Equine neurology, toxicology, myopathy Flashcards

1
Q

Which viruses have a primary neurotropism in horses? Which arbo viruses are associated with CNS disease in horses? Which cause neuropathy by damaging BBB?

A
Viruses with primary neurotropism:
- Rabies
- Borna virus
Arbo viruses: 
- Eastern, Western and Venezuelan equine encephalitis
- Japanese encephalitis
- West Nile virus
Damage BBB:
- EHV-1, 4
- Equine Infectious Anaemia (EIA)
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2
Q

How are neurological viral diseases diagnosed in horses? Normal findings?

A

History:
- geographical location
- recent travel
- onset and duration
- other horses
- vaccination history
Clinical examination:
- fever
- normally symmetrical, multifocal or diffuse lesions
CSF analysis and serology:
- most commonly mononuclear pleocytosis and increased protein concentration
- culture, PCR, ELISA, IFAT to identify Ag or Ab
Medical imaging and functional testing:
- CT/MRI: usually non specific intracranial oedema
PM examination:
- Histopath: usually immunohistochemistry and/or PCT amplification necessary

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3
Q

Treatment for neurological viral diseases in horses?

A

Isolate (because fever + neurological signs = infectious unless proven otherwise!)
Quiet, dark stable with deep bedding and padded walls
Turn recumbent horses every 4-6 hours
Sling?
NSAIDs
Corticosteroids?
Antiviral therapy: acyclovir, valacyclovir
Ag-specific therapy: WNV
Vitamin E, thiamine

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4
Q

What do the different Equine Herpes viruses cause?

A
EHV-1: respiratory, abortion, myeloencephalopathy
EHV-2: keratitis
EHV-3: coital exanthema
EHV-4: respiratory
EHV-5: multi nodular pulmonary fibrosis
EHV-6 to 8: donkeys
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5
Q

EHV-1: features of the virus?

A
Alpha herpes virus
Specific to horses
Enveloped capsid containing DNA genome
Latent infections
Humoral immunity is very short lived
Naturally low Ab level
May occur sporadically or as outbreaks
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6
Q

EHV-1 pathogenesis? Neurological signs?

A

Vasculitis and thrombosis of arterioles in brain and spinal cord (viral endotheliotropism)
May or may not show prior respiratory signs or fever
May be recent history of respiratory disease or abortion in the premises
Sudden onset and early stabilisation of signs
Signs:
- ataxia in hindlimb or all 4, or recumbent
- cauda equina signs: atony of bladder, flaccid tail and anus, perineal hypoalgesia
- occasionally show cranial nerve involvement

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7
Q

Diagnosis of EHV-1?

A
Virus isolation/PCR:
- Nasal swab
- Buffy coat
- CSF
Serology:
- Complement fixation, ELISA
- 4 fold rise in titre or >1:80
CSF: xanthochromia
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8
Q

Management of neurological EHV-1? Prevention?

A

Isolate
Prognosis reasonable with good nursing care
- better if nor recumbent
- recovery days-weeks (up to 1 year)
- poor prognosis if recumbent >24h
Recurrence of neurological signs not reported
Vasculitis: NSAIDs, corticosteroids, aspirin (anti-thrombotic)
Prevention: vaccination for EHV-1 and 4 (but ineffective against neurological form and possibly worsens case if given during neurological outbreak)

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9
Q

Rabies: Type of virus? Transmission? Pathogenesis?

A

Lyssavirus
Rhabdovirus family
Neurotrophic
Transmitted by saliva contaminated bite wounds
Uncommon in horses
Pathogenesis:
- Local inoculation at wound site
- Access to peripheral nerve
- Gradual movement centrally
- Replication in spinal/dorsal root ganglia
- Rapid spread in CNS (cord, brain, sympathetic trunk)
- Centrifugal spread down nerves (salivary glands)
- Incubation period very variable: 9 days - 1 year (depends on strain, host species, inoculum, proximity of inoculation to CNS)

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10
Q

Signs of rabies in horses?

