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Pathophysiology - Neurology > Weakness and Neuromuscular Disease > Flashcards

Weakness and Neuromuscular Disease Flashcards

1
Q

What symptom indicates that their must be nerve involvement in a neuromuscular disease?

A

Any degree of sensory involvement

If the problem is motor only -> weakness could be due to a neuropathy or a myopathy

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2
Q

What are the features of weakness, sensory loss, reflex preservation, and atrophy in a myopathy?

A

Weakness - proximal > distal
Sensory loss - none
Reflexes - generally present early on
Atrophy - mild and late, from disuse

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3
Q

What are the features of weakness, sensory loss, reflex preservation, and atrophy in a neuropathy?

A

Weakness - distal > proximal
Sensory loss - distal
Reflexes - generally lost early on
Atrophy - generally early and marked

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4
Q

What is non-physiologic weakness?

A

I.e. giveaway weakness -> a conversion disorder where weakness is not neuromuscular but rather psychological

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5
Q

Give the 5 point scale for muscle strength. What is done special for one of these?

A

0 - no visible contraction
1 - visible contraction but no movement at joint
2 - Movement at joint but not against gravity
3 - Movement against gravity but not against resistance
4 - Less than normal, but more than antigravity. Special - physicians grade 4-, 4, or 4+ since this is such a wide range
5 - Normal

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6
Q

Give the 4 point scale for rating reflexes?

A 
0 - areflexia
1 - hyporeflexia
2 - normal
3 - hyperreflexia
4 - clonus - specify # of beats
5 - sustained clonus (some physicians use this)
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7
Q

How can you have areflexia in the absence of weakness?

A

Pure sensory neuropathy can take out the afferent limb of the reflex loop
-> sensory neuropathies can thus slightly reduce reflexes as well

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8
Q

What can be the causes of asymmetric or focal weakness?

A
  1. Myopathy affecting local muscles

2. Focal neuropathies, especially radiculopathies (affect spinal nerve root)

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9
Q

Are myopathies typically painful?

A

No. But if they are associated with inflammation (inflammatory myopathies, i.e. myositis) then they can be painful

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10
Q

Give several examples of how steroid hormones and thyroid hormone can contribute to endocrine myopathies.

A

Cushing’s syndromes - myopathy very common due to insulin resistance and atrophy

Addison’s disease - Myopathy which improves with steroids

Thyrotoxic (hyperthyroid) - overuse of muscle leads to muscle breakdown and possible rhabdomyolysis

Hypothyroid - Weakness and impairment of fast twitch muscle fibers

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11
Q

Give a couple other causes of endocrine myopathies than thyroid hormone and cortisol?

A
  1. Acromegaly - increased GH leads to abnormal muscle growth

2. Hypoparathyroidism - hypocalcemia -> tetany -> muscle breakdown

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12
Q

What are metabolic myopathies?

A

Abnormalities of muscle energy metabolism, including glycogen (glycogen storage diseases, this is all you’re getting), lipids, or mitochondrial

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13
Q

What are common lipid metabolism disorders which cause metabolic myopathy?

A

Primary carnitine deficiency
Carnitine palmitoyltransferase deficiency
Long chain acyl-CoA dehydrogenase deficiencies

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14
Q

How are mitochondrial myopathies usually inherited and what does biopsy show?

A

Can be transmitted through maternal inheritance only, although some mitochondrial enzymes are autosomal recessive and can be inherited this way

Biopsy shows “ragged red fibers” - accumulation of diseased mitochondria

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15
Q

Other than muscles, what other organ is commonly involved in mitochondrial myopathies and why?

A

CNS - often with “mitochondrial encephalopathy” as in MELAS or “myoclonic epilepsy” as in MERRF

-> neurons are preserved through lifespan and must deal with abnormal mitochondria throughout life

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16
Q

What drugs are associated with toxic myopathy? Include drugs causing myopathy with neuropathy, and drugs causing cardiomyopathy?

A

Myopathy with neuropathy - statins, fibrates, organophosphates, vincristine

Cardiomyopathy: doxorubicin, metronidazole (high dose in Crohn’s)

pg 241 of first aid

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17
Q

What drugs are associated with the “grand trio” of toxic myopathy: myopathy, cardiomyopathy, and neuropathy?

A

COLCICHINE, doxorubicin, chloroquine / hydroxychloroquine, fibrates, ethanol

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18
Q

What are important congenital myopathies?

