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Neurology > Muscle/Nerve biopsy > Flashcards

Muscle/Nerve biopsy Flashcards

1
Q

What are 4 standard muscles biopsied?

Muscle samples for what type of microscopy should be harvested first?

A
  1. Lateral head of the triceps (distal 1/3)
  2. Vastus lateralis (distal 1/3)
  3. Cranial tibial (proximal 1/3)
  4. Temporalis muscles

Samples for EM should be harvested first - collected before manipulation of the myofibers

  • Immersed in glutaraldehyde fixative

(VCNASAP Dickinson)

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2
Q

How can H&E stain can be used to evaluate muscle biopsy?
What do basophilic fibers mean?
What do pale fibers mean?

A

H/E - general histopathologic features

Basophilic fibers - degenerating/regenerating fibers

Pale fibers - necrotic

(VCNASAP Dickinson)

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3
Q

What features can be studied in muscle biopsies stained with modified trichome?

What 4 pathologies can be identified on modified trichome stain?

A

General histopathologic features

  • membranous structures stain red (nuclei, mitochondria, sarcoplasmic reticulum)
    • intramuscular nerve fibers (myelin) stains red
  • collagen and myofibers stain blue

Pathology:

  1. nemaline rods (extensions of z-line proteins, stain red)
  2. ragged red fibers
  3. loss of myelinated nerve fibers
  4. fibrosis

(VCNASAP Dickinson)

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4
Q

What muscle biopsy stain is used to differentiate between type 1 and 2 myofibers?

A

Myofibrillar adenosine triphosphatase (ATPase) pH 9.8

  • Type 1 stain light, type 2 stain dark
  • used to identify fiber type grouping

(VCNASAP Dickinson)

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5
Q

What muscle biopsy stain can be used to differentiate type 2A, 2B, and 2C myofibers?

A

ATPase preincubation pH 4.3 (reversal)

  • Dog: Type 1 Dark, Type 2A light, type 2C intermediate
  • Cat: Type 1 dark, type 2A + B light, type 2C intermediate
    • Type 2A and B are differentaed with ATPase preincubation pH 4.6
      • 2A - light
      • 2B - intermediate
  • Can be used to differentiate chronic denervation and reinnervation (type 1 fibers are dark) from steroid/endocrine myopathy (type 2 fibers light)

(VCNASAP Dickinson)

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6
Q

What 3 structures stain magenta with Periodic acid-Schiff-hematoxylin (muscle biopsy)?

A

External lamina, glycogen, and myelin are positively stained (magenta)

(VCNASAP Dickinson)

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7
Q

What stain is used to evaluate for glycogen storage disease?

A

Periodic Acid-Schiff-hematoxylin

(VCNASAP Dickinson)

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8
Q

What stain is used to highlight intermyofibrillar lipid inclusions and fat cells in mysial connective tissue of muscle biopsies?

A

Oil Red O

  • stains neutral triglycerides
  • there should be NO intramyofiber lipid stores

(VCNASAP Dickinson)

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9
Q

What stain is used to diagnose lipid storage myopathy?

A

Oil red O

(VCNASAP Dickinson)

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10
Q

What two stains are available for mitochondrial oxidative enzymes (muscle biopsy)?

Which one can also identify tubular aggregates?

A
  1. Nicotinamide adenine dinucleotide-tetrazolium reductase (NAD reductase)
    • Can also identify tubular aggregates (sarcoplasmic reticulum)
  2. Succinate dehydrogenase

(VCNASAP Dickinson)

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11
Q

What stain is used to highlight lysosomes in macrophages in muscle biopsy?

A

Acid phosphatase - lysosomes stain red

  • Stains lysosomal deposits in acid maltase deficiency
  • Used primarily in inflammatory myopathies

(VCNASAP Dickinson)

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12
Q

_______ should not stain normal muscle, but if dermatomyositis is present, there will be positive staining.

A

Alkaline phosphatase

(VCNASAP Dickinson)

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13
Q

____________ should not stain normal muscle, but if there is immunoglobulin deposition, there will be positive staining

A

Staphylococcal protein A-horseradish peroxidase

  • No staining in normal tissues
  • Immunoglobulin deposition in immune-based disease (nuclear, sarcolemmal, diffuse, neuromuscular junction)
  • Stains eosinohils black
  • Artifactually stains necrotic fibers

(VCNASAP Dickinson)

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14
Q

What 2 structures are stained positively with esterase stain (muscle biopsy)?

