Adult Equine: Nervous System Diseases Flashcards
What are the possible DDx of Intracranial Diseases?
- Head trauma
- Ischemia
- Infection: Meningitis or Encephalomyelitis
- Space occupying lesions
- Toxins
- Narcolepsy
What are the most commonly affected areas of the skull with head trauma in the horse?
Adults: petrous temporal bone, basi-occipital bone and basi-sphenoid bone are all common areas of fracture due to rearing up and hitting the back of the head
Foals: entire skull due to being kicked by the foal
What are the clinical signs associated with head trauma in the horse?
- Neurological signs are usually immediate
- Cerebral signs: depression, dementia, excitation or recumbent
+/- brain stem/ cranial nerve signs: head tilt or facial nerve paralysis
- Epistaxis: bleeding into guttural pouches or sinus trauma
- Bleeding from the ear
- Seizures: can be facial grimacing, twitching, rapid eye movements or blinking, paddling, tonic posturing or extensor rigidity
You notice a horse is having seizures (anything including facial grimacing, twitching, rapid eye movements or blinking, paddling, tonic posturing or extensor rigidity), what is the treatment of choice for seizures in the horse?
What are the other treatments available?
Treatment of choice:
- Diazepam: 0.02 - 0.2 mg/kg IV
Other:
- Phenobarbital: 12-20 mg/kg IV in 30mls saline, then 2.2-11 mg/kg PO SID-BID
- NSAIDs or Steroids
- Stall padding to prevent further injury
Caution: NO Acepromazine or Ketamine!
What is the prognosis of seizures in horses?
Prognosis is guarded in adult horses as they are difficult to manage, and involvement of the cranial nerves worsens the prognosis, especially if chewing or swallowing is affected
What are the most common causes of brain ischemia in the adult horse?
1) Anesthesia/ Post-anesthesia due to hypoxic or hypercapnic periods
note: damage can be focal or extensive
2) Intra-carotid Injection: the common carotid artery is very close to the jugular vein (reactions will occur in 5-30 seconds post-injection)
What are the clinical signs associated with brain ischemia in the horse following anesthesia?
- Blindness
- Abnormal behavior: altered mentation/ behaviour
- Seizures
What is the treatment for suspected brain ischemia in the adult horse, due to hypoxia/ hypercapnia post-anesthesia?
- Supportive: provide oxygen, and stall padding
- Control seizures with Diazepam
What is the prognosis associated with brain ischemia in the adult horse?
Guarded to poor- depending on the areas of the brain affected and if there is cranial nerve involvement, especially if chewing and swallowing is affected
Intra-carotid injection with:
- Xylazine (water-soluble): the horse generally regains consciousness within an hour and recovers completely in a week = good prognosis
- Procaine penicillin (oil-based): may warrant euthanasia due to cerebral damage
What is the treatment for suspected brain ischemia in the adult horse, due to intra-carotid injection?
- Supportive: provide oxygen, and stall padding
- Control seizures with Diazepam
What is the most common cause of meningitis in the adult horse?
What is the prevalence of meningitis in the adult horse?
Usually bacterial spread hematogenously from another site of infection
Prevalence: uncommon in adults
What are the clinical signs associated with meningitis in horses?
- Depression
- Coma
- Cervical stiffness
- Seizures
How can Meningitis be diagnosed in the horse?
- Blood-work
- CSF cytology + culture
- Blood culture
How can Meningitis be treated in the horse?
- IV broad-spectrum antibiotics (4-6 weeks minimum) based on culture + sensitivity
- NSAIDs or steroids + supportive care + Control seizures with Diazepam
What infectious agents can cause Encephalomyelitis in horses?
- Eastern, Western and Venezuelan Equine Encephalitis viruses
- West Nile Virus
- Rabies
- Borna Disease Virus
- Equine Herpes Virus-1
What are the clinical signs associated with Encephalomyelitis in horses?
- Fever, anorexia, stiffness
- Paralysis of larynx, pharynx and tongue
- Propulsive walking and depression
- Dog-sitting leading to recumbency
note: Equine Herpes Virus-1 is usually ascending, thus will start in the hind end with urinary incontinence and work its way up
What is the treatment for Encephalomyelitis in horses?