A

No pathognomonic signs
From mild hindlimb lameness to sudden death
Signs depend on euro-anatomic location of pathology

Forms:
Spinal -> paralytic form:
- most common
- localised hyperaesthesia: self mutilation of extremity/site of inoculation
- progressive ascending: ataxia, weakness, lameness
- recumbent 3-5 days
Brain stem -> dumb form:
- unusual in horses
- depression
- anorexia
- head tilt, circling
- ataxia
- dementia/blindness
- salivation/dysphagia
- tail/penis/bladder paralysis
- self-mutilation
Cerebrum -> furious form:
- unusual in horses
- photophobia/hydrophobia
- aggression/bizarre behaviout
- hyperaesthesia
- tenesmus
- muscle tremors
- seizures
Forms can co-exist or progress
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11
Q

Rabies PM exam in horses?

A

Histology: eusinophilic inclusion bodies (Negri bodies) within neurones
Fluorescent Ab

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12
Q

Arbovirus groups A, B and C?

A
Arbovirus Group A: Togaviridae:
- EEE, WEE, VEE
Arbovirus Group B: Flaviviridae:
- WNV: Hapanese encephalitis
Arbovirus Group C: Bunyaviridae:
- limited reports of infection in horses
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13
Q

Limitations to a neuro exam in horses?

A

Size
Behaviour/danger
Recumbency

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14
Q

Neuro exam in a horse?

A
From a distance:
- Mentation
- Behaviour
- Posture
Cranial nerves
Observe and palpate neck and back:
- muscle atrophy, asymmetry, sweating
- range of movement
- cervicofacial reflex
- cutaneous trunci (panniculus) reflex)
Tail: voluntary movement, tone
Perineal reflex, tail clamp, anal tone
Males: external genitalia
Rectal exam: assess lumbar, sacral or coccygeal vertebrae, bladder volume and tone
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15
Q

What is cranial nerve I? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A

Olfactory nerve
Function: olfaction
Dysfunction: reduced or absent smell
Evaluation: difficult and subjective

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16
Q

What is cranial nerve II? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A
Optic nerve
Function: vision
Dysfunction: partial or complete blindness (dilated, unresponsive pupils)
Evaluation: 
- vision (obstacles)
- menace response (>2wks)
- PLR
- visual placing
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17
Q

What is cranial nerve III? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A
Oculomotor nerve
Function: 
- pupil size
- eyelid movement (ispilateral dorsal, ventral and medial recti, ventral oblique, elevator palpebrae)
Dysfunction:
- ventrolateral strabismus
- inability to rotate eye dorsally, ventrally and medially
- dilated unresponsive pupil
- ptosis of upper lid
Evaluation: 
- PLR
- physiological nystagmus
- eye position at rest
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18
Q

What is cranial nerve IV? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A

Trochlear nerve
Function: contralateral dorsal oblique muscle
Dysfunction: dorsolateral strabismus (fundic examination)
Evaluation:
- physiological nystagmus
- eye position at rest

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19
Q

What is cranial nerve V? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A

Trigeminal nerve
Function:
- sensory innervation of face
- motor innervation to masticatory muscles
Dysfunction:
- masticatory muscle atrophy and jaw weakness (dropped jaw if bilateral)
- facial hypo/anaesthesia
- neurotropic keratitis
Evaluation:
- size and symmetry of masticatory muscles
- sensory function (corneal, palpebral, nasal)

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20
Q

What is cranial nerve VI? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A
Abducens nerve
Function: ipsilateral lateral rectus and retractor bulbi muscles
Dysfunction: 
- medial strabismus
- inability to move eye laterally and to retract eyeball
Evaluation: 
- physiological nystagmus
- eye position at rest
- corneal reflex
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21
Q

What is cranial nerve VII? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A
Facial nerve
Function: 
- motor to facial muscles
- taste for rostral 2/3 of tongue
- lacrimal gland
Dysfunction: 
- drooping
- inability to move ear and lip
- absent blink
- KCC
Evaluation: 
- facial symmetry
- palpebral reflex
- menace response
- corneal reflex
- STT
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22
Q

What is cranial nerve VIII? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A
Vestibulocochlear nerve
Function: 
- hearing
- vestibular function
Dysfunction: 
- partial or complete deafness
- signs of vestibular disease
Evaluation: 
- BAER
- signs of vestibular disease: head posture, physiological nystagmus, gait, blindfold
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23
Q

What is cranial nerve IX? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A
Glossopharyngeal nerve
Function: 
- motor to pharynx and palate?
- sensory to caudal 1/3 of tongue and pharynx
- salivary glands
Dysfunction: 
- dysphagia
- absent gag
Evaluation: 
- gag
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24
Q

What is cranial nerve X? What is its function? What is seen with dysfunction? How can you evaluate it in horses?

