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Neurology > Myopathy > Flashcards

Myopathy Flashcards

1
Q

What is myopathy?

A

Primary disorder of muscle with gradual onset of symmetrical weakness

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2
Q

What characteristics point towards myopathy?

A 
Gradual onset of symmetrical proximal weakness- difficulty combing hair, climbing stairs
Specific muscle groups affected
Preserved tendon reflexes
No paraesthesia or bladder problems 
No fasiculations
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3
Q

What would a rapid onset of symptoms suggest?

A

A toxic, drug or metabolic myopathy

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4
Q

What does spontaneous pain at rest and local tenderness suggest?

A

Inflammatory myopathy

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5
Q

What does pain on exercise suggest?

A

Ischaemia or metabolic myopathy

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6
Q

What does oddly firm muscles (due to infiltrations with fat or CT) suggest?

A

Pseudohypertrophic muscular dystrophies

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7
Q

What types of myopathic disorders are there?

A 
Inflammatory myopathies
Muscular dystrophies 
Myotonic disorders
Congenital myopathies
Metabolic myopathies
Endocrine myopathies 
Drug induced/toxic
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8
Q

What are muscular dystrophies?

A

A group of genetic diseases with progressive degeneration and weakness of specific muscle groups. The primary abnormality is in the muscle membrane.

There may be unusually firm muscles - fat and CT infiltration

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9
Q

In muscular dystrophies, what can be found on histology?

A

Marked variation in size of individual muscle fibres

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10
Q

What is the most common type of muscular dystrophy?

A

Duchenne’s muscular dystrophy

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11
Q

In Duchenne’s MD, progressive proximal muscle weakness occurs from what age?

A

Approximately 4 years old

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12
Q

Does Duchenne’s MD usually affect males or females?

A

Male

The disorder is x linked recessive
2/3 cases inherited from mother, 1/3 due to new mutation

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13
Q

Duchenne’s is caused by a mutation to the gene for the protein…

A

Dystrophin - important in maintaining muscle fibre cell membrane

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14
Q

How does Duchenne’s typically present?

A 
Clumsy walking
Difficulty standing 
Waddling gait
Respiratory failure - weak diaphragm 
Scoliosis
Dilated cardiomyopathy 
Arrhythmias
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15
Q

What is Gower’s sign (seen in Duchenne’s MD) ?

A

Child uses arms to stand up from squatted position

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16
Q

What percentage of patients with Duchenne’s muscular dystrophy have intellectual impairment?

A

30%

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17
Q

In Duchenne’s muscular dystrophy, pseudohypertrophy can occur especially in the…

A

Claves

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18
Q

Muscle loss typically occurs where first (in Duchenne’s muscular dystrophy)?

A

In the thighs and pelvis followed by the arms

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19
Q

Most people with Duchenne’s muscular dystrophy are unable to walk by what age ?

A

12

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20
Q

Why might affected muscles look larger in Duchenne’s?

A

Increased fat content

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21
Q

Those with Duchenne’s muscular dystrophy have a high level of what in their blood?

A

Creatine kinase - more than 40x normal

22
Q

Is there any specific treatment for Duchenne’s muscular dystrophy?

A

No
Physical therapy, braces, corrective surgery may help with symptoms

Glucocorticoids can help to slow degeneration

23
Q

Those with weakness of breathing muscles in Duchenne’s may require…

A

Assisted ventilation

24
Q

What is Becker’s muscular dystrophy?

A

Presents similarly to Duchenne’s but with milder symptoms, later stage and with better prognosis

25
Q

What is the average life expectancy for someone with Duchenne’s?

A

26

26
Q

Does Becker’s muscular dystrophy involve dystrophin gene mutation (similarly to Duchenne’s)?

A

Yes = dystrophinopathies

No dystrophin - nonsense or frameshift mutation (Duchenne’s)

Misshapen protein -missense mutation (Becker)

27
Q

Duchenne’s and Becker’s muscular distrophy are x linked recessive disorders. Why can females be manifesting carriers ie show symptoms?

