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Clinical Pathology > Diseases of muscle > Flashcards

Diseases of muscle Flashcards

1
Q

What are the muscle fibre components?

A
  • Basal Lamina
  • Plasma membrane
  • Mitochondria
  • Sarcoplasmic reticulum
  • Myofibrils
  • Myonuclei
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2
Q

What functional systems are involved in control of muscle?

A
  • Ion fluxes
  • Neuromuscular transmission
  • Excitation-contraction coupling
  • Oxidative phosphorylation
  • mRNA transport
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3
Q

What symptoms might you see in muscle disease?

A 
Wasting
Pain
Cramping
Fasciculations
Weakness
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4
Q

What clinical investigations are used in muscle disease?

A
  • Clinical examination (neurological)
  • Electromyograph
  • Nerve conductions studies
  • MRI
  • Serum/Blood investigations
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5
Q

What is dystrophin?

A

Links the ECM with the actin cytoskeleton.

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6
Q

How might muscle disease be classified biologically?

A

Neurogenic muscle disease - problem with the nerve/spine/brain

Motor end-plate disorders

Primary muscle diseases - myopathies (destructive and non-destructive)

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7
Q

What is the basal lamina?

A
  • Links muscle fibres to endomyseal connective tissue
  • Survives muscle fibre necrosis
  • Acts as a platform for satellite cell proliferation
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8
Q

Which proteins may be deficient in dominant limb girdle muscular dystrophy?

A
  • Lamin A/C

- Caveolin 3

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9
Q

Which proteins may be deficient in recessive limb girdle muscular dystrophy?

A
  • Calpain 3
  • Dysferlin
  • a,b,g,d - sarcoglycan
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10
Q

Which proteins may be deficient in X-linked limb girdle muscular dystrophy?

A
  • Dystrophin (Duchenne, Becker)

- Emerin (Emery Dreifuss)

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11
Q

What is Duchenne Muscular dystrophy?

A
  • Sex-linked recessive disorder
  • Gene product - dystrophin
  • Relentlessly progressive wasting
  • Chair-bound by 12 years
  • Proximal muscle weakness
  • Hypertrophy of calves
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12
Q

What are diseases of myonuclear abnormalities?

A

Defects of nuclear membrane-related proteins (emerins, lamin A/C)

  • Limb girdle muscular dystrophy 1B
  • Emery-Dreifuss Muscular Dystrophy

Centronuclear myopathies
- Myotubular myopathy

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13
Q

What is Emery-Dreifus muscular dystrophy?

A
  • X-linked recessive
  • Weakness of proximal arm and distal leg muscles
  • Early contractures
  • Cardiomyopathy
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14
Q

What investigations are neccessary in limb-girdle musclular dystrophy and why?

A
  • Phenotypic overlap with spinal muscular atrophy and BMD
  • Histochemistry inadequate investigation
  • Need immunohistochemistry to exclude BMD and SMA
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15
Q

What is central core disease?

A
  • Not usually detected until child has started walking
  • Dominantly inherited
  • The central core is a well demarkated zone in the centre of a muscle fibre, devoid of normal histochemical reactivity (NADH-Tr)
  • Cores only occur in type I fibres
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16
Q

What is nemaline myopathy?

A
  • Present with generalised neonatal hypotonia
  • Respiratory insufficiency
  • High arched palate
  • Kyphoscoliosis
  • Autosomal recessive
17
Q

What is malignant hypothermia?

A
  • Abnormal susceptibility to certain inhalational anaesthetic agents
  • Prolonged rise in intracellular calcium ions
  • Rigid contractions and elevation in body temperature
  • Muscle biopsy changes mild & non-specific
18
Q

What is myotonic dystrophy?

A
  • Dominantly inherited
  • Myotonia and progressive weakness of facial muscles
  • Onset 20-30 years
  • Cardiac conduction defects
19
Q

What is the typical histopathology of myotonic dystrophy?

A
  • Selective atrophy of type I fibres
  • Type II hypertrophy
  • Paucity of type IIb fibres
  • Central nuclei are an early feature
  • Motheaten & targetoid fibres
  • Ring fibres common
20
Q

What is facioscapulohumeral dystrophy?

A
  • Dominantly inherited disorder
  • Also affects myocardium
  • Presents early in adult life
  • Associated with progressive deafness
  • Retinal vasculopathy
21
Q

What is the histology of facioscapulohumeral dystrophy?

A
  • Histological changes may be minimal
  • Scattered angular atrophic fibres
  • Little else is specific
  • Biopsy an affected muscle (Biceps or triceps) - Deltoid often preserved
22
Q

What are the disorders of catabolic metabolism?

A

Lysosomal disorders

  • Alpha glucosidase deficiency syndrome
  • LAMP-2 deficiency
  • X-linked myopathy with excessive autophagy

Proteolytic disturbances
- Calpain 3 deficiency

23
Q

What are the neurogenic muscle diseases

A
  • Motor neuron disease (MND)
  • Spinal muscular atrophy (SMA)
  • Hereditary motor and sensory neuropathies (HMSN)
24
Q

What is myasthenia gravis?

A
  • Autoimmune disease with antibodies, usually IgG, against the acetylcholine receptor
  • Muscle biopsy NOT an appropriate diagnostic test
  • See mild changes of denervation atrophy
25
Q

What is Eaton-Lambert Myasthenic syndrome?

A
  • Rare non-metastatic manifestation of malignancy, usually oat-cell carcinoma of the bronchus
  • No specific changes in the muscle biopsy
26
Q

What is mitochondrial myopathy?

A
  • Ragged red fibres
  • EM reveals these to represent whorled cristae or crystalline inclusions
  • Accumulation of lipid on Oil Red O stain
  • Biopsy may be relatively normal
27
Q

What is dermatomyositis?

A
  • Inflammatory myopathy responsible for chronic debilitating disease
  • Associated with a scaly rash
  • Mononuclear cell infiltration of muscle with fibre necrosis and replacement fibrosis
  • Inflammation predominantly perimysial where B cells predominate
  • In endomysium T4 cells predominate
  • MAC-deposition (C5-9) can be detected by IHC indicating that the humoral antibody-dependent mechanism is mediated by complement
28
Q

Give examples of drug-induced myopathies.

A
  • Statin myopathy
  • Steroid induced myopathy probably most common.
  • -Type II fibre atrophy
  • -Increase in lipid droplets
  • Most severe drug reaction is an acute necrotising myopathy causing rhabdomyolysis, myoglobinuria & renal failure
  • -Heroin
  • -Ecstasy
29
Q

What is motor neuron disease?

A
  • Characterised by widespread degeneration of motor neurons
  • Involves anterior horn cells, brain stem nuclei and Betz cells
  • Upper & lower motor neuron signs with wasting associated with spasticity & brisk reflexes

Clinical Pathology (65 decks)

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