A
Vagus nerve
Function: 
- larynx, pharynx and oesophagus
- all thoracic and abdominal viscera
Dysfunction: 
- dysphagia
- inspiratory dyspnoea
- dysphonia
- regurgitation
- absent gag
Evaluation: 
- gag
- oculocardiac
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25
What is cranial nerve XI? What is its function? What is seen with dysfunction?
``` Accessory nerve Function: - trapezius - part of sternocephalicus Dysfunction: trapezius atrophy ```
26
What is cranial nerve XII? What is its function? What is seen with dysfunction? Evaluation?
``` Hypoglossus nerve Function: motor to tongue Dysfunction: - tongue deviation/atrophy - problems with prehension Evaluation: - tongue size, tone and symmetry ```
27
Possible causes of an abnormal posture in horses?
Orthopaedic problem Neurological: 1. Loss of spatial awareness - conscious proprioceptive deficits at rest, abnormal posture when stop/not correcting (don't manipulate limb) 2. inability to move limb
28
Define ataxia? What to look for?
Subconscious proprioceptive deficits seen as irregular and unpredictable movement Lood for poor coordination, swaying, limb moving excessively during swing phase (weaving, abduction, adduction, crossing limbs, stepping on self) Exaggerated by tight circles, sudden stopping, backing, hills, raising head
29
Types of ataxia in horses?
``` Cerebellar: - no weakness - hypermetric ataxia - other signs of cerebellar disease e.g. tremor, lack of menace response Vestibular: - loss of balance - hypometric ataxia - wide based - other vestibular signs e.g. head tilt, nystagmus Spinal (most common in uk): - dysmetric ataxia - +/- weakness ```
30
Classification of ataxia severity?
Subtle: deficits barely detected at normal gait, occur during backing, stopping, turning, swaying, neck extension etc Mild: detected at normal gait, exaggerated by above manoeuvres Moderate: prominent at normal gait, tend to buckle and fall with above manoeuvres Severe: tripping and falling spontaneously at normal gait to complete paralysis
31
What neurological problem causes weakness in horses?
``` Interruption to general somatic efferent pathways (motor pathways) Extensor weakness: - sinking/buckling - weak when pulling tail Flexor weakness: - toe drag/delay in picking up - swinging movement ``` ``` Motor tract lesion (UMN): tail pull during movement Motor neuron (LMN): tail pull at rest ```
32
West Nile Virus: Epidemiology? Pathogenesis? Signs?
Epidemiology: - replicates in birds = reservoir - mosquitoes (Culex) transfer virus from birds to a number of species (horses and humans) - human and horses are terminal hosts Pathogenesis: 1. Initial virus replication at site of inoculation 2. Viraemia -> signs of uncomplicated infection (fever, depression, anorexia) 3. In some horses virus enters CNS: - diffuse or multifocal encephalomyelitis - involvement of spinal cord common (unlike EEE / WEE) Neurological signs: - muscle fasciculations over entire body (particularly head and neck) - weakness, ataxia, dysmetria - cranial nerves may be affected - mentation may be affected (indirectly due to intracranial oedema) - sudden death in some horses Treatment: - hyperimmune plasma specific to WNV available in USA - supportive care - NSAIDs - DMSO? Mannitol? to reduce oedema - corticosteroids? Prognosis: - few cases gradually resolve -> long term neurological deficits
33
What plants are poisonous to horses?
``` Wild: - Ragwort - Giant hogweed - Water hemlock - Foxglove (Digitalis) - Deadly nightshade - Bracken fern - Oak/acorn - Rhododendron - Houndstongue Garden: - Sorghum - Oleander - Lantana Fungal/toxin elaboration: - Endophytes e.g. ryegrass, fescue toxicoses - Contamination e.g. mouldy corn ```
34
Which poisonous plants are hepatotoxins? What are the toxins?