A
  1. Localization of motor endplate (acetylcholine)
  2. Lysosomes in macrophages

(VCNASAP Dickinson)

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15
Q

What can be causes of lipid storage myopathy? (3)

A
  1. fatty acid oxidation disorder
  2. primary or secondary carnitine deficiency
  3. endocrine myopathy

(VCNASAP Dickinson)

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16
Q

What muscle enzyme stain identifies inclusions in muscle biopsies?

A

Congo red - stains inclusions in muscle biopsies

  • highlights amyloid deposits

(VCNASAP Dickinson)

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17
Q

What muscle biopsy stains are used to detect immunophenotype?

A
  • CD3 - T cell population
  • CD21 - B cell population
  • CD4 - macrophages
  • CD8 - dendritic

(VCNASAP Dickinson)

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18
Q

What type of artifact? (left is normal)

A
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19
Q

What type of stain is this?

A
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20
Q

What type of stain and what pathology is shown?

A
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21
Q

What type of stain?

What is the anatomic structure?

A
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22
Q

What type of stain?

What anatomic structure is shown?

A

Modified Gomori Trichome

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23
Q

What type of pathology is shown?

What breeds? (3)

A

Nemaline rod

  • Mutated Genes:
    • Skeletal
    • α-actin
    • Nebulin
    • Tropomyosin 2
    • Tropomyosin 3
    • Troponin T
    • Cofilin 2
  • Nemaline rod myopathy – Congenital nemaline rod myopathy has been reported in the Border Collie, cats and most recently in American Bulldogs
    • A mutation has been identified in the Nebulin gene in American Bulldogs

(Shelton)

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24
Q

What is the stain?

What pathology is shown?

A

Ragged red fiber = accumulations of abnormal mitochondria

Modified Trichome

(Shelton)

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25
Q

What sort of staining/reaction is shown?

A
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26
Q

What sort of pathology is shown?

A
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27
Q

What sort of pathology is shown?

A
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28
Q

What sort of pathology is shown?

A
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29
Q

What type of staining is this? What is it used to detect?

A
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30
Q

What type of stain is this? What is it used to detect?

A
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31
Q

What type of stain is this? What is it used to detect?

A
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32
Q

What is the utility of these 2 staining techniques?

A
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33
Q

What pathology is depicted?

A
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34
Q

What kind of stain/reaction is shown?

A
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35
Q

What kind of stain/reaction is depicted and what is it used to identify?

A
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36
Q

What kind of stain?

A
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37
Q

Polymyositis: Diagnostic criteria (5)

A
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38
Q

Necrotizing myopathy (rhabdomyolysis) causes (9)

A
  1. metabolic defects (fatty acid oxidation, mitochondrial, glycolytic)
  2. Primary myopathy (muscular dystrophy)
  3. drug sensitivity
  4. loss of membrane integrity
  5. snake toxins, spider toxin, venomous insect sting
  6. salt and water imbalance
  7. electrolyte abnormalities
  8. infectious
  9. idiopathic

Shelton PPT

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39
Q

What are the 4 categories of muscular dystrophy?

A
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40
Q

What is the pathology and what is the mutation

A

Labrador w. centronuclear myopathy - internal nuclei are seen later in life

Great dane - mutation in BIN1 gene

Border collie - mutation in DNM2 gene

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41
Q

What is the disease?

A
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42
Q

What muscle fibers satisfy the following characteristics:

  1. aerobic and oxidative metabolism
  2. slow speed of contraction
  3. do not fatigue
  4. postural muscles

What are their staining characteristics?

A

Type I myofibers

  • Stain strongly with mitochondrial stains (reduced NAD reductase, succinate dehydrogenase)
  • stain strongly for oxidative substrates (lipid, oil red O)

(VCNASAP Dickinson)

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43
Q

What myofiber type has the following characteristics?

