The neurological horse with normal mentation - miscellaneous

Question 1

Examples

Answer 1

• head-shaking
• sleep-deprivation (or narcolepsy)
• ‘shivers’

Question 2

Head-shaking - CS

Answer 2

Involuntary sudden violent repetitive movements of the head torso-ventrally, horizontally or rotatory

Additionally can see
- nose rubbing on stationary objects/floor/scratching
- lower head carriage
- snorting, sneezing, snoring
- excessive nasal discharge

Question 3

Head-shaking - cause

Answer 3

90% are considered idiopathic

Symptomatic
- cause found and withdrawal permanently removes the problem.

Persistent:
- thought to be trigeminal mediated due to an abnormal nerve transmission of a facial noxious sensation

Identified triggers
- photic: bright light, photoperiod, cystic corpora nigra, floaters in the posterior/anterior chamber
- allergic: rhinitis
- sinusitis, otitis (Trombicula autumnal), GP mycosis
- structural: skul fractures, dental dz, THO, TMJ
- bit/bridle

Question 4

Head-shaking - Grades

Answer 4

Grade 0 - no head-shaking

Grade 1 - head-shaking, only at exercise but sufficiently mild that the horse may be ridden

Grade 2 - head-shaking at exercise to a severity as to make ridden exercise unsafe or impossible

Grade 3 - head-shaking even at rest

Question 5

Head-shaking - seasonality?

Answer 5

• April-summer

Question 6

Head-shaking - diagnostic plan

Answer 6

Identification of potential triggers is critical
- physical exam/environment/management
- ocular exam
- dental exam
- upper airway endoscopy including GP
- nerve blocks (infraorbital and maxillary)
- skull x-rays / CT
— strongly recommend CT early on as offers detailed evaluation of the structures within the head e.g. sinuses, TMJ and temporal hyoid joints
- otoscopy

Question 7

Head-shaking - medical tx

Answer 7

Best improvement with
- Cyproheptadine 0.3mg/kg PO BID + carbamazepine 4mg/kg
- nose nets (1/3 cases 70% improvement)
- ocular sunglasses (50-70% improvmement)

Other options:
- gabapentin 25mg/kg q8h
- steroids (inhaled)
- magnesium sulphate 40mg/kg
- antihistamines
- melatonin 4mg/kg q6h
- bridles bit

Question 8

Head-shaking - surgical therapy

Answer 8

• infraorbital neurectomy with cryotherapy
  — remission in 16% horses
• chemical sclerosis of the infraorbital with phenol
• caudal compression of the infraorbital nerve (infraobrtal canal)

Surgical therapy have been described and attempted with low success and high post-op complications

Question 9

Head-shaking - other therapies

Answer 9

EquiPENNS
- (percutaneous nerve stimulation)
- 53% return to previous level of work for a variable length of time
- response to stimulation: 3 treatments needed
- 8% adverse reactions

Electro-acupuncture
- small study with only 6 horses
- short remission time

Question 10

Narcolepsy - what is it?

Answer 10

Spectrum of CND (chronic neurologic disorders) characterised by episodes of excessive sleepiness, muscular weakness and REM onset sleep

Question 11

Narcolepsy - potential causes

Answer 11

Believed to be due to dysfunctional orexin system causing low hypocretin concentrations in the CSF

Familiar in several breeds:
- Lipizzaner, miniature breeds and Shetland ponies

Question 12

Sleep-deprivation - what is it?

Answer 12

• episodes of collapse due to lack of regular resting/sleep

Question 13

Sleep-deprivation - causes

Answer 13

• chronic arthritis
• chronic pain
• fear to environment (stress)

Question 14

What is more common clinically - sleep-deprivation or true narcolepsy?

Answer 14

• sleep-deprivation

Question 15

Sleep-deprivation/narcolepsy - CS

Answer 15

• staggering, lowering of the head and neck, buckling of the thoracic limbs, kneeling posture, flaccidity of lips
• unexplained abrasions, wounds (knees, lips) (i.e. consequence of unobserved episode)
• kneeling when tightening of the girth
• partial or total collapse during normal activities of the day

Question 16

Sleep-deprivation/narcolepsy - diagnosis

Answer 16

• age, recent changes in environment, stable, barn, premises, wildlife
• concurrent dz: arthritis, back, hocks, carpus, PPID
• quality of bedding, tight rugs in winter
• true narcolepsy: rule out dx

Question 17

Sleep-deprivation/narcolepsy - tx

Answer 17

• bute-trial: oral phenylbutazone (for several weeks)
• thick bedding: straw
• large stable
• inside barn
• remove rugs
• make their environment more ‘safe’

Question 18

What is shivers? What is it characterised by?

Answer 18

• progressive, chronic neuromuscular dz in horses
• characterised by gait abnormalities when backing up, trembling of the tail while held erect, trembling of the thigh muscles and a flexed and trembling hindlimb when held

Question 19

Shivers - cause

Answer 19

• cerebellar disease caused by damage of the deep cerebellar nuclei
  — fine-tune of planned movements: flexion & extension activated at the same time

Question 20

Shivers - CS

Answer 20

Backing manoeuvre
- hyperextension of hindlimbs
- instability of picking up the hindlimbs
- offers contralateral limb
- hyperextension

But normal ambulation otherwise
- walk forward
- trot
- cantering
- performing

Question 21

Shivers vs stringhalt

Answer 21

Shivers = abnormal movement of the pelvic limbs with a hyperextension that occurs when horses are backing up

Stringhalt = abnormal fixation of the pelvic limbs when moving forwards

Question 22

Shivers - when does it normally start? what is the progression?

Answer 22

• normally starts around 5y/o
• normally progressive and performance limiting

Question 23

Shivers - diagnosis

Answer 23

• rule out other conditions: upper fixation patella, stifle OA, sacro-iliac pain

Question 24

Shivers - tx

Answer 24

• none
• guarded prognosis