Ragwort - pyrollizidine alkaloid Houndstongue - pyrollizidine alkaloid Lantana - triterpene acids, lantadene A, lantadene B
35
Ragwort: Name? Which stages toxic? Pattern of growth? When ingested? Toxicology?
= Senecio jacobaea Toxic at all stages of growth and when dried Biennial: - spring: Small rosettes (commonly ingested) - summer: up to 1.5m tall with distinctive yellow flowers and ragged leaves (rarely ingested except in preserved forage) Unpalatable when fresh - usually ingested in preserved state Toxicology: - hepatotoxic pyrrolizidine alkaloids or triterpene acids cause liver failure - pyrrolizidine alkaloids alkalate DNA, stop hepatocyte cell division, causing megalocytosis and liver failure
36
Clinical signs of liver failure from ragwort?
``` Weight loss Jaundice Dullness and depression Muscle tremors and weakness Frequent yawning Inappetance and difficulty swallowing Respiratory noise/laryngeal paralysis Compulsive walking/incoordination/head pressing Photosensitisation Colic Encephalopathic signs: classic signs are quiet, dull, head press ```
37
Diagnosis of ragwort poisoning?
``` Examine hay for ragwort leaves Clinical signs Test blod: - non specific signs of liver damage - specific alkaloid detection (definitive) PM ```
38
Methods of control of ragwort?
Spraying herbicide (blanket or spot): - cannot use land for grazing for weeks to months - leaves bare patches where ragwort can easily re-establish Uprooting and burning (manual or mechanical): - labour intensive - wear gloves to prevent skin irritation Cutting: - less effective as roots remain and can re-establish - only done when field not in use to prevent flowering, seeding and spreading - ensure cuttings removed ?Grazing land with sheep which may be resistant to toxicity before turning horses out: - controversial
39
Which poisonous plants are myotoxins an enterotoxins? What are the toxins?
Myotoxins: - sycamore: hypoglycin A Enterotoxins: - oak/acorns: tannins
40
Sycamore poisoning: Toxicology? Clinical signs? PM?
Toxicology: - hypoglycin A? - acquired multiple Acyl-CoA dehydrogenase deficiency - causes atypical myopathy Clinical signs: - weakness, fasciculations - recumbency - red urine (myoglobinuria) - marked elevations in serum muscle enzymes (CK, AST) PM: widespread myonecrosis (skeletal and cardiac) Spring and autumn - sudden weather change? - horses at pasture
41
Acorn/oak poisoning: Toxicology? When ingested? Pathology? Clinical signs? Diagnosis? Treatment? Control?
Toxicology: - oak leaves and acorns contain tannins - highest tannin content of sap in spring Acorns Sept-Oct Pathology: - gastroenteritis - haemorrhages in abdominal cavity over GIT and beneath endo and epicardium - subcutaneous oedema over pelvic limbs and along ventral body wall Clinical signs: - parachute/acute/sudden death - colic - tenesmus - haemorrhagic diarrhoea But poisoning rare in horses - some unaffected Diagnosis: - acorn husks/shells in faeces - urinary phenolic content to differentiate from other colics Treatment: - as medical colic (IVFT, analgesia, oral laxatives, diuresis, acid/base balance, serum calcium levels) Control: - fence off oak trees in autumn when acorns are abundant - pick up acorns from pasture
42
What poisonous plants are cardio-respiratory toxins? Toxin?
Oleander Rhododendron Fox glove Contain cardenolides or cardiac glycosides which interfere with electrical conductivity of the heart -> arrhythmias/sudden death
43
Oleander: Which parts toxic? Toxin? Signs? Necropsy?
``` All parts very toxin Cardiac glycosides Signs: - Diarrhoea/melaena - Disruptive cardiac arrythmias - Death often within minutes Necropsy: - Nil findings - Plant? ```
44
Which poisonous plants are dermotoxins?
St John's Wort | Giant Hogweed
45
St John's Wort: Where found? Growth? What does it cause?
Hedgerows and gardens Slow expansion, perennial Primary photosensitisation Hypericin - therapeutic agent?
