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LA DX & TX II > Exam 1 - Equine Myopathies > Flashcards

Exam 1 - Equine Myopathies Flashcards

1
Q

what is a myopathy? what does it cause in horses?

A

dysfunction of the muscle fiber

poor performance, exercise intolerance, weakness/stiffness, & rhabdomyolysis

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2
Q

when working up a horse with a suspected myopathy, why are CK & AST useful values?

A

CK - evaluates for muscle damage

AST - evaluates the horse for any hepatic damage, 1/2 life of 8-10 days, always measure a CK alongside an AST to rule out concurrent muscle injury

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3
Q

what are the differences between exertional & non-exertional rhabdomyolysis?

A

exertional - seen in a horse usually concurrent with exercise, from exertion

non-exertional - many causes but not related to the animal moving/exercising, caused by sources other than exertion, including genetics and can be triggered by stress, reactions to certain vaccines and infections (particularly streptococcus), and a poor diet

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4
Q

why are NSAIDS contraindicated in severe cases of tying up?

A

in rhabdomyolysis - there is myoglobinuria from the muscle damage causing acute kidney injury

NSAIDS are nephrotoxic alone - so very concerning for an animal who’s kidneys are already compromised

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5
Q

what is the mode of inheritance of PSSM?

A

type 1 - autosomal dominant inheritance

mutation in the glycogen synthase 1 gene

type 2 - unknown

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6
Q

what is the mode of inheritance of HYPP?

A

autosomal dominant - point mutation in the SCN4A gene

mutation in the Na channel gene that controls muscle contraction

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7
Q

what is the mode of inheritance of IMM?

A

usually a complication from a primary infectious disease with an autoimmune response affecting skeletal muscle

genetic mutation of the myosin heavy chain 1 - myosin heavy chain 1 myopathy

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8
Q

what are the similarities between PSSM & HYPP?

A

both are autosomal dominant genetic inherited conditions

both can be induced by triggers - diets high in CHO/NSC for PSSM & diets high in K+ for HYPP

both majorly affect quarter horses

clinical signs - both cause the horse to not want to move around much

both can be diagnosed on the AGHA 6 panel/muscle biopsy

similar management plan - avoid long periods of rest, diet changes, daily turnout

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9
Q

what are the differences between PSSM & HYPP?

A

HYPP - non-exertional myopathy!!

clinical signs of HYPP look more like colic/tetanus horse

different treatment needed for HYPP because you need to drive potassium into cells

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10
Q

what is calciphylaxis?

A

calcium accumulates in the small blood vessels of fat & skin tissue, animal will have a high Ca:P ratio

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11
Q

what medication & route of administration has been implicated the most in the development of clostridial myonecrosis?

A

banamine given IM

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12
Q

what is the most important therapy for a horse with clostridial myonecrosis?

A

oxygen therapy

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13
Q

what type of tree has been associated with atypical myopathy?

A

box elder tree

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14
Q

what is the pathophysiology of equine motor neuron disease? how does it relate to the clinical signs appreciated?

A

horses deficient in vitamin E for more than 18 months

deterioration of lower motor neurons from lack of vitamin E, (the nerves that supply the direct neurological input into all muscles) muscles atrophy, resulting in the clinical signs of weakness and weight loss characteristic of this disease

condition affects the neck (cervico-thoracic) and back (lumbar-sacral) areas of the spinal cord - clinical signs such as low head carriage & raised tail head, elephant on a ball stance, & shift weight lameness/recumbency

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15
Q

what clin path values are you paying special attention to in a horse you suspect has some sort of myopathy going on?

A

CK & AST

renal values

urinalysis - look for myoglobinuria

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16
Q

what are the 2 chronic exertional myopathies that are genetically inherited?

A

recurrent exertional rhabdomyolysis & polysaccharide storage myopathy

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17
Q

what are the 2 types of exertional myopathy?

A

sporadic & chronic

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18
Q

what are the types of non-exertional myopathies covered in this lecture?

A

circulatory, myotonic, inflammatory/infectious, traumatic, nutritional/toxic, & misc

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19
Q

what are some other common names for exertional rhabdomyolysis?

A

tying up

monday morning sickness

azoturia

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20
Q

what is the clinical presentation that is commonly seen in a horse with exertional rhabdomyolysis?

A

onset of signs occurs shortly after the beginning of exercise

firm & painful muscles & tremors - lumbosacral region & gluteal muscles

excessive sweating, tachycardia/tachypnea, reluctance/refusal to move, elevated CK (>10,000-100,000)

myoglobinuria & AKI

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21
Q

how is a horse with exertional rhabdomyolysis treated?