A
  1. Central core disease
  2. Nemaline rod myopathy
  3. Myotubular myopathy
  4. Congenital fiber-type disproportion
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19
Q

What are the periodic paralyses also called and what channels are affected?

A

“Channelopathies”

Hyperkalemic periodic paralysis - Sodium channel gain-of-fuction, cannot be inactivated, leads to hyperkalemia in episodes of sudden weakness due to sustained contraction

Hypokalemic Periodic Paralysis - Calcium channel loss-of-function so contraction cannot be triggered -> periodic hypokalemic weakness periods

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20
Q

What physical exam finding is important in differentiating glycogen storage diseases?

A

Presence of hepatomegaly

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21
Q

What will venous lactate levels after exercise testing show in glycogenoses vs mitochondrial disease?

A

Glycogenoses, except Pompe’s disease -> deceased rise in blood lactate, as all available glucose is fully used, and no more can be broken down from glycogen

Mitochondrial disease - elevated blood lactate, as problems with oxidative phosphorylation force all energy generation via anaerobic glycolysis

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22
Q

What lab is elevated in myopathy which is more specific than CPK?

A

Aldolase

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23
Q

What will EMG (electromyography) show at rest vs. slight contraction vs maximal contraction in normal muscle?

A

Rest - no firing

Slight contraction - a few regular waveforms representing the twitching on few motor units

Maximal contraction - all motor units firing spontaneously generates a complete interference pattern

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24
Q

What will EMG (electromyography) show at rest vs. slight contraction vs maximal contraction in denervated muscle (neurogenic atrophy)?

A

Rest - fibrillation - denervated muscles produce extrajunctional ACh receptors and begin to fire randomly

Slight contraction - giant unit waves with high amplitude -> motor units are much larger on small firing due to “fiber type grouping”

Maximal contraction - reduced interference pattern -> fewer motor units fire

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25
Q

What will EMG (electromyography) show at rest vs. slight contraction vs maximal contraction in myopathy?

A

Rest - Fibrillation - fibers are still sick so they fire randomly

Slight contraction - small amplitude units - motor units innervate fewer fibers (muscle disease / atrophy)

Maximal contraction - full interference pattern, but lower amplitude than normal, due to loss of muscle fibers

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26
Q

What is myositis and what are its three broad causes? Which ones are usually localized vs systemic?

A

Inflammation of a muscle

  1. Infectious - localized or systemic
  2. Drug-induced - localized or systemic
  3. Autoimmune - always systemic
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27
Q

Give viral, bacterial, and parasitic causes of infectious myositis.

A

Viral - influenza / parainfluenza, coxsackievirus

Bacterial - S. aureus or S. pyogenes

Parasitic - T. spiralis, cysticercosis, toxoplasmosis

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28
Q

What are the two most common inflammatory myopathies (and are also a type of autoimmune myositis)?

A

Polymyositis

Dermatomyositis

29
Q

Which inflammatory myositis presents more acutely and is associated with systemic symptoms? What are its symptoms?

A

Dermatomyositis

  • erythematous dermatitis over upper trunk, neck, and extensor surfaces of fingers, elbows, and knees
  • heliotrope rash - purple discolatoration with periorbital edema
  • rash on fingers gives look of calloused ‘mechanics hands’ with nailbed infarcts
30
Q

What is seen in the serum in patients with dermatomyositis and how does this relate to treatment?

A

Circulating antibodies to myosin and nuclear antigens

-> plasmapheresis is a good treatment, more helpful in DM than PM

31
Q

What will EMG show for inflammatory myositis?

A

Irritative myopathy - resting state burst of activity on needle insertion -> muscle is very irritable and will fire on baseline needle insertion

32
Q

What will biopsy show for autoimmune myositis and how do you differentiate between dermatomyositis and polymyositis?

A

Both show segmental myonecrosis and regeneration with mononuclear inflammatory infiltrates -> CPK elevations

Dermatomyositis - vasculopathic changes

Polymyositis - CD8+ T cells

33
Q

What is the most typical treatment regimen for DM/PM?

A

Prednisone, which should be gradually tapered as symptoms improve.

  • > Add azathioprine, MTX, cyclosporin as needed
  • > rituximab if refractory
34
Q

What is a muscular dystrophy and what are the five most important ones (get trolled idiot)

A

Progressive myopathy which is genetically determined

  1. Duchenne
  2. Becker
  3. Facioscapulohumeral
  4. Oculopharyngeal
  5. Myotonic
35
Q

What is the genetic difference between Duchenne and Becker muscular dystrophy?