  • anaerobic glycolytic metabolism
  • fast speed of contraction
  • phasic/movement muscles

What is the staining characteristic?

A

Type 2 myofibers

  • stain strongly for substrates such as glycogen (PAS)

(VCNASAP Dickinson)

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44
Q

What are the 4 subtypes of type 2 myofibers

A

2A: also have oxidative metabolic capacity

2B: utilize only anaerobic glycolysis and fatigue rapidly

2C: rare in mature animals of all species, found predominantly in the neonate < 12 weeks

2M: Found in the dorsal muscles of the first brachial arch origin (masticatory muscles)

  • stable myofibrillar ATPase rxn at pH 4.3
  • do NOT show the typical reversal of staining seen with type 2A and 2B myofibers
  • masticatory muscles also have some type 1 muscle fibers

(VCNASAP Dickinson)

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45
Q

If a denervated fiber is not reinnervated, atrophy and loss of myofibrils progress until only myonuclei remain enclosed within the sarcolemma. This is called ________________

A

pyknotic nuclear clumps

  • represent the end stage of chronic denervation, and may require some months to develop

(VCNASAP Dickinson)

46
Q

______ is the term for when two or more myofibers seem to be occupying the space expected for a single myofiber

A

Fiber type splitting

  • frequent nonspecific finding in primary myopathic disease
  • may be a normal feature near the myotendinous junction

(VCNASAP Dickinson)

47
Q

What muscle pathologies have frequent internal nuclei on muscle biopsy?

A

Myotonia

Muscular dystrophy

Internal nuclei

  • Central migration of the myofiber nuclei - nonspecific response
  • may be occasionally seen in skeletal muscle biopsy specimens from clinically normal dogs/cats
  • should not exceed 1-2% of total myofibers

(VCNASAP Dickinson)

48
Q

Accumulations of ultrastructurally normal mitochondria in muscle biopsies appear as _____ on trichome stained sections

A

“ragged red” fibers on trichome

(VCNASAP Dickinson)

49
Q

What kind of test is the 2M antibody titer?

What breed gets a particularly severe form of MMM as a young dog?

A

2M titer = ELISA test

Young cavaliers

(VCNASAP Dickinson)

50
Q

What are the diagnostic criteria for immune-mediated polymyositis?

A
  1. Inflammatory biopsies in multiple muscles
  2. elimination of identifiable cause
  3. cellular infiltration into nonnecrotic fibers
  4. cellular infiltrates contain CD8+ T cells (upregulation of MHC 1 immune response)
  5. upregulation of MHC antigens

Shelton PPt

51
Q

Recently, a metabolic cause of presumed immune-mediated generalized myositis was identified in a family of _________ dogs with a mutation in the mitochondrial _______

A

Recently a metabolic cause of presumed immune-mediated generalized myositis was identified in a family of Dutch Shepherd dogs with a mutation in the mitochondrial aspartate/glutamate carrier, leading to a highly oxidizing intramitochondrial environment and an inflammatory myopathy

Shelton

52
Q

~ 8 infectious causes for myositis?

A
  1. Toxoplasma/neospora/sarcocystis
  2. Hepatozoonosis
  3. Trypanosomiasis
  4. Microfilariasis
  5. Leishmaniasis
  6. Tick borne disease
  7. Viral (FeLV, FIV)
  8. Bacterial (Lepto, clostridial)

Shelton

53
Q

4 neoplasias that cause paraneoplstic myositis?

A
  1. Thymoma
  2. lymphoma
  3. mast cell tumor
  4. carcinoma

Shelton

54
Q

What two stains are mitochondrial specific?

A
  1. Cytochrome C oxidase
  2. Succinic dehydrogenase

(Shelton)

55
Q

Maximum normal myofiber diameter is present by ______ of age in dogs

How does breed influence myofiber size?

A

6 mos

Larger breed –> larger myofiber diameter

(Dickinson)

56
Q

Drugs associated with secondary myositis?

A
  1. D-penicillamine
  2. Cimetidine
  3. Trimethoprim-sulfa
  4. Tapazole

(Shelton)

57
Q

What is the most common type of muscular dystrophy in dogs?