A

stall rest & diuresis - electrolyte & fluid correction

pain relief - judicious use of NSAIDS/nephrotoxic drugs - can use ace/torb/methocarbamol

give vitamin E

gradual return to exercise

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22
Q

what is recurrent exertional rhabdomyolysis?

A

intermittent form of tying up in horses due to an abnormality in intracellular calcium regulation with no specific diagnostic test

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23
Q

what horses are commonly affected by RER (risk factors)?

A

thoroughbreds age 2 YEARS!!! to 3 years old

fillies affected

anxious/nervous temperament

lame horses

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24
Q

what are the risk factors pertaining to diet & exercise intensity for horses & RER?

A

high grain diets

racehorses/gallop training, 3 day eventers/cross country, & trotters after 15 minutes

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25
Q

how is stress managed for RER horses?

A

stall positioned in a quiet area of the barn

train them first thing

turn out often

avoid excitable/frustrating training regimes (holding back)

attention to & treatment of lameness

avoid stall rest or lay-up if possible

dantrolene before exercise

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26
Q

why does PSSM cause a myopathy?

A

unregulated synthesis of glycogen which results in excessive sugar in the muscle cells

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27
Q

what horses are commonly affected by type I PSSM?

A

quarter horses - halter horses

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28
Q

what horses are commonly affected by type II PSSM?

A

quarter horses, drafts, & warm bloods

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29
Q

what triggers are associated with PSSM?

A

diets high in CHO/NSC/starch (sweet feed, corn, wheat, oats, barley, molasses) & prolonged periods of rest

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30
Q

what clinical signs are seen with both types of PSSM?

A

muscle pain & stiffness - exertional

sweating, shifting lameness, exercise intolerance, reluctance to move, weakness, & pigmenturia

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31
Q

what clinical signs are seen in quarter horses with PSSM?

A

early onset & persistent high CK

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32
Q

what clinical signs are seen in draft breeds with PSSM?

A

middle age onset - belgians & percherons

trembling & muscle atrophy

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33
Q

what clinical signs are seen in warm bloods with PSSM?

A

back soreness & poor performance

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34
Q

what sample is needed for an AQHA 6 panel? what does an AQHA 6 panel test for?

A

hair sample or whole blood

PSSM, HYPP, malignant hyperthermia, GBED, HERDA, & IMM

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35
Q

T/F: CK rapidly rises - 4 to 6 hours & AST takes a couple of days

A

true

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36
Q

how is PSSM type I diagnosed?

A

a sample of hair or EDTA whole blood to test for the GYS1 mutation

muscle biopsy - abnormal amylase resistant polysaccharide

exercise trial - watch CK & AST to evaluate for muscle damage

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37
Q

T/F: exertional rhabdomyolysis - episodes usually happen concurrent with exercise (sporadic) & chronic/intermittent are more likely to be related to genetic disorders

A

true

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38
Q

how is PSSM type II diagnosed?

A

no genetic test - need to do a muscle biopsy &
exercise trial

exercise trial - take a baseline CK & then exercise the horse, & take a measurement hours later, an 4 fold increase from the baseline is consistent with type II PSSM

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39
Q

what would you expect to see on a muscle biopsy of a horse with type II PSSM?

A

abnormal aggregation of glycogen in the muscle

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40
Q

whats the recommended procedure for obtaining a muscle biopsy in a horse with a suspected myopathy?

A

inject 5-10ml of lidocaine sq around the muscle

incision made through the skin & sq tissues about 2 inches long

parallel 1 inch incisions are made about 1/2 inch apart from each other & held in place with forceps while the muscle is transected dorsally & ventrally - sample will contract to form 1/2 inch cube

close with simple interrupted sutures or staples

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41
Q

what diet recommendations are made for managing horses with PSSM?

A

grazing muzzle, low NSCs, give a hay with <12% NSC, manage BCS (overweight/effects on insulin), ration balancer, & supply a potential fat source for energy

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42
Q

what management is recommended for horses with PSSM?

A

avoid long periods of rest

gradual re-introduction to exercise

daily turnout

5+ days/week of moderate exercise (30 minutes)

fasting for 6 hours prior to exercise

diet changes

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43
Q

how is RER diagnosed?

A

the horse has to have more than 1 episode of tying up

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44
Q

what is an example of a non-exertional rhabdomyolysis with a genetic cause?

A

HYPP

45
Q

what is an example of a non-exertional rhabdomyolysis that has a circulatory cause?

A

post-anesthetic myopathy

46
Q

what are some risk factors associated with post-anesthetic myopathy?

A

large breeds (drafts)

prolonged recumbency

positioning of the animal underneath anesthesia

animal is on a hard surface

genetics - malignant hyperthermia

47
Q

what is the pathogenesis of localized post-anesthetic myopathy?

