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Pathology > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

Changes in bloodwork with muscle damage

A

Elevations in:
Creatinine kinase (CK)
Lactate dehydrogenase (LDH)
Aspartate aminotransferase (AST)
Alanine aminotransferase (ALT)

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2
Q

Changes in urine with muscle damage

A

Myoglobinuria (myoglobin released into bloodstream + filtered by kidney into urine)

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3
Q

Muscle atrophy

A

Loss of myofilaments (actin + myosin) —> decrease in myofiber size

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4
Q

Causes of muscle atrophy

A

Denervation
Disuse
Malnutrition

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5
Q

Histology of denervation atrophy

A

Patchwork myofiber atrophy (due to motor unit organization)

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6
Q

Causes of denervation atrophy

A

Wallerian degeneration (most common) - secondary to trauma to peripheral nerve

(Rarely) Axonal degeneration or demyelination

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7
Q

Example of denervation muscle atrophy

A

Laryngeal hemiplegia

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8
Q

Reinnervation

A

Schwann cells proliferate at motor end plate of denervated fiber

Reinnervatioin by collateral sprouting or axon regrowth —> hypertrophy (regeneration of muscle)

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9
Q

Histology of disuse muscle atrophy

A

Diffuse myofiber atrophy

Cells uniformly decreased in size (due to low mechanical load)

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10
Q

Causes of hypertrophy

A

Exercise conditioning

Compensatory hypertrophy (compensation for loss of other myofibers)

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11
Q

Histology of hypertrophy

A

Diffuse enlargement of muscle cells

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12
Q

Histology of muscle degeneration

A

Multifocal (or regional) random pattern
Hydropic swelling, fatty change

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13
Q

Causes of muscle degeneration

A

Peracute/acute nutritional/toxic causes (i.e. selenium deficiency)

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14
Q

Histology of muscle necrosis (myonecrosis, rhabdomyolysis)

A

Segmental (portion of myfiber)
Loss of striations + hyper eosinophilic cytoplasm
Within 24-48 h —> macrophages/neutrophils infiltrate

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15
Q

Sequelae of necrosis

A

Regeneration (if basal lamina intact)

Fibrosis (if basal lamina destroyed)

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16
Q

Process of muscle regeneration

A

Removal of debris by macrophages —> sealing off injured areas —> satellite cell proliferation in basal lamina —> fusion of satellite cells into myofiber

17
Q

Histo/gross appearance of muscle mineralization

A

Chalky white areas of gross specimen

Blue-purple granular material on histo

18
Q

Types of mineralization

A

Dystrophic (necrosis, primary myopathy)

Metastatic (hypercalcemia)

19
Q

Myositis

A

Inflammation of muscle

Follows necrosis

Associated with trauma, infection, infarction, immune-mediated

Inflammatory infiltrate gives clues to cause

20
Q

X-linked muscular dystrophy

A

Mutation of dystrophin gene in young male dogs/cats

Dystrophin helps anchor muscle cell membranes to ECM —> integrity of muscle cell membrane affected

Polyphasic muscle necrosis —> macrophage infiltration / mineralization —> fibrosis

**Golden retrievers, Rottweilers

21
Q

Clinical presentation of muscular dystrophy

A

Diffuse muscle atrophy
Splaying of limbs
Weakness

22
Q

Equine Exertional Rhabdomyolysis

A

Aka: chronic intermittent rhabdomyolysis, exertional myopathy, Monday morning disease, tying up

Acute myofiber necrosis triggered by exercise

Potential cause: metabolic abnormality leading to oxidative damage

Monophonic or polyphasic

23
Q

Clinical pathology of exertional rhabdomyolysis

A

Elevation of CK / AST
Myoglobinuria
(May lead to acute renal failure)

24
Q

Clinical signs of exertional rhabdomyolysis

A

Sudden onset of stiff gait/reluctance to move/pain

+/- swelling of affected muscles (gluteal, femoral, lumbar groups)

25
Q

Equine polysaccharide storage myopathy

A

Carbohydrate metabolism defect

Abnormal aggregates of polysaccharide, variable degress of myofiber necrosis

Related to equine exertional rhabdomyolysis

26
Q

Masticatory myositis

A

Loss of any of muscles of mastication (Masseter, temporal, Pterygoids)

Multifocal, polyphasic necrosis with inflammation (eosinophilic, + lymphocytic)

AUTO-IMMUNE —> autoantibodies to Type 2M myosin isotope and myositigen (myosin-binding protein)

Young large breed dogs predisposed (G. Shepard, Rott)

27
Q

Polymyositis

A

AUTO-IMMUNE - but don’t know protein target of antibodies

Multifocal, polyphasic necrosis with inflammation

Lymphocytic inflammation

Variable clinical signs by muscle affected (weakness, stiff gate, muscle atrophy, regurgitation, etc)

Adult dogs - Boxers, Newfies

28
Q

Extraocular muscle myositis

A

Myositis of extraocular rectus and oblique muscles

RARE, not painful

Multifocal polyphasic necrosis with lymphocytic inflammation

Young female dogs (Goldens)

Immune mediated

29
Q

Immune mediated myositis of horses

A

Associated with Strep equi —> immune complexes of antibodies to strep M protein

Hemorrhagic necrosis of muscle due to vascular injury

Increase in CK/AST, muscle weakness, pain

Vasculitis + fibrinoid necrosis of vascular walls, hemorrhage/infarcts in muscle; inflamm infiltration not seen in muscle

30
Q

Infectious causes of muscle disease

A

Clostridium myositis —> black leg, pseudo-black leg

Leishmania

31
Q

Nutritional myopathies

A

Selenium / Vit E deficiency

32
Q

Toxic myopathies

A

Ionophores
Plants

33
Q

Vascular myopathies

A

Vascular occlusive syndrome
Postanesthetic myopathy in horses
Downer syndrome (LA)
Compartment syndrome

34
Q

Neoplasias

A

Rhabdomyoma/rhabdomyosarcoma
Infiltrative lipoma

Metastatic neoplasms (lymphosarcoma, hemangiosarcoma, malignant melanoma, carcinomas, sarcomas)

35
Q

Rhabdomyoma

A

Benign tumor

Most common in larynx of young dogs —> respiratory distress (difficult to remove, need wide margins)

36
Q

Rhabdomyosarcoma

A

Malignant, locally invasive; Rare

Histologic subtypes:
Embryonal, botryoid, alveolar (young dogs)
Pleomorphic (adult dogs)

37
Q

Common sites of rhabdomyosarcoma

A

Urinary bladder, face skill, tongue

38
Q

Infiltrative lipoma

A

Benign (doesn’t metastasize), but infiltrates muscle

Wide excision is curative but difficult

Pathology (21 decks)

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