A

X-linked dystrophin deficient muscular dystrophy

(Shelton)

58
Q

Where is laminin alpha 2 found in the muscle?

Where is sarcoglycan found in the muscle?

A

Laminin alpha 2 - extracellular ligand for dystrophin-associated glycoprotein complex, that links dystrophin to the extracellular matrix and contributes to the stability of the basement membrane

  • Deficiency of laminin alpha 2 has been reported in cats and dogs, specific mutations not identified

Sarcoglycan - part of the dystrophin-glycoprotein complex

  • Stabilizes myofiber membranes during contraction
  • Sarcoglycan deficiency seen in Boston terrier

(Shelton)

59
Q

What are the broad categories of myopathy (6)

A
  1. Inflammatory
  2. Muscular dystrophy
  3. Myasthenic syndromes
  4. Congenital structural myopathy
  5. Channelopathies
  6. Metabolic myopathies

(Shelton)

60
Q

What breeds centronuclear x-linked myotubular myopathy?

A

Lab

Rottweiler

Boykin Spaniel

Mutations in the myotubularin gene

(Shelton)

61
Q

What staining technique is used for diagnosing congenital myasthenic syndromes?

A

Cryosections of muscle used to localize motor end plates with serial sections stained with labeled alpha-bungarotoxin (for localization of the AChRs)

  • Mutations of the COLQ gene encoding the collagenous tail of acetylcholinesterase have been reported in the labrador

(Shelton)

62
Q

What can cause type I myofiber atrophy? (2)

A

Immobilization/tenotomy - shortening of a muscle’s resting length secondary to trauma/tenotomy

Nemaline rod myopathy - type I fibers often affected

(Dickinson)

63
Q

What causes selective type II myofiber atrophy? (6)

A
  1. Disuse/cachexia
    • Atrophy of all myofiber types may occur with type II myofibers usually proportionally more affected
  2. Excess glucocorticoids
  3. Neoplasia - carcinomas, adenomas, lymphosarcoma
  4. Hypothyroidism (hyperthyroidism may result in type II fiber predominance)
  5. Myasthenia gravis (reported in humans)
  6. Other - nemaline rod myopathy, leptomeningitis, polyneuropathy, polyradiculoneuritis, encephalomyelitis

(Dickinson)

64
Q

How does one determine if there is a myofiber paucity or predominance?

What causes paucity?

A

Requires quantitative analysis of numbers of myofiber types, and knowledge of normal myofiber proportions in a specific muscle

Paucity: selective atrophy, loss of myofibers, failure of development

(Shelton)

65
Q

What can be used to support diagnosis of acquired MG on muscle biopsy?

A

Demonstration of IG at the neuromuscular end plate using consecutive sections of muscle stained with esterase to localize end plates

Peroxidase conjugates of staphylococcal protein (binds canine IgG)

Can incubate P serum with muscle biopsy prior

Demonstration of circulating autoantibodies to AChR by immunoprecipitation radioimmunoassay has superseded antibody localization on muscle biopsy specimens

(Shelton)

66
Q

What criteria should be used to decide what nerve to biopsy?

What nerve is a good choice if there is generalized neuromuscular disease?

A
  1. Should be affected by the disease process based on:
    • Abnormal electrophysiologic investigation
    • Neurologic abnormalities in areas innervated by the nerve
  2. Easily biopsied with low morbidity
  3. Has established normal electrophysiologic and morphometric data
  4. Innervates a muscle that is routinely biopsied, and for which normal histochemical and morphometric data is available

Common peroneal is a good choice - easy to identify, well established references, mixed nerve with sensory, motor and autonomic fibers

  • Ulnar and tibial nerves also easy to biopsy

(Dickinson)

67
Q

If a predominantly sensory neuropathy is suspected, what nerves should be biopsied?

A

Caudal cutaneous antebrachial nerve in the thoracic limb

Caudal cutaneous sural nerve in the pelvic limb

Biopsy of the dorsal nerve root is preferred, normally results in minimal neurologic deficits after surgery

(Dickinson)

68
Q

What are the 3 ways that nerves are prepared/processed for examination?