What is the prognosis of Encephalomyelitis in horses?
- Supportive care
- Anticonvulsants
- Steroids
- Anti-viral drugs can be tried: acyclovir and valacyclovir
Depends on the offending agent:
- WNV and EHV = guarded to poor
- Others = guarded to grave
What are the usual causes of Space-occupying masses in the equine skull/ brian?
- Abscess: usually a form of bastard Strangles
- Granuloma
- Neoplasia: lymphosarcoma or melanomas
+/- Hydrocephalus if the space-occupying lesion obstructs the flow of CSF
How can space-occupying masses be diagnosed in the equine skull/ brain?
CT or MRI
What are the toxins that can lead to neurological signs in the horse?
- Ragwort poisoning: leading to hepatic encephalopathy
- Mycotoxins: leading to grass staggers
- Fusarium B: leading to Mouldy Corn Disease
- Yellow Star Thistle
- Lead
How can toxicity be treated in the adult horse?
- Remove the offending toxin by removing it from the diet/ pasture
- Supportive care
What is the cause of Narcolepsy in horses?
The current thought is due to a lack of sleep
- Perhaps a dominant animal in a group feels it can’t fall asleep to protect the group
- Maybe the animal has pain and is unable to sleep or lie down
What are the clinical signs associated with Narcolepsy in the horse?
- Episodes up to 10 minutes: usually occurring during grooming, hosing down after exercise, eating/ drinking, or being pet
- Most remain standing with a low hanging head and closed eyelids
- Horses may buckle to their knees or fetlocks and develop pressure sores here
What is the treatment of Narcolepsy in the horse?
What is the prognosis of Narcolepsy in horses?
- No real treatment, but if the cause of the sleep deprivation is pain, then a Bute trial can be done
Prognosis:
- Young horses may grow out of it
- Life long problem in adults and thus safety for both the horse and the owner need to be considered e.g. don’t want the horse to fall on you while you are grooming it
What is the treatment for Facial Nerve Paralysis in the adult horse, post recumbency?
- Topical anti-inflammatory: Voltarol
- Eye lube IF the lacrimal nerve has been affected too
What causes Horner’s Syndrome in the horse?
Damage to the ascending sympathetic nerves in the vago-sympathetic trunk (sits in the jugular groove)
Most commonly associated with:
- Perivascular injections, where the injection is accidentally placed around the jugular vein, putting pressure or blocking the impulses along the vago-sympathetic trunk
- Guttural pouch disease, where the cranial-cervical ganglia sits on top of the dorsal part of the guttural pouch
What are the clinical signs of Horner’s Syndrome in the horse?
- Miosis: pupil constriction
- Enopthalmos: posterior displacement of the eyeball
- -> + prolapsed 3rd eyelid in these cases
- Ptosis
- Sweating of the neck of the side of the lesion
What is the cause of Tempero-hyoid osteopathy in horses?
- We used to think it was due to an extending infection from the otitis media
- We now believe it is due to Degenerative Joint Disease in the Tempero-hyoid joint with bony proliferations forming
What are the clinical signs associated with Tempero-hyoid Osteopathy in horses?
- Behaviour changes: head shaking, ear rubbing, and avoiding the bit
- If a stress fracture forms because of it, this can lead to facial nerve paralysis, corneal ulceration (lacrimal nerve involvement), and peripheral vestibular syndrome
How can Tempero-hyoid Osteopathy in horses be diagnosed?
- Radiography of the Tempero-hyoid joint
- Endoscopy of the Guttural Pouch
- CT
What is the treatment of Tempero-hyoid Osteopathy in horses?
- If the cause is due to DJD of the Tempero-hyoid joint + Boney proliferation: NSAIDs + Prophylactic surgery of the hyoid apparatus may be indicated to prevent a stress fracture from occurring
- If the lacrimal nerve branch of the facial nerve is involved, then eye lubrication will be needed
What is the prognosis of Tempero-hyoid Osteopathy in horses?
- Fair to guarded for athletic performance
- May get residual deficits of CN 7 and 8 and therefore even casual riding may be risky
What is Cauda equina neuritis (aka polyneuritis equi)?
