Chapter 22: Peripheral Nerves and Muscles

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1

The two major functional elements of peripheral nerves.

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axonal processes and myelin sheaths

2

Neuropathies that are caused by insults that directly injure the axon.

axonal neuropathies

3

The term used to describe changes observed in axonal neuropathies.

Wallerian degeneration

4

The morphologic hallmark of axonal neuropathies.

a decrease in the density of axons

5

Neuropathies characterized by damage to Schwann cells or myelin with relative axonal sparing.

demyelinating neuropathies

6

The effect of demyelinating neuropathies on conduction velocity and amplitude.

slow conduction velocity but preserved amplitude

7

The term used to describe the discontinuous pattern of demyelination seen in demyelinating neuropathies.

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segmental demyelination

8

Peripheral neuropathies that:

  1. affect peripheral nerves in a symmetric, length-dependent fashion
  2. have a “stocking-and-glove” distribution
  3. are often encountered with toxic and metabolic damage

polyneuropathies

9

Peripheral neuropathies that:

  1. randomly affects individual nerves
  2. may result in wrist drop or foot drop
  3. are often caused by vasculitis

mononeuritis multiplex

10

Peripheral neuropathies that:

  1. involve a single nerve
  2. are most commonly the result of trauma or infection

mononeuropathy

11

A rapidly progressive acute demyelinating disorder affecting motor axons, resulting in ascending weakness that can lead to death from failure of respiratory muscles within days of onset of symptoms.

Guillain-Barré syndrome

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The most common peripheral neuropathy, characterized by symmetrical mixed sensorimotor polyneuropathy that persists for 2 months or more.

chronic inflammatory demyelinating polyneuropathy (CIDP)

13

The most common cause of peripheral neuropathy, usually developing with long-standing disease.

diabetes

14

A form of diabetic neuropathy characterized by changes in bowel, bladder, cardiac, or sexual function.

autonomic neuropathy

15

A form of diabetic neuropathy that usually manifests with asymmetric pain that can progress to lower extremity weakness and muscle atrophy.

lumbosacral radiculopathy

16

The most common form of diabetic neuropathy, which primary affects sensory axons, resulting in paresthesias and numbness.

distal symmetric sensorimotor polyneuropathy

17

Etiological categories of peripheral neuropathies. (6)

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  1. nutritional/metabolic
  2. toxic
  3. vasculopathic
  4. autoimmune
  5. infectious
  6. inherited
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An autoimmune disease with fluctuating muscle weakness that is caused by autoantibodies that target the neuromuscular junction.

myasthenia gravis

19

The most common antigenic target in myasthenia gravis.

postsynaptic acetylcholine receptor (AChR)

20

Most frequent clinical manifestations of myasthenia gravis.

ptosis (drooping eyelids) or diplopia (double vision)

21

A disease caused by autoantibodies that inhibit the function of presynaptic calcium channels, thereby reducing the release of acetylcholine into the synaptic cleft.

Lambert-Eaton syndrome

22

Carcinoma most commonly associated with Lambert-Eaton syndrome.

small cell lung carcinoma

23

A heterogeneous group of diseases that result from mutations that disrupt the function of various neuromuscular junction proteins.

congenital myasthenic syndromes

24

Exotoxin-producing bacteria associated with defects in neural transmission and muscle contraction. (2)

Clostridium tetani and Clostridium botulinum

25

A toxin that blocks the action of inhibitory neurons, leading to the increased release of acetylcholine and sustained muscle contraction and spasm.

tetanus toxin (tetanospasmin)

26

A toxin that inhibits acetylcholine release, producing a flaccid paralysis.

botulinum toxin

27

One lower motor neuron together with the associated axon, its neuromuscular junctions, and the skeletal muscle fibers it innervates.

motor unit

28

Two classifications of skeletal muscle fibers.

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slow twitch type I and fast twitch type II fibers

29

The complex of glycoproteins that couples the muscle cell sarcolemma to extracellular matrix proteins and the intracellular cytoskeleton

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dystrophin-glycoprotein complex (DGC)

30

Morphological change associated with both primary muscle diseases and secondary neuropathic changes.

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muscle fiber atrophy

31

The two main morphologic hallmarks of neurogenic muscle diseases.

grouped atrophy and fiber type grouping

32

Iatrogenic cause of focal or generalized muscle atrophy, which tends to affect type II fibers more than type I fibers.

prolonged disuse of muscles (e.g. bed rest, cast)

33

Pharmacological cause of muscle atrophy, which tends to affect proximal muscles and type II myofibers are affected preferentially in this setting.

glucocorticoids

34

Muscular disorder associated with progressive muscle injury in patients who have normal muscle function at birth.

muscular dystrophies

35

Progressive, early-onset muscular diseases associated with malformations of the central nervous system.

congenital muscular dystrophies

36

Present in infancy with muscle defects that tend to be static or to even improve with time, often associated with distinct structural abnormalities of the muscle.

congenital myopathies

37

The protein most commonly affected X-linked mutations in muscular dystrophies.

dystrophin

38

Two most important dystrophinopathies.