A
  1. Routine histologic staining of formalin-fixed specimens
    • Basic assessment and screening for loss of myelin, axonal degeneration, other gross abnormalities, cellular infiltration
  2. Plastic embedding of glutaraldehyde fixed specimens
    • Semithin cross-sections of nerve stained with toluidene blue for light microscopy, and ultrathin sections for EM
    • More detailed investigation of peripheral nerve pathologic findings
    • Morphometric data of myelin sheaths may be obtained and results may be compared with normal values
  3. Single teased fiber preparations
    • Small strands of glutaraldehyde fixed nerves are treated with glycerol and osmium tetroxide –> teased apart under magnification until single fibers are present –> study myelinated fibers
    • Assessment of consecutive myelin internodes in the same nerve fiber
    • Used to determine the frequency of certain neuropathologic abnormalities such as areas of demyalination or remyelination, and the presence of ongoing nerve fiber degenration

EM rarely required in the clinical setting

(Dickinson)

69
Q

What are the three broad types of changes identified in nerve biopsy?

A
  1. Axonal degeneration
  2. Axonal dystrophy
  3. Primary demyelination

(Dickinson)

70
Q

What causes axonal degeneration?

A
  • Trauma, toxins, metabolic abnormalities, loss of motor neurons, or axonopathy of undetermined cause –> axonal degeneration
  • Axonal loss –> secondary loss of myelin sheath with formation of lg myelin ovoids and myelin balls
  • Easily seen in teased fibers and cross-sectional preparations

Biopsy will give information RE severity, chronicity, and presence of regeneration

(Dickinson)

71
Q

What is axonal dystrophy?

A

Multifocal accumulations of cytoskeletal elements (microtubules, neurofilaments) –> axonal swellings or spheroids

(Dickinson)

72
Q

What causes primary demyelination and what does it look like?

A
  • Diseases affecting the myelin sheath or the Schwann cells producing it –> loss of myelin
  • Best seen in teased fiber preparations
    • Myelin loss is segmental, may involve entire internode or only the paranodal region
  • Myelin ovoids smaller than those seen when the entire axon degenerates
  • Normal appearing axons that are being remyelinated may have inappropriately thin myelin sheaths
  • Chronic - proliferation of Schwann cells around the demyelinated axon –> onion bulb

(Dickinson)

73
Q

What are the pathologies/which is normal

A
74
Q

When is morphometric analysis of nerve fibers helpful?

A

When myelinated fiber density is normal

(picture) Shows drop out of larger myelinated fibers

(Shelton)

75
Q

How can unmyelinated C fibers be evaluated?

A

Skin biopsy

These fibers are not evaluated on regular nerve biopsy or nerve conduction study

(Shelton)

76
Q

What can frozen nerve sections evaluate?

A

Estimate of fiber loss and myelin ovoids

Immunohistochemistry and immunophenotypic identification of cellular infiltrates

Cannot evaluate demyelination, regeneration, or perform morphometric analysis

(Shelton)

77
Q
A
78
Q

What nerve pathology is shown?

A

Axonal degeneration

Axons swell initially, have basophilic appearance (right)

Then degeneration of organelles within the axon (left)

(Shelton)

79
Q

What is the pathology?

A

Axonal degeneration - myelin ovoids

  • First change seen with axonal degeneration, is present on light microscopy about 36 hours after injury
  • Myelin sheath breaks to form ellipsoids around axonal debris - 4 days
  • Myelin ellipsoids break into smaller ovoids and balls of degenerating myelin lipids
  • Removed by macrophages

Yellow arrows - myelin ovoids

White - degenerating axon

(Shelton)

80
Q

What nerve pathology is shown

A

Foamy macrophages that are cleaning up axonal degeneration

(Shelton)

81
Q

What nerve pathology is shown

A

Chronic axonal loss

Endoneurial fibrosis

End stage axonal degeneration

The next question is - are there any regenerating clusters

(Shelton)

82
Q

What nerve pathology is shown

A

Regenerating clusters

  • Closely packed axonal sprouts track along original basal laminal tube
  • Marker for axonal regeneration
  • If they do not make contact with suitable end organ, will degenerate
  • Failure of neurotrophic lure to periphery may result in undirected tangle (neuroma)

(Shelton)

83
Q

What nerve pathology is circled

A

Axonal degeneration with regenerating cluster

It is important to note a single basal lamina to confirm that it is regenerating

(Shelton)

(Shelton)

84
Q

Nerve pathology

A

Regenerating sprouts

This dog has a good chance for recovery

(Shelton)

85
Q

What is the nerve pathology?

