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NYCC MSP > Non-Inflammatory Muscle Pathology > Flashcards

Non-Inflammatory Muscle Pathology Flashcards

1
Q

Widespread muscular necrosis is called ____

A

rhabdomyolysis

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2
Q

In terms of location, muscular necrosis can be ____ or ____

A

widespread or segmental (localized)

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3
Q

Cells around the outside of muscle cells that maintain the muscle cell are called ____

A

satellite cells

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4
Q

Explain the steps of segmental regeneration of muscle

A
  1. injury to m. fiber causes segmental disintegration of sarcoplasm
  2. macrophages accumulate & penetrate the basement membrane to phagocytose sarcoplasmic contents
  3. activated satellite cells proliferate forming myoblasts
  4. macrophages leave w/ debris
  5. myoblasts align in center of fiber and begin to fuse
  6. fiber continues to regenerate until normal (up to 6mo)
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5
Q

Name 3 non-inflammatory muscle pathologies

A
  • Rhabdomyolysis
  • Duchenne muscular dystrophy
  • Becker muscular dystrophy
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6
Q

What is the etiology of Rhabdomyolysis?

A

skeletal muscle trauma
(also side effect of statin drugs)

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7
Q

What happens to muscle in Rhabdomyolysis?

A

diffuse, widespread, varying degrees of necrosis & regeneration of muscle fibers

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8
Q

How long can Rhabdomyolysis last?

A

can be acute, subacute, or chronic (eg. exercise induced compartment syndrome)

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9
Q

What will a biopsy of Rhabdomyolysis show?

A

clusters of macrophages in and around muscle fibers
(sarcoplasmic contents poured into circulation)

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10
Q

What are the risk factors for Rhabdomyolysis?

A
  • Drugs: statins (eg. for hypercholesterolemia), cocaine, amphetamines
  • trauma (crushing inj), severe exertion
  • metabolic myopathies
  • alcoholism
  • heat intolerance/stroke
  • influenza (muscle soreness = cell lysis)
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11
Q

What are the clinical manifestations of Rhabdomyolysis?

A
  • swelling, tenderness, & ++ weakness in mm
  • fatigue
  • joint pain
  • diffuse muscular pain
  • ^creatinine kinase, K+, creatine in blood
  • myoglobinuria –> acute renal failure
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12
Q

Why might patients with Rhabdomyolysis present with joint pain?

A

Hilton’s law
not a joint problem, but shared innervation with involved muscles

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13
Q

How would Rhabdomyolysis affect urine?

A

Myoglobinuria (myoglobin dumped into urine) causing tea-coloured urine

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14
Q

What causes acute renal failure in patients with Rhabdomyolysis?

A

myoglobin dumped into urine damages kidneys

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15
Q

What are the possible treatments for Rhabdomyolysis?

A
  • early & aggressive hydration to prevent kidney damage
  • diuretics
  • address hyperkalemia & low blood Ca2+ levels
  • prognosis varies depending on extent of kidney damage
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16
Q

Are muscular dystrophies cureable?

A

No, they are progressive

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17
Q

What are the general muscle characteristics of muscular dystrophies?

A
  • fiber necrosis w/ regeneration (imbalanced)
  • progressive fibrosis (eventual loss of contractility)
  • infiltration by fatty tissue (marbling)
  • no inflammation
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18
Q

What form(s) of muscular dystrophy is/are seen in pediatric patients?

A

X-linked: Duchenne & Becker

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19
Q

What form(s) of muscular dystrophy is/are seen in adults?

A

Myotonic dystrophy

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20
Q

What is the etiology of Duchenne muscular dystrophy?

A
  • X-linked recessive inheritance (passed by mother)
  • Xp21 gene mutation = no dystrophin produced
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21
Q

What sex is primarily affected by Duchenne muscular dystrophy?

A

males
(only 1 X chromosome to mutate; not likely to survive to reproduce)

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22
Q

What is the function of dystrophin?

A
  • links sarcolemma (m. cell mem.)to muscle cell fibers
  • transfers force from fibers to membrane
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23
Q

Describe the pathogenesis of Duchenne muscular dystrophy

A
  • lack of dystrophin influences ^influx of Ca2+ (hypercontraction) & release of soluble m. enzymes (eg. creatine kinase) into serum
  • breakdown of sarcolemma –> necrosis & repair
  • progressive m. fibrosis
  • necrosis > repair
  • m. fibers replaced by fibrofatty CT
  • late stage: extrafusal fibers disappear
24
Q

Duchenne muscular dystrophy primarily affects ____ fibers, but ____ fibers are still numerous

A

extrafusal; intrafusal/spindle

25
Q

What are the clinical manifestations of Duchenne muscular dystrophy?

