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Y4 Equine - Lameness & Orthopaedics > Pathophysiology of muscle disease > Flashcards

Pathophysiology of muscle disease Flashcards

1
Q

Types of muscle dz

A
  • Exertional
  • Non-exterional
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2
Q

Exertional muscle dz

A

Acquired:
- ‘tying-up’

Genetic:
- PSSM-1
- PSSM-2
- RER
- HYPP
- Myofibrillar myopathy

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3
Q

Non-exertional muscle dz

A

Acquired:
- Toxic: AM
- IMM
- Traumatic: atrophy
- Infectious: Clostridium spp

Genetic:
- MH
- Mitochondrial myopathies
- IMM

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4
Q

Other names for sporadic rhabdomyolysis

A
  • tying-up
  • monday-morning disease
  • rhabdomyolysis
  • azoturia
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5
Q

What is the most common muscular disorder in horses?

A
  • Sporadic rhabdomyolysis
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6
Q

Sporadic rhabdomyolysis - CS

A
  • stiff
  • stilted gait
  • excessive sweating
  • increase respiratory rate after exercise
  • firm painful muscles (hindquarters, back)
  • reluctant to move
    forward
  • occasional dark urine
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7
Q

Causes of sporadic rhabdomyolysis

A
  • overexertion
  • dietary imbalances
  • exhaustion
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8
Q

Overexertion causing sporadic rhabdomyolysis

A
  • increase in work intensity without a strong musculoskeletal foundation Z- disk instability
  • overstretching of myofibers
  • sarcolemma stretching
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9
Q

Dietary imbalance causing sporadic rhabdomyolysis

A
  • Electrolytes (Na and Ca) both important in neural transmission and muscle contraction
  • Low Vitamin E intake: poor antioxidant state
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10
Q

Exhaustion causing sporadic rhabdomyolysis

A

TB and endurance horses training in hot, humid weather: electrolytes loss in sweat and dehydration

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11
Q

What is RER

A

= recurrent exertion rhabdomyolysis
- intermittent form of rhabdomyolysis in horses likely linked to abnormal calcium regulation in myofibres
– SERCA receptor dysfunction?

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12
Q

Prevalence of RER

A
  • 5% TB
  • 6.5% SB
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13
Q

RER risk factors

A

➢ Fit horse with nervous temperament»epinephrin/adrenaline release?
➢ Young mares more at risk, but no associated with oestrus cycle
➢ Lack of turnout
➢ Held back during gallop: epinephrin and cortisol release?

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14
Q

What does the SERCA receptor do?

A
  • allows removal Ca from sarcoplasm leading to relaxation
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15
Q

What does the RYR-1 receptor do?

A
  • allows release of Ca to stimulate contraction
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16
Q

How does adrenaline affect the RYR-1 receptor?

A
  • it increases it’s activity
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17
Q

What is PSSM-1?

A

= polysaccharide storage myopathy 1

➢Abnormal storage of glycogen in muscle fibres difficult to be metabolized by muscle cells
➢Genetic mutation in GY1: Glycogen synthase enzyme turn on constantly: PSSM-1
➢A subset of cases: amylase sensitive glycogen»>PSSM-2»>Myofibrillar myopathy & PSSM-2

18
Q

Prevalence of PSSM-1

A

➢Highest in continental European draft breeds
➢Percheron Belgians
➢Shires and Claydesdales low in UK: Irish draft, Connemaras, Cobs present
➢Quarter horses (28%), Appaloosas (10%)
➢Very rare in light breeds: SB, TB, Arabians

19
Q

PSSM-1 risk factors

A

➢breed and exercise of more than 20min in one session
➢Owner perception : high quality grass available

20
Q

What do both PSSM-1&-2 cause?

A
  • a myofibrillar myopathy (oxidative deficit)
21
Q

PSSM-1 breeds & clinical presentation

A

➢Most draft horses are asymptomatic
– unless performance drafts
➢Stiffness after a short period of exercise
–reluctance to move forward, poor performance, sweating or more severe clinical signs: myoglobinuria
➢Mean age at diagnosis 4-8 years-old

22
Q

What is PSSM-2?