A chronic granulomatous inflammation of the cauda equina, thought to be due to an immune-mediated condition.
This condition can involve more nerves than just the cauda equina (such as the cranial nerves/ brachial plexus) and therefore was renamed Polyneuritis equi
What are the clinical signs/ presentations of horses with Polyneuritis equi?
- Hyperesthesia, analgesia or areflexia of the perineal area
- Paralysis of the tail, anus and perineum
- Paralysis of the rectum + bladder: leading to impactions and chronic cystitis
+/- CN signs of 5, 7 and 8 or the brachial plexus
+/- Pelvic limb ataxia, weakness or muscle atrophy: uncommon
How can Polyneuritis equi be diagnosed?
There is no Ante-mortem tests available, so the diagnosis is based on clinical signs and ruling out other conditions (e.g. Sacral fracture)
How is Polyneuritis equi treated?
What is the prognosis of Polyneuritis equi?
Tx: Supportive and non-specific, treat the horse depending on the signs e.g. treat the incontinence or UTI’s
Prognosis:
- Poor: this is a progressive disease and may progress rapidly or slowly
What are the DDx of the spinal cord diseases in the horse?
- Trauma
- Infection: Osteomyelitis
- Cervical vertebral malformation/ cervical stenotic myelopathy (Wobbler’s Syndrome)
- Verminous Meningoencephalomyelitis
- Equine herpesvirus-1 myeloencephalopathy
- Equine Degenerative Myeloencephalopathy
What are the common sites of trauma along the spine of the horse?
1) Occipito-atlanto-axial region: due to rearing up and falling back, or neck hyper-flexion, leading to fractures or avulsions of the rectus capitus muscle, where it attaches to the occipital bone
2) Caudal cervical region: due to neck hyper-flexion
3) Mid-thoracic to cranial lumbar back: due to falling on its back (usually due to jumping accidents)
4) Sacral region: due to a fall after rearing up, or running backwards into a wall
What are the clinical signs/ presentations of a traumatic spinal injury in the horse?
- Sudden onset of reluctance to move
- Ataxia and weakness
- Recumbency
- Pelvic limb gait abnormalities
- Abnormalities of urination or defecation
- Tail/ Perineal hypo-reflexia and paralysis
What is the treatment of a traumatic spinal injury in a horse?
What is the prognosis of a traumatic spinal injury in an adult horse?
1) Stabilization: sedation, airway access, looking for bleeding, control circulation/ treat shock,
2) Decrease swelling associated with the spinal trauma: Steroids, Mannitol, NSAIDs, Furosemide
3) Time + Rest
4) +/- Surgery if needed (uncommonly done)
Prognosis:
- If the horse is recumbent for 24+ hours = grave. It’s just too difficult to manage a recumbent adult horse (turning the horse to prevent pressure sores)
- Repeat neuro exam to guide prognosis
- A sacral fracture should improve by 12 weeks, if not then the prognosis is poor
How can traumatic spinal injury be diagnosed in the horse?
1) History, clinical exam, physical exam, rectal exam
2) Neurological exam
3) Radiograph/ CT
4) U/S: of the neck and pelvis
What are the most common causes of a spinal infection (vertebral osteomyelitis/ diskospondylitis)?
- Hematogenous spread from a distant infection
- Open Wound
- Injection abscesses
What are the clinical signs associated with a spinal infection (vertebral osteomyelitis/ diskospondylitis) in the horse?
- Stiff + painful neck
- Fever
- Ataxia due to pressure on the spinal cord
How can a spinal infection (vertebral osteomyelitis/ diskospondylitis) be diagnosed in the horse?
- Bloodwork: Neutrophilia + High Fibrinogen
- Cervical radiographs
- CSF Tap, culture + cytology
- Blood culture
What is the treatment for a spinal infection (vertebral osteomyelitis/ diskospondylitis) in the horse?
What is the prognosis?
- Broad-spectrum antibiotics, guided by culture and sensitivity
- NSAIDs
+/- Surgical exploration + debridement
Prognosis:
Fair to Poor
What is the layman’s term for Cervical Vertebral Stenotic Myelopathy?
Wobbler’s Syndrome
What is the proper term for Wobbler’s Syndrome?