A

Renaut bodies

The significance is uknown

They are seen in mice on wire cage floors and old dog

Increased endoneurial pressure?

(Shelton)

86
Q

What is the nerve pathology

A

Bunger bands

  • Associated with axonal degeneration
  • Columns of Schwann cell processes extending away from the undamaged part of the myelinated fiber
  • Act as guides for regenerating sprouts

(Shelton)

87
Q

What breed has a sensory neuropathy caused by FAM134B?

A

Border Collie

(Shelton)

88
Q

Causes of acquired axonopathy

A
  1. Diabetes
  2. Hypothyroidism
  3. Trauma
  4. Ischemia
  5. Toxic - lead, organophosphate, vincristine, cisplatin, acrylamide, metronidazole, nitrofurantoin
  6. Nutritional (B1, B6, B12)
  7. Immune-mediated - chronic relapsing polyneuropathy
  8. Neoplastic/paraneoplastic
  9. Chronic uremia

(Shelton)

89
Q

nerve Pathologic changes associated with feline diabetes mellitus?m

A

Demyelination

Axonal degeneration with ability to regenerate

(Shelton)

90
Q

Feline nerve pathology

A

Diabetic neuropathy with ballooning

no evidence of axonal degeneration here

(Shelton)

91
Q
A

A - Normal

B - paranodal demyelination

C - segmental demyelination

D - whole internode demyelination

E - axonal degeneration

Spectrum of changes associated with diabetic neuropathy
Myelinated nerve fiber density is higher in nondiabetic than diabetic patients

(Shelton)

92
Q

Causes of hypo/hyper/dysmyelination

A

Schwann cell abnormalities - Metabolic interference with normal metabolism of Schwann cell. Results in primary segmental demyelination, conduction block

Myelin abnormalities - Autoimmune demyelination with lymphocytic and macrophagic infiltration into nerve

Secondary demyelination - Failure of myelin sheath to adapt to changes in the axon diameter

Hypomyelination - Myelin sheath never attains normal thickness relative to the axon size

Hypermyelination - Tomacula formation

(Shelton)

93
Q

Nerve pathology?

A

3m DLH with progressive weakness

Numerous inappropriately thin myelinated fibers for the axon diameter

Hypomyelinating polyneuropathy

(Shelton)

94
Q

Recurrent demyelination and remyelination polyneuropathy is seen in what breed of cat?

A

Bengal

  • Muscle biopsy - thinly myelinated fibers and onion bulb formation of intramuscular nerve fibers
  • 1-3 years of age
  • Prognosis is good
95
Q

What is the pathology? (right is normal)

A

Bengal demyelinating/remyelinating polyneuropathy

Myelin staining is pink

(Shelton)

96
Q

What is the pathology?

A

Bengal demyelinating/remyelinating polyneuropathy

Variable severity in changes between nerve fasicles (seen on left)

Right - 400x higher power shoring edema and early onion-bulb formations (toluidene blue)

(Shelton)

97
Q

What is the pathology?

A

Remyelination: onion-bulb formation

  • Removal of myelin debris by macrophages
  • Normal Schwann cells divide and spread inside basal lamina tube to cover the bare internode
  • Replacement of one original internode by several shorter segments of varying length and thickness
  • Onion bulb formations - hypertrophic change from repeated episodes of demyelination and remyelination

(Shelton)

98
Q

Polyneuropathy seen in Miniature Schnauzer at 1-2 months?

A

Demyelinating neuropathy - focally folded myelin sheaths

  • Initial clinical signs at 1-2 mos
  • Clinical signs variable but may include megaesophagus, laryngeal paralysis, and generalized weakness
  • Generalized EMG changes including fibrillation potentials
  • MNCV - dramatically reduced
  • CMAP amplitudes mildly reduced
  • Mutation in MTRM13/SBF2
  • Teased nerve fiber - variably myelin thickness in biopsy from ulnar nerve, segmental demyelination, areas of thickened myelin consistent with tomacula

(Shelton)

99
Q

What is the pathology?

