Peripheral Nerve & Skeletal Muscle Part 1 Flashcards

(37 cards)

1
Q

What is segmental demyelination?

What is a denuded axon?

What is a characteristic of the new myelination?

A

Primary involvement of Schwann cell & loss of myelin; no primary abn in axon
- Does not affect all Schwann cells (segmental)

Denuded axon is the stimulus for remyelination

Newly myelinated internodes are shorter than normal; concentric layers of Schwann cytoplasm and redundant BM surrounding thinly myelinated axon (onion bulbs)

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2
Q

What is denervation atrophy?

What is myopathy?

A

Follows loss of axon

Primary abnormality of muscle fiber itself

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3
Q

What is axonal degeneration?

What is denervation atrophy?

What are myelin ovoids?

A

Primary involvement of neuron & its axon; may be followed by axonal regeneration & reinnervation of muscle
- W axonal degeneration as muscle fibers in motor units lose input they will undergo denervation atrophy; atrophic fibers will become small and triangular

Schwann cells catabolize myelin & later engulf axon fragments producing small oval compartments

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4
Q

What is a traumatic neuroma?

A

Pseudotumor; outgrowing neurons can’t find their distal target so they become a haphazard whorled proliferation of axonal processes– painful

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5
Q

What is important to note about nerve regeneration and reinnervation of muscle?

A

Reinnervation of skeletal muscle changes its composition and the fiber type is determined by the neuron of the motor unit
- Normally there is a checkboard appearance as multiple neurons innervate a motor unit but as a neuron dies the living ones will innervate more of the fibers

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6
Q

What is type 2 fiber atrophy? (2)

A
  • Inactivity or disuse causes atrophy
  • Glucocorticoid therapy causes atrophy

Common in ICU settings– both disuse and steroids

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7
Q

What is segmental necrosis in a muscle fiber?

What does this signify as a disease process?

A

Destruction of a portion of myocyte followed by myophagocytosis (macrophages); loss of muscle fiber leads to deposition of collagen and fat
- This is an end-stage for everyone w muscle fiber loss, not unique to a certain type

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8
Q

What are the 4 pathological reactions of muscle fiber?

A
  • Segmental necrosis
  • Vacuolization, alterations in structural proteins or organelles, accumulation of intracytoplasmic deposits
  • Regeneration
  • Hypertrophy (muscle fiber splitting)
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9
Q

What do we see in regeneration of muscle fibers?

A

Regenerating portion has large internalizaed central nuclei; cytoplasm laden w RNA is red (trichrome stain)
- “Ragged red fiber”

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10
Q

What do we see with muscle fiber hypertrophy?

A

Response to an inc load either through exercise or pathologic condition
- Muscle fiber splitting: Large fibers may divide longitudinally; cross section = single large fiber w a cell membrane traversing its diameter often w adjacent nuclei

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11
Q

What do we see in axonal neuropathies?

Which axons are most susceptible?

What is the electrophysiological hallmark of axonal neuropathies?

A

Axons are the primary target ; growth cone regeneration begins at site of transection
- Degeneration & regeneration axons coexist in sinlge bx; w time, damage tends to outpace repair

Longest axons are most susceptible resulting in a “dying-back” type pattern of progression

EP hallmark: Reduction in single amplitude w relative preservation of conduction velocity

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12
Q

What do we see in demyelinating neuropathies?

What is the electrophysiological hallmark?

A

Schwann cells w their myelin sheaths are primary targets of damage, axons relatively spared
- New myelin sheaths are shorter and thinner

EP hallmark: Slowed nerve conduction velocity (myelin loss)

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13
Q

What do we see in neuronopathies? What can cause them?

What part of the body is affected?

A

Destruction of neurons w secondary degeneration of axonal processes

  • Can be d/t infections or toxins
  • Affect proximal and distal parts of body (whereas periph axonopathies affect only distal)
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14
Q

What is pain characteristic in peripheral neuropathy?

A

Tingling, stabbing, burning, “pins and needles”

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15
Q

Some characteristics of polyneuropathies?

A

Multiple nerves, usually symmetric

  • Start at the feet and ascend
  • Hand deficits same time as knee w “stocking & glove distribution”
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16
Q

What is mononeuritis multiplex?

A

Several nerves damaged in a haphazard fashion (multiple entities can cause it)
- Vasculitis is common cause of this pattern (polyarteritis nodosum)

17
Q

Some characteristics of polyradiculoneuropathies?

Is it symmetric? What part of the body do you see this affect?

A

Nerve root affected as well as peripheral nerves

- Diffuse symmetric in proximal and distal parts of body

18
Q

What is Bell’s Palsy?

What is a possible sx that could happen that doesn’t involve the face?

A

CNVII affected

One sided facial droop w possible facial tingling and ipsilateral limb paresthesia

19
Q

What is Guillain-Barre?

What sx do we see?

A

Acute inflammatory demyelinating polyneuropathy

  • Weakness beginning in distal limbs but rapidly advances; “ascending paralysis:
  • DTRs disappear early in disease process
  • Inflammation and demyelination of spinal nerve roots and peripheral nerves (radiculoneuropathy)
20
Q

What commonly precedes Guillain-Barre?