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Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD)

39

Dystrophinopathy that typically presents as clumsiness and an inability to keep up with peers because of muscle weakness.

Duchenne muscular dystrophy (DM

40

Dystrophinopathy that becomes symptomatic later in childhood or adolescence and progresses at a slower and more variable rate.

Becker muscular dystrophy (BMD)

41

The cardinal neuromuscular symptom in myotonic dystrophy.

myotonia

42

Protein most commonly affected by mutations in myotonic dystrophy.

dystrophia myotonica protein kinase (DMPK)

43

Term used to describe worsening of nucleotide repeat expansion diseases with each passing generation because of further trinucleotide repeat expansion.

anticipation

44

These muscular dystrophies preferentially affect the proximal musculature of the trunk and limbs.

limb-girdle muscular dystrophies

45

A genetically heterogeneous disorder caused by mutations affecting structural proteins found in the nucleus.

Emery-Dreifuss muscular dystrophy (EMD)

46

An autosomal dominant form of muscular dystrophy that is caused by complex genetic changes that allow expression of the transcription factor DUX4 that is normally repressed in mature tissues.

facioscapulohumeral dystrophy

47

A group of familial disorders caused by inherited defects in ion channels that are characterized by myotonia, hypotonic paralysis, or both.

ion channel myopathies

48

Results from mutations in the gene encoding the skeletal muscle sodium channel SCN4A, which regulates sodium entry during contraction.

hyperkalemic periodic paralysis

49

Triggered when patients carrying mutations in RYR1, a calcium efflux channel, receive halogenated anesthetic agents or succinylcholine during surgery

malignant hyperthermia

50

Myopathies caused by disorders of glycogen synthesis and degradation and lipid handling.

myopathies due to inborn errors of metabolism

51

Myopathies that stem from mutations in either the mitochondrial or nuclear genomes.

mitochondrial myopathies

52

A blotchy red appearance in special stains produces by aggregates of abnormal mitochondria in mitochondrial myopathies.

ragged red fibers

53

The traditional triad of inflammatory myopathies.

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polymyositis, dermatomyositis, and inclusion body myositis

54

An autoimmune disorder associated with increased expression of MHC class I molecules on myofibers and predominantly endomysial inflammatory infiltrates containing CD8+ cytotoxic T cells.

polymyositis

55

The most common inflammatory myopathy in children, often manifesting as a paraneoplastic disorder in adults, typically associated with skin manifestations.

dermatomyositis

56

The most common inflammatory myopathy in patients older than 60 years of age, characterized by the presence of rimmed vacuoles that contain aggregates of proteins that accumulate in neurodegenerative diseases.

inclusion body myositis

57

A cause of toxic myopathy thatmay take the form either of acute or chronic proximal muscle weakness, and it can be the first indication of thyrotoxicosis.

thyrotoxic myopathy

58

A cause of toxic myopathy that occurs after an episode of binge drinking, which may lead to acute renal failure secondary to myoglobinuria.

ethanol myopathy

59

A cause of toxic myopathy that most commonly occurs as a complication of statins (e.g., atorvastatin, simvastatin, pravastatin).

drug myopathy

60

Two forms of statin associated myopathy.

(1) toxicity of the drug and (2) statin-induced HMG-CoA reductase autoantibodies

61

Benign encapsulated tumors that may occur in soft tissues, internal organs, or spinal nerve roots.

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schwannomas

62

Cranial nerve most commonly affected by schwannomas.

vestibular portion of the eighth cranial nerve (vestibulocochlear nerve)

63

A hereditary condition most commonly associated with bilateral vestibular schwannomas.

familial neurofibromatosis type 2 (NF2)

64

Dense areas of schwannomas consisting of bland spindle cells with buckled nuclei are arranged into intersecting fascicles.

Antoni A

65

Loose, hypocellular areas of schwannomas consisting of spindle cells spread apart by a prominent myxoid extracellular matrix.

Antoni B

66

Benign peripheral nerve sheath tumors.

neurofibromas

67

Neurofibromas that arise as superficial nodular or polypoid tumors.

localized cutaneous neurofibromas

68

Neurofibromas that grow diffusely within the confines of a nerve or nerve plexus.

plexiform neurofibromas

69

Neurofibromas that are infiltrative proliferations that can take the form of large, disfiguring subcutaneous masses.

diffuse neurofibromas

70

An autosomal dominant disorder caused by mutations in the tumor suppressor neurofibromin, encoded on the long arm of chromosome 17 (17q).

neurofibromatosis type 1 (NF1)

71

Neoplasms seen in adults that typically show evidence of Schwann cell derivation and sometimes a clear origin from a peripheral nerve.

malignant peripheral nerve sheath tumors

72

A nonneoplastic proliferation associated with a previous injury leading to transection of a peripheral nerve.

traumatic neuroma