A
  • pseudohypertrophy of calves
  • ^serum creatine kinase
  • abnormal m. morphology in utero
  • developmental/intellectual delays by 2-3yrs of age
  • m. weakness by 3-4yrs (hips & shoulders initially)
  • toe walk; waddling gait
  • hyperlordosis & scoliosis
  • falling, difficulty running/jumping/stairclimbing & getting up from floor
  • GI issues (less motility; smooth m)
26
Q

What is pseudohypertrophy of the calves?

A

muscle fibers replaced by fibrofatty CT in calves, causing appearance of hypertrophied calf muscles
(Duchenne MD)

27
Q

Where does muscle weakness begin in Duchenne muscular dystrophy?

A

Pelvic (hip) and shoulder regions

28
Q

What are the typical outcomes of Duchenne muscular dystrophy?

A
  • wheelchair bound by age 10
  • bedridden by age 15
  • death occurs due to respiratory insufficiency (diaphragm) or cardiac arrhythmia by age 20
29
Q

What is the etiology of Becker muscular dystrophy?

A

truncated dystrophin protein

30
Q

How does Becker MD compare to Duchenne MD?

A
  • lower quality rather than absent dystrophin
  • milder & later onset (better neural function)
31
Q

What are the clinical manifestations of Becker muscular dystrophy?

A
  • exercise intolerance (m. cramping)
  • rhabdomyolysis
  • myoglobinuria
32
Q

Name 3 congenital myopathies

A
  • central core dz
  • rod myopathy
  • central nuclear myopathy
33
Q

Congenital myopathies are also called ____

A

“floppy baby/child syndromes”
(don’t develop head control)

34
Q

What is the primary symptom of congenital myopathies?

A

hypotonia
- decreased DTRs
- decreased m. volume

35
Q

Name an example of a condition with severe hypotonia that results in death within the first year of life

A

Spinal muscular atrophy (Werdnig-Hoffman Dz)

36
Q

What is the 2nd most common lethal autosomal recessive condition?

A

Spinal muscular atrophy

37
Q

What is the most common lethal autosomal recessive condition?

A

cystic fibrosis

38
Q

What is the etiology of Central core disease?

A

chromosome 19 mutation of gene coding for ryanodine receptors
(autosomal dominant)

39
Q

What is the function of ryanodine receptors (RyR)?

A

help control Ca2+ release from SR

40
Q

Central core disease primarily affects ____ fibers

A

type I (slow twitch)

41
Q

How do biopsied muscle fibers appear in Central core disease?

A
  • involved fibers show central area of degeneration
  • may resemble fibers in denervating conditions, but no associated denervation present
42
Q

Central core disease puts individuals at higher risk for ____

A

malignant hyperthermia

43
Q

What are the clinical manifestations of Central core disease?

A

children will become ambulatory but have less than normal muscle strength

44
Q

What is malignant hyperthermia?

A
  • spike in body temperature occurs after anesthesia
  • Rhabdomyolysis or m. damage results from ^Ca2+ release through mutated RyR in SR
45
Q

How is Malignant hyperthermia treated in patients with Central core disease?

A

dantrolene (binds to RyR)

46
Q

What is the etiology of Rod myopathy?

A
  • various mutations, most commonly affecting Nebulin (connects z-line to actin)
47
Q

Describe the pathogenesis of Rod myopathy

A
  • rod-like inclusions arise from Z-band and accumulate in sarcoplasm
  • inflammation & denervation not present
  • non-progressive
48
Q

What are the clinical manifestations of Rod myopathy?

A
  • hypotonia
  • delayed motor milestones
  • secondary skeletal changes (kyphoscoliosis)
  • may involve mm of face, pharynx, neck
  • m. degeneration (late onset)
  • ^serum creatine kinase
49
Q

What causes scoliosis in congenital myopathies?

A

lack of postural tone

50
Q

What is the best indicator of muscular breakdown on lab findings?

A

^serum creatine kinase

51
Q

What is the etiology of Central nuclear myopathy?

A

autosomal recessive or dominant mutations of dynamin 2

52
Q

What are the clinical manifestations of Central nuclear myopathy?

A

facial & extraocular involvement (bilateral ptosis)

53
Q

What is ptosis?

A

drooping of upper eyelid

54
Q

What is the function of dynamin 2?

A

endocytosis, membrane function & actin assembly

55
Q

Describe the histologic appearance of Central nuclear myopathy?

A

single, centrally located nucleus in skeletal m cells

56
Q

Central nuclear myopathy primarily affects ____ fibers

A

type I

NYCC MSP (44 decks)

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