What pathogens do we commonly see?

A

Influenza-like illness or prior vaccination

- Often d/t campylobacter jejuni but can me CMV, EBV, mycoplasma pneumoniae

21
Q

What do we see histologically in GBS?

A

Perivenular & endoneurial infiltration by lymphs, macrophages, and plasma cells

  • Segmental demyelination affecting peripheral nerves
  • Anti-myelin antibodies
22
Q

What is the disease process of GBS?

What do we see in CSF?

A

Macrophages penetrate BM of Schwann cells esp in Nodes of Ranvier

Inc in CSF protein but inflammatory cells remain confined to the roots so little or no CSF pleocytosis

23
Q

Tx of GBS?

A

Plasmapheresis or IVIG if plasmapheresis is unavailable

Note: Will NOT respond to steroids

24
Q

What is chronic inflammatory demyelinating polyradiculoneuropathy?

How to differentiate from GBS?

Histo?

A

Symmetrical mixed sensorimotor polyneuropathy that persists for greater than 2 months

  • Relapses and remissions that evolve over years
  • T-cells and antibodies are affected

Clinical remission by immunosuppressive tx (Plasmapheresis or IVIG, steroids)

Ddx from GBS: Time course and response to steroids

Will see onion bulbs d/t recurrent demyelination and remyelination

25
What are 3 systemic autoimmune D/Os that could be a/w peripheral neuropathies?
RA, Sjogren, SLE Often take form of distal sensory or sensorimotor polyneuropathies
26
What is neuropathy a/w vasculitis and how does this often present? What markers do we commonly see?
Noninfectious inflammation of blood vessels that can involve & damage peripheral nerves - Often presents as mononeuritis multiplex MPO-ANCA and PR3-ANCA
27
What do we see happen to neurons in leprosy? What is the pathogen? What histo do we see? What sx are some sx?
Schwann cells invaded by Mycobacterium leprae; segmental demyelination & remyelination - Loss of both myelinated and unmyelinated axons - Symmetric polyneuropathy affecting cool extremities Histo: Endoneurial fibrosis & multilayered thickening of perineural sheaths Sx: Pain, loss of sensation, large traumatic ulcers
28
What kind of pattern neuropathy can early stage-HIV show?
Mononeuritis multiplex
29
What is it in diphtheria that attacks nerves? What sx?
Diphtheria endotoxin affects periph nerves beginning w paresthesia and weakness - Early loss of proprioception & vibratory sensation - Prominent bulbar & respiratory muscle dysfxn leading to death or long term disability Selective demyelination in anterior & posterior roots and into mixed sensorimotor nerves
30
Where does the varicella-zoster virus affect and what can we see in those areas?
Stays dormant in sensory ganglia w reactivation of latent inf causing painful vesicular eruptions in sensory dermatomes (shingles) - Often thoracic or trigeminal nerves Neuronal destruction w loss of affected ganglia; may show necrosis & hemorrhage Destruction of large motor neurons in anterior horns or cranial nerve motor nuclei
31
Characteristics of diabetic neuropathy?
Ascending distal symmetric sensorimotor polyneuropathy - Numbness, loss of pain, difficulty w balance - Paresthesias or dysesthesias - Ulcers leading to amputations - Diffuse vascular injury - ANS dysfxn leading to postural hypotension, incomplete bladder emptying, sexual dysfxn Loss of small myelinated fibers & unmyelinated fibers
32
Characteristics of uremic neuropathy?
Distal symmetric neuropathy and dec in DTRs
33
Characteristics of thyroid dysfxn neuropahty?
- Hypothyroidism leading to compression mononeuropathies (carpal tunnel) - Hyperthyroidism a/w Guillain-Barre like syndrome (rare)
34
What are some vitamin deficiencies that can lead to neuropathy?
- B1 (thiamine) - B6 (pyridoxine) - Folate - Copper - Zinc
35
What are some neuropathies a/w malignancy where we see direct infiltration or compression of peripheral nerves?
- Brachial plexopathy from neoplasm in apex of lung (pancoast tumor) - Obturator palsy (pelvic tumor), cranial nerve palsy from tumors at base of skull - Polyradiculopathy involving LE may develop cauda equina
36
What are some neuropathies a/w malignancy where we see paraneoplastic nauropathies? What are some patterns of the dysfxn?
Note: Often precede dx of underlying tumor - Sensorimotor neuropathy is most common and is r/t small cell lung cancer Sensory sx that start distally in an asymmetric and multifocal pattern
37
What are some neuropathies a/w malignancy where we see monocloncal gammopathies (B-cell neoplasms)? What does POEMS stand for?
- Tumors that secrete IgM a/w demyelinating periph neuropathy - IgG or IgA a/w peipheral neuropathy - Ig light chain may deposit amyloid POEMS - Polyneuropathy - Organomegaly - Endocrinopathy - Monoclonal gammopathy - Skin changes