46
Giant Hogweed: What does it cause?
No specific signs | Oral irritation/ulcers
47
Which poisonous plants are neurotoxins?
``` Deadly nightshade Yew Hemlock Sorghum Flatweed Singletary Pea Ryegrass Mouldy corn ```
48
Sorghum: What is it? Toxin? What does it cause?
'Milo'/'Sudan' grass Chronic cyanide poisoning? - cyanogenic glycosides Bladder paralysis
49
Flatweed: Where found? What does it cause?
``` Common wild plant in stable yards and poorly maintained pastures (dandelions) Widespread Ingested in low amounts normally Stringhalt (but not really in UK) Persistent neurologic deficits ```
50
Deadly nightshade: Signs of poisoning? Treatment?
``` Atropine related signs (parasympatholytic): - mydriasis - shivering/muscle spasms - tachycardia - dry mucous membranes - colic (ileus/obstipation) Treatment: - neostigmine? (but may be worse than the poisoning!) - activated charcoal - fluids etc ```
51
Bracken fern: How bad/common? Toxicology? Clinical signs? Diagnosis? Treatment? Prognosis?
Overstated effects - heavy/persistent ingestion? Not very common Contains thiaminase -> vitamin B1 (thiamine) deficiency Carcinogenic? Clinical signs (bracken staggers): - anorexia - cardiac dysrhythmia - crouched stance, arched neck, feet wide apart - incoordination - convulsions - clonic spasms and opisthotonus then death Diagnosis: - low blood thiamine (not pathognomonic) - elevated pyruvate - bracken on pasture or in hay - known ingestion Treatment: - thiamine every 12h IM or slow IV for up to 7 days - avoid IV if possible (anaphylactic reaction) Prognosis: - therapy usually highly effective if early
52
Mare's tails poisoning: Pathogenesis? Signs? Treatment?
Thiaminase CNS signs predominate Treatment: thiamine
53
Hemlock and water hemlock: What do the plants look like? Toxicology? Which parts of plant toxic? When? Clinical signs? Treatment?
Flowers/leaves similar to cow parsley Distinct irregular purple blotches on stem Hemlock flowers and fruits contain most toxic alkaloid Water hemlock roots and leaves Especially poisonous in dry, hot summers Toxicology: - hemlock: alkaloid coiine (nicotine like action) - water hemlock: cicutoxin and cicutol - first stimulating and then depressing autonomic ganglia - curare-like effect - paralysing skeletal muscle motor nerve endings Clinical signs: - agitation, nervousness - twitching - seizures - excess salivation - dilated pupils - skeletal muscle weakness - cardiac abnormalities - difficulty breathing - death from respiratory paralysis May develop following ingestion of only small quantities Treatment: activated charcoal and/or lavage
54
Yew: Where found? Toxicology? Which parts poisonous? Pathology? Clinical signs?
``` Evergreen - hedges and gardens Toxicology: - alkaloid taxines - all parts of tree poisonous Pathology: - distended stomach - inflammation if death occurs after several hours - liver, spleen and lungs engorged with dark blood Clinical signs: - trembling - ataxia - bradycardia - hypothermia - weak - dyspnoea - rapid death ```
55
What are the main feed-borne mycotoxins that affect horses?
Mouldy corn toxicity Rye grass staggers Fescue toxicosis
56
Mouldy corn poisoning: Toxin? Pathology? Signs?
``` Mycotoxin = fumonisin B1 Infected corn/commercial foods Can be fatal to horses Pathology: liquefactive necrosis of brain Signs 2-4 weeks after ingestion: - anorexia - blindness - ataxia - head pressing - circling - hyperexcitability - seizures - recumbency/death ```
57
Ergot/rye grass staggers: Toxin? Signs? Treatment?
Associated with endophyte infected plant - produces toxin Lolitrem B Signs: - trembling, unsteadiness and poor muscle coordination - erratic and anxious behaviour - milder cases may display some trembling of head, neck, shoulders - signs worsen if exposure increases Treatment: - get better quickly if take off pasture