Cervical Vertebral Stenotic Myelopathy
What happens in Wobbler’s Syndrome that leads to its clinical signs/ presentation?
- Cervical vertebral malformation results in progressive spinal cord compression and injury, leading to ataxia and paresis (wobble)
What are the 2 theories behind why Wobbler’s Syndrome happens in horses?
1) Type 1 = Developmental: a disorder of bone/ cartilage development leading to cervical vertebral malformation
2) Type 2 = Acquired Biomechanical: abnormal mechanical stresses deform the cervical column resulting in stenosis of the canal
- The equine vertebrae growth plates are susceptible to biomechanical stresses until ~5 years old when they eventually close
In reality it’s probably a mix of both
When a horse develops Wobbler’s Syndrome, there are 2 possible manifestations of it, what are they?
1) Dynamic instability: this is a dynamic compression, where there is unstable articulation between C3-C5, leading to a narrowing of the canal during cervical ventroflexion (head down)
The spinal cord becomes compressed and blood vessels are pinched or ruptured
2) Static stenosis: Regardless of the head/ neck position, you get narrowing of the canal due to thickening of the dorsal laminae bone + hypertrophy of the ligamentum flavum
An 8 - 18 month old, fast-growing male Thoroughbred presents with Wobbler’s Syndrome, which manifestation is most likely in this case?
Type 1 = Dynamic Instability: dynamic compression leading to narrowing of the canal during cervical ventroflexion (head down)
How can Wobbler’s Syndrome be diagnosed in the horse?
- Clinical signs
- Radiographs
- Myelogram
What is the treatment of Wobbler’s Syndrome in the horse?
- Rest
- Nutritional management if the horse is still young and has growing to do
- Surgical Intervention to stabilize adjacent bones is becoming more popular
- NSAIDs
What is Verminous Meningoencephalomyelitis?
Inflammation of the CNS + meninges due to the migration of strongyles and parascaris species of nematodes
What are the clinical signs associated with Verminous Meningoencephalomyelitis?
Depends on the site that is affected, but often includes: ataxia and non-specific clinical signs
How can Verminous Meningoencephalomyelitis be diagnosed?
- Exclusion of other diseases
+/- peripheral eosinophilia (this is not always seen though)
+/- High Fecal Egg Count
If Verminous Meningoencephalomyelitis is suspected, what is the treatment?
Anthelmintics + NSAIDs
- Fenbendazole (50-60 mg/kg SID 1-3 days)
- Thiabendazole (440 mg/kg SID for 2 days)
- Ivermectin (0.2 mg/kg, once)
What is the causative agent of Equine Protozoal myeloencephalitis (EPM)?
Sarcocystis neurona
What are the clinical signs associated with Equine Protozoal myeloencephalitis (EPM)?
- Usually 1-6 years old
- More common in North and South America + Canada
- Asymmetric cranial deficits
Most common Presentation are the 3A’s: Asymmetric, Ataxic and focal muscle Atrophy
How can you confirm the presence of Sarcocystis neurona?
1) Immunoblot analysis
- S. neurona antibodies in serum and CSF
CSF: Sn and Sp of 89%
Serum: Sn of 89% and Sp of 71%: BUT almost all horses will have antibodies for the parasite due to previous exposure but wont necessarily develop clinical signs
2) ELISA: Highly specific for S.neurona specific antibodies
note: You cannot do a PCR, its sensitivity is very low as Merozoites are not found in the CSF, and any free parasite DNA floating around is rapidly destroyed
3) PM: Acute hemorrhagic lesions and necrosis in the spinal cord
What is treatment for S. neurona in horses?
- Ideal drug: Ponazuril: Antiprotozoal Oral Paste, 5mg/kg/day ~28 days
- Sulfonamides: Sulfadiazine orally, 20mg/kg
- Diclazuril and Toltrazuril: coccidiostat that kills parasites in early stages, used as a prophylactic
- NSAIDs
- Vitamin E
Caution: steroids are contraindicated in this case
What is the pathophysiology as to why neurological signs are seen in horses with Equine Herpesvirus-1?
The virus causes vasculitis of the CNS arterioles, leading to edema and pressure on the NS
Can also cause hypoxic damage to the NS tissue
What are the clinical signs associated with neurological Equine Herpesvirus-1?
