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11. CP - Diseases of the musculoskeletal system > (58) Diseases of the musculoskeletal system 2 > Flashcards

(58) Diseases of the musculoskeletal system 2 Flashcards

1
Q

Name the muscle fibre components

A
  • basal lamina
  • plasma membrane
  • mitochondria
  • sarcoplasmic reticulum
  • myofibrils
  • myonuclei
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2
Q

What is a sarcomere?

A

Basic unit of striated muscle tissue

Muscle fibers are composed of tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands

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3
Q

What is a myofibril?

A

A basic rod-like unit of a muscle cell. Muscles are composed of tubular cells called myocytes, known as muscle fibers in striated muscle, and these cells in turn contain many chains of myofibrils

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4
Q

What is the sarcoplasmic reticulum?

A

A specialised type of smooth ER that regulates the calcium ion concentration in the cytoplasm of striated muscle cells

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5
Q

What are the functional systems in muscle?

A
  • ion fluxes
  • neuromuscular transmission
  • excitation-contraction coupling
  • oxidative phosphorylation
  • mRNA transport
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6
Q

What types of stains are used?

A
  • H&E
  • NADH
  • COX
  • ATPase
  • Gomori Trichrome
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7
Q

What is dystrophin

A

A rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. This complex is variously known as the costamere or the dystrophin-associated protein complex

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8
Q

What are the general symptoms of muscle diseases?

A
  • wasting
  • pain
  • cramping
  • fasciculations
  • weakness
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9
Q

What are the clinical investigations into muscle disease?

A
  • clinical examination (neurological)
  • electromyograph
  • nerve conduction studies
  • MRI
  • serum/blood investigations
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10
Q

Muscle diseases can be divided into which 3 categories?

A
  • neurogenic muscle disease
  • motor end-plate disorders
  • primary muscle disease (myopathies)
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11
Q

Primary muscle disorders (myopathies) can be further divided into what?

A

Destructive or non-destructive depending on whether the muscle in necrotic or not

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12
Q

Which muscle are common sites for biopsy?

A
  • quadriceps
  • deltoid
  • biceps
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13
Q

Which muscles are common sites for needle biopsy and the most commonly biopsied?

A

Quadriceps

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14
Q

Name 4 types of disease pattern on muscle biopsy

A
  • neurogenic atrophy
  • myopathic
  • dystrophic
  • inflammatory
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15
Q

What is the sarcolemma?

A

Cell membrane of striated muscle fibre cell (basal lamina and plasma membrane)

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16
Q

What are the features of the basal lamina?

A
  • links muscle fibres to endomyseal connective tissue
  • survives muscle fibre necrosis
  • acts as platform for satellite cell proliferation
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17
Q

Name 3 diseases of the basal lamina

A
  • primary merosin deficiency
  • secondary merosin deficiency (Schwartz-Jampel syndrome)
  • integrin VII deficiency (limb girdle syndrome)
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18
Q

Name 4 diseases of the plasma membrane

A
  • dystrophin (duchenne muscular dystrophy)
  • sarcoglycans (limb girdle muscular dystrophy)
  • dysferlin (LGMD type 2B, miyoshi myopathy)
  • caveolin (LGMD type IC, rippling muscle disease)
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19
Q

What are the features of 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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20
Q

Name 2 defects of nuclear membrane-related proteins (emerins, lamina A/C)

A
  • limb girdle muscular dystrophy 1B

- emery-dreifuss muscular dystrophy

21
Q

Name a centronuclear myopathy

A

Myotubular myopathy

22
Q

What are the features of Emery-Dreifuss muscular dystrophy?

A
  • X-linked recessive
  • weakness or proximal arm and distal leg muscles
  • early contractors
  • cardiomyopathy
23
Q

What are the features of core disease?

A
  • not usually detected until child has started walking
  • dominantly inherited
  • central core is a well demarcated zone in the centre of a muscle fibre, devoid of normal histochemical reactivity (NADH-Tr)
  • cores only occur in type 1 fibres
24
Q

What are the features of nemaline myopathy?

A
  • presents with generalised neonatal hypotonia
  • respiratory insufficiency
  • high arch palate
  • kyphoscoliosis
  • autosomal recessive
25
Q

What are the features of malignant hyperthermia?

A
  • abnormal susceptibility to certain inhalational anaesthetic agents
  • prolonged rise in intracellular calcium ions
  • rigid contractions and elevation in body temp
  • muscle biopsy changes mild and non-specific
26
Q

What is seen on biopsy in malignant hyperthermia?