A

In females only 1 X chromosome gets expressed and the other is inactivated (random) in cell. Would expect half of female cells to have functioning dystrophin gene and half to have defective. These people are typically asymptomatic. If more cells end up with the defective gene, they can be manifesting characters.

28
Q

Is dystrophin expressed in heart muscle?

A

Yes

29
Q

What investigations can be done to diagnose Duchenne’s or Becker’s?

A

High CK
Mutations in dystrophin - DNA test
Muscle biopsy - stain for dystrophin

30
Q

What is facioscapulohumoral muscular dystrophy?

A

A disorder characterised by muscle weakness and wasting. Gets its name from muscles that are affected most often - face, around shoulder blades and upper arms.

31
Q

When do the signs and symptoms of FSHD usually appear?

A

12-14

Although onset and severity can vary widely

32
Q

How does FSHD typically first present?

A

Inability to puff out cheeks (facial muscles)

Difficulty raising arms over head

33
Q

What signs are normally present indicating FSHD?

A 
Weak muscles around eyes prevent them closing fully e.g when asleep
Ironed out expression of face
Scapula winging 
Foot drop 
Scoliosis
Horizontal clavicles
34
Q

What is the inheritance pattern of FSHD?

A

Autosomal dominant

35
Q

What are myotonic disorders?

A

They cause tonic muscle spasms (myotonia) and demonstrate long chains of central nuclei within muscle fibres in histology.

The commonest = myotonic dystrophy - has 2 major forms

36
Q

What are the 2 main types of myotonic dystrophy?

A

DM1

DM2

37
Q

What does myotonia mean?

A

Prolonged muscle contracture; not able to relax muscle at will

38
Q

What is the inheritance pattern of myotonic dystrophy?

A

Autosomal dominant

39
Q

What causes DM1?

A

A trinucleotide repeat disorder - CTG repeat at the end of DMPK (dystrophia myotonica-Protein Kinase) gene on chromosome 19

40
Q

What causes DM2?

A

A repeat expansion of the ZNF9 gene on chromosome 3

41
Q

Which is commoner and more severe, DM1 or DM2?

A

DM1

42
Q

How does DM1 typically present?

A 
Between 20-40 years old
Distal weakness(hand/ foot drop)
Weak sternomastoids
Myotonia - tonic spasms of muscle 
Facial weakness and muscle wasting give a long, haggard appearance
43
Q

How is DM2 different from DM1 (in terms of weakness)?

A

DM2 proximal weakness more prominent

44
Q

What are some general features of myotonic dystrophy?

A 
Myotonia
Weakness of arms and legs
Mild mental impairment 
Diabetes mellitus
Testicular atrophy
Cardiac involvement - heart block, cardiomyopathy 
Dysphagia 
Cataracts 
Male frontal balding
45
Q

What is an example of a metabolic myopathy?

A

McArdle’s disease - glycogen storage disorder

46
Q

How does McArdle’s disease present?

A

Muscle pain and weakness after exercise

47
Q

Acquired myopathies of late onset are often part of systemic disease for example…

A

Hyperthyroidism
Malignancy
Cushing’s
Hypo and hypercalcaemia

48
Q

What drugs can cause myopathy?

A 
Alcohol
Statins
Steroids
Chloroquine
Vincristine 
Cocaine
49
Q

What are some example of inflammatory myopathies?

A

Inclusion body myosoitis
Polymyositis
Dermatomyositis

50
Q

Describe polymyositis and dermatomyositis

A

Rare conditions characterised by insidious onset of progressive, symmetrical, proximal muscle weakness
Autoimmune mediated striated muscle inflammation (myositis)
Associated with myalgia and arthralgia
Muscle weakness may cause dysphagia, dysphonia and respiratory weakness

51
Q

What is dermatomyositis?

A

Myositis plus skin signs

52
Q

When considering myopathy, what tests should be done?

A 
ESR, CK, AST, LDH - may be raised 
EMG
Tests relevant to systemic cause e.g TFT 
Muscle biopsy
Genetic testing

Neurology (31 decks)

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