A

Duchenne - typically due to a frameshift mutation or nonsense mutation which leads to absent or truncated protein -> almost completely absent dystrophin so more severe

Becker - non-frameshift mutations, leading to reduced dystrophin or abnormal dystrophin, but still partially functional. Often due to exon deletions.

36
Q

What are the clinical features of Duchenne? Are there any CNS symptoms?

A

Patients present by age 5 with waddling gait due to pelvic girdle muscle weakness -> lordosis. Calf muscles shorten with pseudohypertrophy. Become wheelchair dependent by age 12. Cognitive impairment is common as dystrophin is needed for neuronal maintenance.

Death occurs due to respiratory compromise / infection / dilated cardiomyopathy

37
Q

What are the clinical features of Becker? Are there any CNS symptoms?

A

Adolescent onset -> most not wheelchair bound until age 16. No cognitive deficits, and less tendency to form contractures of muscle since breakdown is less severe.

38
Q

What is facioscapulohumeral dystrophy and what are the symptoms?

A

Autosomal dominant dystrophy, presents in adolescence with progressive facial weakness, and weakness of proximal upper and lower extremities.

39
Q

What is the treatment of choice for facioscapulohumeral dystrophy?

A

Scapular fixation to surgically improve arm abduction
-> patients will have scapular winging before this

Patients will also need dysphagia management

40
Q

What are the symptoms of oculopharyngeal dystrophy? Who typically gets it?

A

Autosomal dominant condition of French-Canadians, presents later in life.

Dysphagia (pharyngeal involvement) with progressive ptosis of eyelids

41
Q

What is the most common form of muscular dystrophy in adults? What causes it?

A

Myotonic dystrophy type 1

- expanded CTG repeat in DMPK gene

42
Q

What are the relevant symptoms of myotonic dystrophy type 1?

A

CTG - cataracts, toupee (frontal balding), gonadal atrophy

Myotonia - inability to relax muscles after vigorous effort - i.e. handshake
Muscular dystrophy
EKG changes - heart block leads to arrhythmias

43
Q

How do patients with myotonic dystrophy look? What is a common treatment required in this condition?

A

They have a “hatchet face” appearance -> muscle loss in temporal face + frontal balding makes face look elongated

Need for pacemaker is common -> PR interval elongation progresses to heartblock

44
Q

How are dystrophies typically diagnosed, and what is the treatment for Duchenne’s and muscular dystrophies in general?

A

Typically diagnosed clinically with elevated CPKs, confirmed by genetic testing for all of these.

Treatment - largely supportive -> i.e. Achille’s tendon contracture release in Duchenne due to fibrofatty change, pulmonary care, physical therapy, bracing

45
Q

What tends to be the distribution of hereditary neuropathies and what are some examples?

A

Symmetric or uniform distribution.
Examples:
-DNA repeat syndromes (Friedreich ataxia, spinocerebellar ataxias)
-Motor neuron diseases (hereditary ALS)
-Hereditary motor-sensory neuropathies (i.e. charcot-marie-tooth disease)

46
Q

What are some example causes of acquired neuropathies?

A

Autoimmune neuropathies - i.e. Guillain-Barre

Diabetic neuropathy

Endocrine neuropathies

Infections - hep C, diphtheria, chronic TB

Paraneoplastic neuropathy

Toxic neuropathy - lead, colcichine, vincristine/vinplastine

Nutritional

ALS

47
Q

What are some causes of nutritional neuropathies?

A

Vitamin deficiencies

B1 - dry beriberi - symmetrical peripheral neuropathy
B6 - important for neurotransmitter synthesis
B12 - subacute combined degeneration
E - posterior column and spinocerebellar tract demyelination

48
Q

What is Charcot-Marie-Tooth disease also known as? Is the myelin or axon defected?

A

Hereditary motor and sensory neuropathy (HMSN)
-> myelin or axon could be affected, depending on the subtype -> need to do nerve conduction studies or biopsy to confirm

49
Q

Do hereditary sensory neuropathies (HSN) affect the myelin sheath or the axon?

A

HSN I-V (all of them) affect the axon, not myelin sheath

50
Q

What is small fiber neuropathy and what are some common causes?

A

Degradation of small (C fibers) neurons

Most commonly: diabetes, but could be any other cause of neuropathies

51
Q

What are the clinical symptoms of small fiber neuropathies?

A

Pain -> cold, tingling, or pins and needles sensation can occur.

May cause persistent burning as well.

52
Q

What will lab testing of small fiber neuropathies show? How is it diagnosed?