A
  • moderate increase in central nuclei

- occasional fibres contain cores

27
Q

What are the features of myotonic dystrophy?

A
  • dominantly inherited
  • myotonia and progressive weakness of facial muscles
  • onset 20-30 years
  • cardiac conduction defects
28
Q

What is seen on histology in myotonic dystrophy?

A
  • selective atrophy of type 1 fibres
  • type II hypertrophy
  • paucity of type IIb fibres
  • central nuclei are an early feature
  • motheaten and targetoid fibres
  • ring fibres common
29
Q

What are the features of facioscapulohumeral dystrophy?

A
  • dominantly inherited
  • also affects myocardium
  • present early in adult life
  • associated with progressive deafness
  • retinal vasculopathy
30
Q

What is seen on histology in 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
31
Q

Name 2 developmental disorders

A
  • X-linked myotubular myopathy

- congenital fibre-type disproportion

32
Q

Name the disorders of catabolic mechanisms

A
  • lysosomal disorders (-alpha glucosidase deficiency syndrome, - LAMP-2 deficiency, - X-linked myopathy with excessive autophagy)
  • proteolytic disturbances (- calpain 3 deficiency)
33
Q

Name 4 neuromuscular transmission defects

A
  • neurogenic muscle disease
  • myasthenia gravis
  • Lambert-Eaton myasthenic syndrome
  • congenital myasthenic syndrome
34
Q

Name 3 types of neurogenic muscle disease

A
  • motor neurone disease (MND)
  • spinal muscular atrophy (SMA)
  • hereditary motor and sensory neuropathies (HMSN)
35
Q

What are the features of myasthenia gravis?

A
  • autoimmune disease with antibodies usually IgG, against the acetylcholine receptor
  • muscle biopsy NOT an appropriate test
  • see mild changes of denervation atrophy
36
Q

What are the features of Eaton-Lambert myasthenic syndrome?

A
  • antibodies against presynaptic voltage-gated calcium channels in the neuromuscular junction
  • rare non-metastic manifestation of malignancy, usually oat-cell carcinoma of the bronchus
  • no specific changes in muscle biopsy
37
Q

What are the types of myopathies affecting fuel and energy metabolism?

A
  • selected disorders of carbohydrate metabolism
  • defects of fatty acid metabolism
  • respiratory chain defects (mitochondrial myopathies)
  • myoadenylate deaminase deficiency
38
Q

What is seen on histology in 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
39
Q

What are the immune and infectious myopathies?

A
  • dysimmune myopathies
  • polymyositis and dermatomyositis
  • inclusion body myositis
  • viral myositis
  • bacterial myositis
  • fungal, protozoal and other infections
40
Q

What is dermatomyositis?

A
  • inflammatory myopathy responsible for chronic debilitating disease
  • associated with scaly rash
41
Q

What is seen on histology nn dermatomyositis?

A
  • mononuclear cell infiltration of muscle with fibre necrosis and replacement fibrosis
  • inflammation predominantly perimysial where B cell predominate
  • in endomysium T4 cell predominate
  • MAC-deposition (C5-9) can be detected by IHC indicating hum oral antibody-dependent mechanism is mediated by complement
42
Q

What is the most severe drug-induced myopathy?

A

Acute necrotising myopathy causing rhabdomyolysis, myoglobulinaemia, and renal failure (heroin, ecstasy)

43
Q

What is the most common drug-induced myopathy?

A

Steroid-induced (type II fibre atrophy, increase in lipid droplets)

44
Q

Other than heroin, ecstasy and steroids, what other drug can cause myopathy?

A

Statins

45
Q

What are the effects of chronic denervation and disuse?

A

Denervation = spinal muscular atrophy, motor neuron disease

Disuse = plaster cast

46
Q

What are the features of motor neurone disease?

A
  • progressive disease of middle to old age
  • characterised by widespread degeneration of motor neurone
  • involves anterior horn cells, brain stem nuclei and Betz cells
  • upper and lower motor neurone signs with wasting associated with spasticity and brisk reflexes
47
Q

Which hormones of endocrine disorders can cause myopathy?

A
  • glucocorticoid
  • thyroid
  • parathyroid
  • growth hormone
  • insulin
48
Q

Name other miscellaneous myopathies

A
  • cancer-related muscle disease
  • effects of ageing
  • hereditary inclusion body myopathy
  • marinesco-sjorgen syndrome
  • osteomalacia myopathy
  • vitamin E deficiency
  • amyloid myopathy
  • rare myopathies of childhood

11. CP - Diseases of the musculoskeletal system (4 decks)

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