A

increased weight = increased compression

leads to decreased perfusion, decreased nerve function, & hypotension

48
Q

T/F: in a horse with generalized post-anesthetic myopathy, prognosis is poor if the animal develops signs while still under anesthesia

A

true

49
Q

what is the suggested pathogenesis of generalized post-anesthetic myopathy?

A

unknown - it is poorly understood but may be related to malignant hyperthermia

50
Q

what are the clinical signs seen with localized post-anesthetic myopathy?

A

signs occur in recovery/few hours after anesthesia

peripheral neuropathy, hot/swollen/painful muscles, recumbency, & colic

51
Q

what are the clinical signs seen with generalized post-anesthetic myopathy in a horse under anesthesia?

A

hyperthermia, muscle contractions, & respiratory acidosis

52
Q

what are the clinical signs seen with generalized post-anesthetic myopathy in a horse recovering from anesthesia?

A

anxiety, tachycardia/tachypnea, sweating, recumbency

53
Q

what treatment is recommended for horses with post-anesthestic myopathy?

A

similar to exertional rhabdomyolysis - muscle relaxants (guaifenesin, dantrolene especially in malignant hyperthermia horses for the Ca2 channels, & methocarbamol)

bicarb for acidosis

vitamin E

may need to use a sling in severe cases

54
Q

what is the name of the horse that we trace HYPP back to?

A

impressive - big body/little head/ears/little feet

55
Q

T/F: 1.5% of all quarter horses have HYPP genes

A

true

56
Q

T/F: up to 56% of all halter horses have HYPP genes

A

true

57
Q

what are some triggers associated with HYPP attacks?

A

diet changes, fasting, GA, concurrent illness, exercise restriction

58
Q

T/F: severity of HYPP attacks depends on homozygous/heterozygous genotype

A

true

59
Q

why is HYPP not truly tying up even though the clinical signs appear to be similar?

A

their muscle enzymes are generally normal

60
Q

what is the most common cause of hyperkalemia on a serum chemistry in the horse?

a. diarrhea
b. hypp
c. spurious lab error due to sample handling
d. addison’s disease

A

c. spurious lab error due to sample handling

61
Q

what clinical signs are seen with HYPP attacks?

A

may look like colic

muscle tremors, prolapsed 3rd eyelid, inspiratory stridor, agitation, paralysis, collapse, & death

62
Q

what major clin path abnormality is seen in horses with HYPP?

A

elevated K+ on the chemistry

63
Q

T/F: GBED affects foals & is a fatal disease killing them by 6-8 weeks of age

A

true

64
Q

what is the recommended treatment for HYPP?

A

want to get K+ back into the cells & protect the heart, dextrose

mild cases - karo syrup orally

severe cases - IVFT with dextrose, also give calcium & bicarbonate (protect the heart)

insulin

acetazolamide - diuretic, carbonic anhydrase inhibitor

hydrochlorthiazide

65
Q

what feed should be avoided for horses with HYPP?

A

feed high in K+ - alfalfa, brome hay, canola oil, soybean meal or oil, & molasses

66
Q

what feed should be given to horses with HYPP?

A

timothy/bermuda grass hay, oats, corn, wheat, barley, & beet pulp

feed several times a day

67
Q

what management is recommended for horses with HYPP

A

diet change

exercise routine

frequent access to a large paddock

acetazolamide

karo syrup on hand prior to stressful events

68
Q

T/F: all PSSM type II horses have myofibrillar myopathy

A

false

69
Q

what horses are commonly associated with having myofibrillar myopathy?

A

arabians & warm bloods - previously diagnosed with PSSM type II

70
Q

how is myofibrillar myopathy diagnosed?

A

muscle biopsy with a special stain for desmin

71
Q

which is more commonly seen, localized or generalized post-anesthetic myopathy?

A

localized

72
Q

T/F: the signs of myofibrillar myopathy are the same as the human disorder

A

false

73
Q

what clinical signs are seen in endurance horses with myofibrillar myopathy?

A

marked muscle stiffness 5 miles into ride

milder signs of RER, elevated CK & AST not consistent, & decreased performance at 8 years of age

74
Q

what would you expect to see on a muscle biopsy of a horse with myofibrillar myopathy?

A

abnormal red clumping of desmin in scattered muscle fibers

75
Q

what are the major agents involved in bacterial causes of inflammatory/infectious myopathies? what are 2 less common?

A

streptococcal & clostridial

borrelia burgdorferi (lyme) & anaplasma phagocytophilia

76
Q

what are the major agents involved in viral causes of inflammatory/infectious myopathies?

A

EIV & EHV

77
Q

what are the major agents involved in parasitic causes of inflammatory/infectious myopathies?

A

sarcocystis fayeri & trichenella spiralis

78
Q

what is the pathogenesis of immune mediated myositis?