A

Normal reflexes, strength, and EMG assuming it is only small fiber involvement (A-delta fibers are needed for reflex pathway)

-> skin biopsy is widely accepted technique for diagnosis, with special stains to quantify nerve fiber density

53
Q

Prior to EMG and more invasive studies, what clinical workup should be done for evaluating neuropathy?

A

Genetic testing if family history is positive, and examine family members if possible

Ask about alcohol and inhalant use / exposures

Chemistry panel with tests for syphilis, lyme disease, diabetes, and autoimmune causes of axonal neuropathy

54
Q

Why would SPEP be done in a neuropathy workup?

A

Serum protein electrophoresis

Look for specific antibodies / paraproteins -> commonly seen in autoimmune or paraneoplastic neuropathies

55
Q

Give an example schema of how a basic EMG tests neuronal velocity?

A

Stimulate near elbow, measuring latency from stimulation to impulse carry in the thenar muscles

Stimulate closer to wrist, measure the same thing.

Calculate the distance between stimulations, and divide by the difference in latency between the two spots -> gives a nerve conduction speed in m/s which can be compared to baseline

56
Q

What is an F-wave test and what are its advantages?

A

Stimulate a motor neuron very distally so the impulse is propagated up back towards the spinal cord. Impulse will travel back done through another motor neuron after it stimulates another anterior horn cell

  1. Long distance travelled -> can detect any loss of speed or demyelination if there is any
  2. Impulse needs to travel through nerve root -> can detect radiculopathy
57
Q

What is the most consistent way to diagnose a neuropathy and why is it infrequently done?

A

Nerve biopsy -> need to destroy a sensory nerve which is very invasive and makes patient lose sensation

58
Q

What is the most common adult form of motor neuron disease? What neurons does it affect? Is there sensory involvement?

A

Amyotrophic lateral sclerosis
-> Affects both upper (lateral corticospinal tract) and lower motor neurons (anterior horn), although some variants may affect only UMN

There is NO sensory involvement

59
Q

How do patients present with ALS? Is bowel / bladder dysfunction common?

A

Any combination of UMN and LMN weakness involving limbs / bulbar innervated muscles -> can cause swallowing / voice problems

It is asymmetrical.

Bowel / bladder dysfunction is relatively rare until late in the disease -> sphincters are spared

60
Q

What is the most common familial ALS mutation, and what is the most common cause overall?

A

Familial ALS - superoxide dismutase 1 (SOD1) -> leads to free radical injury of neurons

-> overall, usually idiopathic

61
Q

What degenerates in Spinal Muscular Atrophy (SMA)? Is it common?

A

Symmetrical degeneration of anterior horn cells leading to muscle weakness and wasting of voluntary muscles

Second most common lethal autosomal recessive disease in Caucasians, after CF. So pretty common

62
Q

How is SMA categorized? Which one is most severe?

A

Based on age of onset and severity

Most severe: infantile form (SMA I) called Werdnig-Hoffmann disease, presents a floppy baby with fasciculations

Least severe form is SMA III: Kugelberg-Welander, adolescent onset

63
Q

What gene is defective in SMA?

A

SMN1 - survival motor neuron
SMN2 activity is very similar and can be modulated to make SMN1 protein product via a new medication

Many Werdnig Hoffmann patients are missing neuronal apoptosis inhibitory protein (NAIP) which is nearby

64
Q

What is Werdnig-Hoffman disease similar to? What’s the difference?

A

Similar to poliomyelitis. Difference is that polio occurs due to infection and causes an asymmetrical LMN degeneration, while SMA I causes a symmetrical degeneration

65
Q

What is the usual age of onset of ALS?

A

Usually in range of 40-70 years, with peak diagnosis in the 50s.

66
Q

What is the most important test in diagnosis of ALS to rule out other spinal cord lesions?

A

MRI of brain and spinal cord to exclude other causes of upper and lower motor neuron findings

67
Q

What therapy is specifically indicated for ALS and what is its mechanism of action?

A

Riluzole - prolongs life in ALS by 4-6 months
-think RiLOUzole as in Lou Gehrig’s disease

-Mechanism of action: anti-glutamate

68
Q

What signals the end stage of ALS? How are they kept alive?

A

Bulbar involvement (pharyngeal and laryngeal muscles affected) - life expectancy is less than 2 years after this onset

-> patients must be kept alive with tracheostomy and ventilatory support, and many ultimately become locked in

Pathophysiology - Neurology (21 decks)

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