A

➢Big box of muscle conditions with some accumulation of glycogen
– likely different aetiologies and/or mutations

23
Q

Prevalence of PSSM-2

A

➢ 28% QH or American breeds
➢ Other light breeds such as Friesians, Selle francais, Morgans, Appaloosas, Arabs, occasional TB

24
Q

PSSM-2 CS

A
  • more subtle with poor performance mainly, milder elevation of muscle enzymes post exercise
25
Myofibrillar myopathy
➢ No always associated with severe increase in muscle enzymes (Arabs>>>>WB) ➢ Abnormal Desmin protein unable to support Z-disk: contractile apparatus dysfunction> fibrillar rupture ➢ Cysteine metabolism deficiency: core pathway for cytoplasmatic anti-oxidants
26
Myofibrillar myopathy presentation / presenting signs
➢ Poor performance ➢ Lack of hindlimb engagement
27
What is HYPP?
= hyperkalaemic periodic paralysis ➢ Na channels are ‘leaky’ : prolonged depolarization and abnormal action potentials ➢ High K might precipitate episodes: high sensitivity to small variations in K
28
Prevalence of HYPP
➢Quarter Horse and QH derived breeds: QH Impressive stallion lines>>SCN-4A gene
29
HYPP CS
➢ Sporadic attacks of stiffness, muscle tremors, weakness and collapse ➢ Breathing difficulties: Paralysis of laryngeal muscles>>stridor ➢ Prolapse of third eyelid
30
What is equine atypical myopathy?
❖Toxic rhabdomyolysis associated with Hypoglycin A ingestion (from sycamore) ❖Myofibrillar metabolic impairment of aerobic metabolism -- Postural muscles -- Intercostal muscles -- Myocardium
31
Outbreak presentation of equine atypical myopathy
- Autumn & Spring: toxic plant material on pastures
32
Mortality rate of equine atypical myopathy
- 68%
33
What do we know about Hypoglycin A?
➢Naturally occurring amino acid found in some trees of Sapindaceae family (including Acer) with unknown function in plants -- Deterrent to avoid herbivore consumption? -- Or Growth factor important for plant development? ➢Not believed to be toxic per se: clearance as free molecule by liver, however, becomes toxic once metabolised in the mitochondria: -- toxicity might be dose related?
34
Equine atypical myopathy CS
▪ Stiffness, muscle fasciculations, weakness, sweating and myoglobinuria (~90%) ▪ Colic, tachycardia, tachypnea, recumbency, distended bladder, reduced/Absent GI sounds ▪ Dysphagia (25%) ▪ Cardiorespiratory arrest -> euthanasia
35
Immune mediated myopathy causes
- Normally associated with previous respiratory infection (Strep. infections, viral (Flu and EHV), Corynebacterium) - Purpura haemorrhagica - Streptococcal myopathy - QH immuno-mediated myopathy
36
Purpura haemorrhagica
- 10 days after S. equi infection>> severe vasculitis with muscle infarction
37
Streptococcal myopathy
- occurs at the same time that classical strangles sings: stiffness and recumbency
38
QH immuno-mediated myopathy
- Precipitated by respiratory infection (Strepp +++) - Lines predisposed genetically: MYI mutation makes myosin chaines (2Xa) similar to Strep prot M >> recgonised by immune system: molecular mimicry - Lethargy, rapid muscle atrophy epaxial and rump muscles
39
Myonecrosis
➢ Most common due to Clostridium spp, but other anaerobic bacteria might be involved -- Clostridum perfringes -- Clostridium septicum ➢ IM injections or puncture wounds NSAIDs and Vitamins most common ➢ Occur 6-72 hours post injection: cervical musculature, gluteal and thigh muscles
40
Myonecrosis CS
- fever - stiffness - severe pain - gangrene - crepitation

Y4 Equine - Lameness & Orthopaedics (34 decks)

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