- Usually adults are affected (4+ years old)
- Often starts with respiratory signs
- acute hindlimb paresis + Dog sitting
- Urine scalding (bladder paresis)
+/- Cranial nerve signs
How can Equine Herpesvirus-1 be diagnosed?
- CSF Tap
- Virus isolation in the serum
- Titres
What is the treatment for Equine Herpesvirus-1?
What is the prognosis?
- Isolate the animal: it is highly contagious
- NSAIDs or Steroids (Dex 0.1 mg/kg)
+/- Antibiotics to clear secondary infections - Urinary catheter to prevent urine scalding
Prognosis:
- Most horses will recover completely IF they were never recumbent
What is Equine Degenerative Myeloencephalopathy (EDM)?
What causes EDM?
EDM is a condition characterized as a symmetric non-compressive spinal cord disease with degeneration of the white and grey matter
- Cause is Unknown: May be due to Vit E deficiency +/- genetic predisposition
It is a potential DDx for Type 1 Wobbler’s in young horses
What is the treatment for Equine Degenerative Myeloencephalopathy (EDM)?
How can EDM be prevented?
No treatment as we are unsure what causes it
Prevention:
Provide plenty of green forage to growing horses
What are the clinical signs associated with Equine Degenerative Myeloencephalopathy (EDM)?
Ataxia and paresis (wobbling)
- Same as Wobbler’s Syndrome
What are the DDx for peripheral nerve disease in the horse?
- Trauma
- Equine Motor Neuron Disease
- Grass Sickness
- Tetanus
- Botulism
- Stringhalt
- Shivering
- Headshaking
What is the pathogenesis of Equine Motor Neuron Disease?
Unknown, but thought to be related to Vit E deficiency
What can be seen on a histopathological sample of a horse with Equine Motor Neuron Disease?
- Destruction of motor nerve cell bodies in the brainstem nuclei and ventral horn grey matter, resulting in denervation atrophy of the muscles with a high percentage of Type 1 fibres (these are the slow contracting and oxygen utilizing muscles)
What are the clinical signs associated with Equine Motor Neuron Disease?
- Usually older horses with weight loss and a NORMAL appetite
- NO ataxia
- Postural weakness
- Short stride/ stumbling when moving
- When standing muscle fasciculations can be seen
- Muscle atrophy eventually develops +/- excessive recumbency
- Horses often position their feet under them to stabilize themselves (“elephant on a ball”)
How can Equine Motor Neuron Disease be diagnosed?
- Clinical signs
- Opthalmic Exam: Retinal hyperpigmentation is often seen
- Definitive diagnosis = Biopsy from the sacro-caudalis dorsalis medialis muscle (it is just beside the tail-head)
What is the treatment for Equine Motor Neuron Disease?
What is the prognosis?
No specific treatment
- Often Vit E supplementation is given
Prognosis: poor to guarded
Where are the most common locations of trauma to the peripheral nervous system?
- Supra-scapular nerve: leading to paralysis of the infraspinatus and supraspinatus muscles
- Brachial plexus: leading to a flaccid biceps, triceps and pectoralis = flaccid limb
- Radial nerve: leading to a dropped elbow and failure of protraction + flexed distal limb joints
- Cranial gluteal nerve: leading to gluteal muscle atrophy
What is the cause of Equine Grass Sickness?
- Suspected: Clostridium botulinum type C toxin
Leading to widespread destruction of the autonomic ganglia (including the myenteric and submucosal plexuses, the cardiac ganglia and the CNS ganglia)
What are the clinical signs associated with Equine Grass Sickness?
Signs of parasympathetic dysfunction:
- Dysphagia
- Constipation
- Colic
- Bloat
- Inappetance
- Weight loss
- Tachycardia
- Sweating
- Rhinitis sicca
How can Equine Grass Sickness be treated?
What is the prognosis?
Tx: supportive
Prognosis: guarded to poor = high mortality rate
What is the causative agent of Tetanus?
Clostridium tetani toxins
What is the pathophysiology of tetanus?
