihistamine and serotonin antagonist) may be useful in people but can cause drowsiness and can’t compete so limited clinical applicability
3. PENS - Initial 3 procedures, first 2 1 week apart then a third approx 3 wk later. Had 8.8% complication rate (almost all mild) and rx in remission of headshaking following the initial course in 53% (72/136) horses. Median remission time 15.5 weeks after 3rd tx. Where signs recurred, most went back into remission following future procedures usually for longer time than w previous tx. Approx 50% returning to similar exercise levels as prev
4. Electroacupuncture - 6 cases reported by Devereaux (2019 EVE) - Median remission time for 1st tx was 5.5 days (mean 7.6 days, range 0–13 days, n = 6), 2nd tx 8.5 days (mean 10.6 days, range 7–21 days, n = 6), 3rd tx 18 days (mean 28.8 days, range 6–71 days, n = 6), 4th tx 47.5 days (mean 10 weeks, range 11 days–23 weeks, n = 6), 5th tx 13 weeks 5 days (mean 18 weeks 5 days, range 5 weeks–46 weeks, n = 5), 6th tx 24 days (mean 26 days, range 13–41 days, n = 3).
5. Surgery - Caudal ablation of the infraorbital nerve via coil compression rx in approx 50% success rate in 57 horses but 26% relapsed with a median time of 9 months (2mo-5yr). Most developed nose rubbing; short-term in majority but 4/58 were euthanised dt severity or nonresolution of rubbing

Question 2

Which nerve block/blocks can be used in the dx of trigeminal mediated headshaking (TMH)?

Answer 2

1. Maxillary:
2. Infra-orbtal: fairly useless as unlikely to get sufficient retrograde diffusion to desensitise all affected portions of the nerve.
3. Posterior ethmoidal - branch of the maxillary; in other texts has been referred to as caudal anaesthesia of the infraorbital nerve by Roberts et al. (2013) and caudal nasal nerve block by Dyce et al. (2002). It branches off the maxillary nerve just proximal to the maxillary foramen and enters the caudal nasal foramen before running towards the dorsal meatus of the nasal cavity to innervate the nasal mucosa. Upto 81% improvement post block in cases of TMH