MSK Muscle disorders Flashcards

1
Q

Types of muscle disorder:

A
  1. Intrinsic diseases of muscle (myopathies)
    a. Genetically determined
    b. Acquired
  2. Neurological diseases
  3. Fatigue or effort syndrome
  4. Tumours (rare)
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2
Q

Muscular Dystrophies: Characterised by

A

Progressive muscle weakness, defects in muscle prteins, fibre atrophy, and necrosis of muscle cells

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3
Q

Muscular Dystrophies: Types

A

9

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4
Q

Muscular Dystrophies: Most common and severe

A

Duchenne muscular dystrophy (DMD), which involves mutations of dystrophin gene.

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5
Q

Muscular Dystrophies: Becker

A

Less severe form of DMD

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6
Q

Muscular Dystrophies: Dystrophin

A
  • Forms part of transmembrane “dystrophin – glycoprotein complex” that represents the costamere
  • Prevents excessive stress on cell membrane during muscle contraction
  • Stabilises sarcolemma and protects muscle fibre from disruption during contraction
  • Possible role in regulating calcium levels
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7
Q

Muscular Dystrophies: Lack of Dystrophin in studies showed

A

• Increases susceptibility to membrane damage and allows excess calcium to penetrate cell membrane

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8
Q

Metabolic Myopathies: Includes disorders of

A

Glycogen metabolism, lipid metabolism or phosphagen system

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9
Q

Metabolic Myopathies: Cause

A

Impaired energy supply via affected pathways

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10
Q

Mitochondrial Myopathies: Involves

A

Structural abnormalities of mitochondria

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11
Q

Mitochondrial Myopathies: Cause

A

Dysfunction of mitochondrial pathways → impaired aerobic metabolism

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12
Q

Mitochondrial Myopathies: Often linked to

A

Mutations in mtDNA; mutations of nuclear DNA may cause dysfunction in respiratory chain

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13
Q

Disorders of muscle membranes (channelopathies) Periodic paralysis due to

A

Inexcitability of muscle that causes temporary paralysis or weakness

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14
Q

Disorders of muscle membranes (channelopathies) Myotonic dystrophy characterised by

A

Abnormal resting membrane potential

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15
Q

Congenital Myopathies: Definition

A

Myopathies that are present at birth or begin during infancy

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16
Q

Congenital Myopathies: Transmission

A

Usually hereditary and progress slowly

17
Q

Congenital Myopathies: Characterised by

A

Specific morphologically abnormalities that cause muscle weakness and loss of muscle tone in infancy and delayed motor development during childhood

18
Q

Diagnosis and investigation of muscle disease:

A
  1. DNA analysis
  2. Muscle biopsy
  3. Exercise testing
  4. Electromyography
  5. Plasma creatine kinase analysis
19
Q

DNA Analysis:

A
  1. Used to investigate disorders with major genetic component
  2. Single gene disorders (caused by mutation in one gene) are easiest to identify
  3. Possible to predict gene involved from the aberrant protein (e.g. dystrophin in DMD)
20
Q

Muscle Biopsy: Enzymes of glycolysis

A

Stain for enzymes involved in glycolysis e.g. PFK and myophospharylase → used to identify such as myophosphorylase defiency (McArdle’s disease)

21
Q

Muscle Biopsy: Storage Products

A

Periodic acid-Schiff Stains for Glycogen

Demonstrates abnormal glycogen storage in patients with glycogenesis

22
Q

Muscle Biopsy: Enzymes of oxidative metabolism

A

Oxidative enzymes e.g. NADH, cytochrome C oxidase, SDH used in diagnosis of mitochondrial myopathies
CCO used to demonstrate respiratory chain abnormalities
SDH used as marker enzyme for mito
→ Indicates abnormalities in mit distribution e.g. in mito myopathies, core disease, MD

23
Q

Ischaemic exercise disease: Used to investigate

A

Certain metabolic myopathies

24
Q

Ischaemic exercise disease: Process

A
  • Baseline blood sample taken at rest
  • Circulation of forearm occluded whilst subject exercises forearm for fixed time or t o exhaustion
  • Circulation restored, blood samples taken immediately after exercise and during recovery
  • Blood analysed for lactate and ammonia
25
Q

Ischaemic exercise disease: Failure to produce lactate

A

• Disorders of glycogen metabolism e.g. myophosphorylase defiency

26
Q

Ischaemic exercise disease: Impaired ammonia production indicative

A

Of myoadenylate deaminase defiency (MADD)

27
Q

Incremental/steady state exercise test: Aids

A

Diagnosis/assessment of mito myopathies

28
Q

Incremental/steady state exercise test: Process

A
  1. Baseline blood sample taken at rest
  2. Subject exercises at series of incremental loads on bicycle ergometer or treadmill
  3. At each load, blood samples taken for lactate analysis, further samples taken during recovery
29
Q

Incremental/steady state exercise test: Elevated lactate levels for

A

Given workload indicates increased conversion of pyruvate to lactate

30
Q

Electromyography:

A
  1. Intramuscular (needle) EMG used to investigate alterations in muscle activity as a result of disease
  2. Most commonly studied features are:
    a. Insertional activity
    b. Spontaneous activity
    c. MUAP characteristics
    d. Recruitment patterns
  3. EMG changes occur as a result of membrane disorders that affect excitability of cell membrane, or as result of marked atrophy or necrosis.
31
Q

Plasma Creatine kinase analysis:

A
  1. Plasma CK levels may rise temporailiy in healthy subjects in healthy subjects following eccentric exercise (as shown in figure)
  2. Elevated plasma CK levels indicate damage to muscle cell membrane, and are common feature of DMD.