58
Fescue toxicosis: Features of plant?Toxicology? Which horses affected? Clinical signs?
``` Perennial tufted grass, related to ryegrass 10cm - 2m tall Toxicology: - toxicity due to endophyte Acremonium coenophialum - most significant alkaloid substance produced is the ergo peptide ergovaline Affects pregnant mares and unborn foals Clinical signs: poor reproductive function: - prolonged gestation - abortion - premature separation of chorion - dystocia - thickened and retained placenta - lack of milk let down - reduced pregnancy rates - immature foals born - poor foal immunity ```
59
Aflatoxins: Which plants? Which toxins? Where? Clinical signs? Treatment? Management?
``` Aspergillus 5 major toxins: - B1, B2, G1, G2, M1 - B1 most important Mostly stored feeds Poorly recognised clinically Clinical signs: 1. Sudden death: - no premonitory signs 2. Neurotoxic syndrome: - incoordination, aimless walking - lethargy -> mania, convulsions - delirium - sweating - death 3. Hepatotoxic syndrome: - head swelling, jaundice - depression, signs of liver failure - coma -> death No effective treatment Management: - remove contaminated feed - supportive therapy - high dose vitamin B - vitamin B1? - sedation if required - mannitol/DMSO - laxatives/activated charcoal? ```
60
Blue-green algae: Where? Toxicology?
Natural water courses - looks like algae but isn't Cyanobacteria Highly toxic
61
Bran disease: Cause? What does it cause?
Ca/Po4 imbalance | Secondary nutritional hyperparathyroidism
62
Lead poisoning: Clinical signs?
``` Peripheral nerve dysfunction: - motor nerves worse -> weakness - minimal sensory loss Depression Weight loss Laryngeal/pharyngeal paralysis -> dysphagia, aspiration pneumonia Facial paralysis Anal/bladder paralysis Colic Diarrhoea Hepatic failure Blindness Seizures Coma -> death Lead crosses placenta: - premature/weak/still born foals ``` (can look like rabies or botulism)
63
Treatment of lead poisoning in horses?
``` Remove source Chelation therapy Ca disodium EDTA - binds out bone lead Fluids Nursing support High dietary calcium ```
64
Selenium poisoning: How happens? Signs?
``` Supplement overdose - care with cattle licks as horses need less selenium per day than ruminants Seleniferous plants Signs: - hair loss (mane, tail) - laminitis ```
65
Monensin poisoning: When seen? Signs?
Chicken feed often contains monensin (coccidiostat for poultry but highly toxic to horses) Acute - sudden death, diarrhoea Chronic - cardiac failure DCM
66
Glycogen branch enzyme (GBE) deficiency: How does it present? Diagnosis?
Foal dies suddenly Poor body condition Muscle biopsy - PAS staining unusually absent
67
Polysaccharide storage myopathy: Why happens? Presentation? Diagnosis? Treatment?
Pathogenesis: - accumulation of glycogen = storage disease on exercise Poor performance Becomes stiff and reluctant to move after short period of exercise Raised muscle enzymes Semimembranosus muscle biopsy – abnormal accumulation of PAS positive material and evidence of cell degeneration/regeneration, amylase resistant inclusion bodies Treatment: low carb, high fibre diet (oil to replace carbs for energy)
68
Chronic exertional rhabdomyolysis: How does it present? Diagnosis?
Stress Intermittent muscle cramping and stiffness Poor performance Mild elevation of CK and aspartate aminotransferase Muscle biopsy – cellular degeneration/regeneration but normal PAS staining
69
Hyperkalaemic periodic paralysis (HPP): How does it present?
``` Well muscled (Sire impressive) Periods of sweating and muscle fasciculations over shoulder, flank and neck Lasts 30 minutes and is weak Seems to happen when excited or stressed ```
70
Treatment for acute and chronic exertional rhabdomyolysis?
Acute: pain relief, fluids, ACP Chronic: warm up, avoid stress and high energy feeds