A

A, B - segmental demyelination

C-E - areas of thickened myelin consistent with tomacula

Samples from miniature schnauzers

(Shelton)

100
Q

Muscle biopsy

A

Necrotizing myopathy

here is extensive muscle necrosis without lymphocytic infiltration.Cellular infiltrates are restricted to macrophages and are appropriate in number to the degree ofmuscle necrosis

Shelton

101
Q

What are the criteria for clinical syndrome of rhabdomyolysis? (5)

A
  1. Acute muscle necrosis
  2. Swollen painful muscles (myalgia)
  3. Limb weakness/collapse
  4. Markedly elev. serum CK
  5. Myoglobinuria

(Shelton)

102
Q

What is the common pathophysiologic mechanism of rhabdomyolysis?

A

Direct injury to the sarcolemma or failure of energy supply in the muscle –>

common final pathophysiologic mechanism is uncontrolled rise in free intracellular calcium concentration + activation of Ca-dependent proteases

Result in destruction of myofibrils + lysosomal digestion of muscle fiber contents

(Shelton)

103
Q

How does myoglobin differ from hemoglobin?

A

Myoglobin - major protein in muscle sarcoplasm functioning as oxygen store (seen in oxidative fibers)

Hb binds 4 molecules, Mb binds 1 molecule of oxygen

Hb (and other muscle proteins) are insoluble @ pH 8

Myoglobin remains soluble

(Shelton)

104
Q

2 ddx for recurrent myoglobinuria

A
  1. Disorders of FA oxidation and mitochondrial myopathy
  2. Muscular dystrophy

(glycogen storage diseases reported to cause myoglobinuria in humans, this has been identified in cattle and horses but not in dogs/cats)

(Shelton)

105
Q

Drugs/toxins that can cause myoglobinuria

A
  1. Metabolic effects
    • Alcohol
    • CO
    • Cholesterol lowering drugs
    • Azathioprine
  2. Direct effect on muscle membranes
    • Snake envenomation
    • Hornet, spider, wasp, bee sting/bite
    • Monensin – inophone antibiotic used to treat cattle
  3. Hypokalemia
    • Diuretic use
    • Theophylline
    • Amphotericin B
  4. Exercise and fever
    • Neuroleptics (antipsychotics)
    • Strychnine
    • Amphetamine/methamphetamine
    • Theophylline
    • Tetanus toxin
  5. Ischemia - cocaine…

(Shelton)

106
Q

Infectious agents that can cause myoglobinuria/myonecrosis?

A

Babesiosis, Neosporosis

(Shelton)

107
Q

Electrophysiology (EMG, NMV, M wave) and muscle biopsy findings in dog w/ motor neuron disease?

A

EMG - denervated muscle

NCV - depends on stage of disease
Classic findings - normal NCV + decreased M wave amplitude - reflects loss of axons (some neurons are still surviving and axons conduct normally)
Progressive disease - decreased NCV due to loss of largest/fastest axons

Muscle biopsy - denervation –> variation in myofiber size, marked angular atrophy of denervated fibers

Nerve biopsy - normal or reduced numbers of axons + axonal degeneration

(VCNASAP Olby)

108
Q

What disease in great danes causes progressive muscle wasting, exercise intolerance, general body tremors and collapse?

A

Central core-like myopathy in great danes

HE muscle biopsy - well defined central basophilic areas within many myofibers that react with oxidative reactions

(VCNASAP Platt)

109
Q

Springer spaniel with PAS+ stained vacuoles in muscle likely has?

A

Muscle-type phosphructokinase deficiency

In dogs - clinical signs typically related to hemolysis but there will be vacuoles in up to 10% of myofibers of affected animals

(VCNASAP Platt)

110
Q

Nerve and muscle biopsy findings with feline diabetic neuropathy

A

Nerve:
Schwann cell injury –> myelin splitting/ballooning –> demyelination and scattered axonal degeneration

Neurology (12 decks)

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