A

usually a complication of a primary infectious disease - usually strep equi or vaccine

body has an autoimmune response affecting skeletal muscle

79
Q

what genetic mutation is seen in immune mediated myositis? what horses are affected by it?

A

myosin heavy chain 1 myopathy

7% of quarter horses

also affects reining/working cow horses & halter horses

80
Q

what myopathy can progress to calciphylaxis?

A

immune mediated myositis

81
Q

T/F: if a horse with immune mediated myositis develops calciphylaxis, it usually becomes a fatal disease

A

true

82
Q

what are the clinical signs seen in horses with immune mediated myositis?

A

rapid (1-3 days) loss of muscle mass that is usually symmetrical affecting the epaxial & gluteal muscles the most

lethargic, anorexia, stiffness, difficulty standing

can progress to calciphylaxis

83
Q

how is immune mediated myositis diagnosed?

A

history, clinical signs, genetic test for MYH1, watch their Ca:P ratio, & muscle biopsy

84
Q

what is seen on muscle biopsy of a horse with immune mediated myositis?

A

extensive lymphocytic infiltration & mononuclear vasculitis with regenerative & atrophied myofibers

85
Q

what is the prognosis of immune mediated myositis?

A

unless it progresses to calciphylaxis, good prognosis

muscle atrophy should stop

in 2-3 months, muscle mass should return

relapse is possible

86
Q

what is the recommended treatment for immune mediated myositis?

A

corticosteroids for 1 month - appetite should improve 48 hours after starting steroids

diet - high in protein/amino acids

DO NOT GIVE STRANGLES VACCINE

87
Q

what clostridial species has the highest mortality rate in horses with clostridial myonecrosis?

A

clostridium perfringens type a

88
Q

what are the risks associated with clostridial myonecrosis?

A

puncture wound

injection - banamine or vaccine

89
Q

what is the pathogenesis of clostridial myonecrosis?

A

spores germinate in the wounds & exotoxins are produced causing necrosis, hemolysis, & thrombosis

90
Q

what are the clinical signs of clostridial myonecrosis?

A

rapid death, edema/local swelling, pain, fever, tachycardia/tachypnea, endotoxemia, & crepitus

91
Q

what is the recommended treatment for horses with clostridial myonecrosis?

A

oxygen therapy!!!!

fenestrate the wound, antimicrobials, anti-inflammatories, & supportive care

92
Q

what is the toxin in box elder trees that causes atypical myopathy?

A

hypoglycin a

93
Q

what is another name for atypical myopathy?

A

seasonal pasture myopathy

94
Q

what season do we commonly see atypical myopathy?

A

fall

95
Q

T/F: atypical myopathy is highly fatal in horses

A

true

96
Q

what are the clinical signs associated with atypical myopathy?

A

stiffness, difficulty walking/standing, myoglobinuria, difficulty breathing, recumbency/collapse, & death

97
Q

what are 5 examples of vitamin e related equine neuromuscular disorders in horses?

A

nutritional myodegeneration, neuroaxonal dystrophy, equine degenerative myeloencephalopathy, vitamin e deficient myopathy, & equine motor neuron disease

98
Q

what horses are affected by white muscle disease? why?

A

foals - deficiency of selenium in utero

99
Q

what is the prognosis of white muscle disease?

A

good without any cardiac involvement

100
Q

how is white muscle disease treated?

A

injectable selenium, supportive care, & vitamin e

101
Q

what clinical signs are associated with white muscle disease in foals?

A

muscle weakness/pain/stiffness, trembling of the limbs, prolonged recumbency/difficulty rising, aspiration pneumonia, & sudden cardiac death

102
Q

what are the clinical signs associated with equine motor neuron disease in horses?

A

weakness, weight loss despite a normal appetite, elephant on a ball stance, low head carriage & elevated tail head, & shifting weight or recumbency

103
Q

how is equine motor neuron disease diagnosed?

A

serum vitamin e & muscle biopsy

104
Q

how is equine motor neuron disease treated?

A

vitamin e

105
Q

how is PSSM type II diagnosed?

a. edta whole blood genetic test
b. muscle biopsy
c. hair roots genetic test
d. wait - there are 2 types of PSSM?

A

b. muscle biopsy

106
Q

what is the mode of inheritance of HYPP?
a. autosomal dominant
b. autosomal recessive
c. K+ channel defect
d. x-linked dominant

A

a. autosomal dominant

107
Q

s. equi infections have been associated with which myopathy?
a. post-injection myonecrosis
b. atypical myopathy
c. summer pasture associated myopathy
d. immune mediated myositis

A

d. immune mediated myositis

108
Q

this horse is showing an ‘elephant on a ball stance’ - this is concerning for what disease?

A

equine motor neuron disease

LA DX & TX II (44 decks)

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