- C. tetani gets into a wound
- It releases its toxins
- The Tetanospasmin toxin is absorbed and carried to the pre-synaptic part of the motor endplate
- The toxin is transported to the CNS along the motor neurons to the ventral horn
- The toxin crosses the synaptic cleft to the presynaptic inhibitory interneurons
- It will inhibit the release of glycine and GABA
- This inhibits INHIBITION! Leading to Hypertonia and Muscular spasms
What are the clinical signs associated with Tetanus in the horse?
Generalized spasticity by 24 hours
- stiff gait, extended head posture
- Sawhorse stance, with the antigravity muscles most affected
- Retracted lips and ears, tail elevated
- Excessive muscle tone of the face + jaw clamped
- Profuse sweating
- Fever
Why do horses die from Tetanus?
Death is due to hypoxia and heart failure or respiratory arrest due to paralysis of the diaphragm and intercostal muscles
How can Tetanus be diagnosed?
- Clinical signs are typically enough, as well as vaccination history + titre levels
- C. tetani may be cultured from a wound
What is the treatment for Tetanus in the horse?
How can Tetanus be prevented?
- Muscle relaxation: Acepromazine or Diazepam
- Pack the ears with cotton to dampen noise
- Surgically debride the wound and flush it
- Penicillin
- Antitoxin administration
Prevention:
- Tetanus vaccine
What is the causative agent of Botulism?
Clostridium botulinum (Usually Type B toxin involved with horses)
The source is usually in hay or silage that has a pH greater than 4.5
or, contaminated commercial grain with a dead carcass
What is the pathophysiology of botulism?
- The bacteria is ingested or introduced through a wound and the toxin is released
- The toxin binds to the pre-synpatic part of the peripheral cholinergic neuromuscular junction
- The toxin binds irreversibly, leading to the blocked release of Ach
- This leads to a flaccid paralysis
- The horse must regenerate new motor endplates, which can take 4-10 days
What are the clinical signs associated with Botulism?
- Generalized muscle weakness
- Dysphagia
- Colic
- Decreased eyelid and tail tone
- Shuffling gait + dragging toes
- Reduced tongue strength + slow retraction
- Muscle tremors + recumbency
- Symmetric and progressive worsening
How can Botulism be diagnosed?
- Clinical signs + History
- Demonstration of the toxin in the wound, GI contents or feed
- Diagnosis is usually through the exclusion of similar diseases: e.g. Equine Herpesvirus-1, White Muscle Disease, Eclampsia or Equine Degenerative Myeloencephalopathy (EDM)
What is the treatment for Botulism?
How can Botulism be prevented in horses?
- Antitoxin administration
- Supportive: ventilation, IV fluids etc.
Prevention: Vaccination!
Give to the mare 6-8 weeks before foaling to ensure adequate colostrum antibodies
What is Stringhalt?
Stringhalt is a gait abnormality characterized by exaggerated upward flexion of the hindlimb that occurs at every stride at walk.
The gait abnormality usually lessens at trot and is not evident at canter. It may occur unilaterally or bilaterally
What is the cause of Stringhalt?
What is a DDx that presents similarly?
The etiology is unknown, but lesions of a peripheral neuropathy have been identified in the sciatic, peroneal, and tibial nerves.
- Possible intoxication causes
DDx: Intermittent upward fixation of the patella, or a painful lesion in the foot
What is the treatment of Stringhalt?
- Many of these cases apparently recover spontaneously
- Large doses of thiamine and phenytoin
- Severe cases: surgical resection of the lateral digital extensor tendon
What is Shivers Disease?
Shivers is a gradually progressive, chronic neuromuscular disease in horses that is characterized by difficulty in backing up. Other typical signs include trembling of the tail while held erect, trembling of the thigh muscles and a flexed and trembling hind limb
These horses often move forward just fine with no impact on racing performance
What is the cause of Shivers Disease in horses?
The ultimate causes of Shivers remain unknown. However, an extensive study published in February of 2015 revealed that the brains of horses with Shivers are damaged in a specific area of the cerebellum, a part of the brain largely devoted to regulating muscular activity
What is the treatment for Shivers in horses?
- No specific treatment, but It has been suggested that dietary treatment of affected draft horses with a high-fat, low carbohydrate feed may be beneficial if instituted early in the course of the disease.
