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Neuropathology > Neuromuscular Disease > Flashcards

Neuromuscular Disease Flashcards

1
Q

PNS

Somatic components

Aff/eff limbs

A 
Aff
DRG 
Peripheral sensory receptors
Peripheral nerve
Dorsal roots
Eff
Lower motor neuron
Skeletal muscle fibers:
extrafusal fibers
intrafusal fibers (muscle spindle)
Peripheral nerve
Ventral roots
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2
Q

PNS

Visceral components

A

Autonomic:

SS ganglia and nerves
PS ganglia and nerves
Eneteric plexus

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3
Q

Muscle groups

Units defined by CT

list

A

Epimysium = muscle

Perimysium = fascicle

Endomysium = myocytes

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4
Q

Skeletal muscle

Important cytoplasmic structures

A

myofibril: chains of contractile proteins arranged in sarcomeres
sarcomere: unit of contractile protein (Z band to Z band)

T tubule: calcium channeling system

sarcolemma: external cell membrane containing specialized proteins

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5
Q

NMJ

def

A

innervation point of muscle cell

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6
Q

Comparison of muscle fiber types in normal muscle

Type 1 vs type 2

Chicken meat/function

A

Type 1
Chicken meat: Red (more myoglobin)
Function: Sustained work (non-fatigable)

Type 2
Chicken meat: White (more glycogen)
Function: Sporadic work (fatigable)

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7
Q

Comparison of muscle fiber types in normal muscle

Type 1 vs type 2

Physiologic response/size/metabolism

A

Type 1
Physiologic response: Slow twitch
Size: Smaller
Metabolism: Oxidative

Type 2
Physiologic response: Fast twitch
Size: Larger
Metabolism: Mixed (2A), glycolytic (2B)

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8
Q

Comparison of muscle fiber types in normal muscle

Type 1 vs type 2

Mitochondria/glycogen content/lipid content/capillary density/ ATPase stain (pH 9.4)

A 
Type 1
Mitochondria: Many
Glycogen content: Low
Lipid content: High
Capillary density: High
ATPase stain (pH 9.4): Light
Type 2
Mitochondria: Few
Glycogen content: High
Lipid content: Low
Capillary density: Low
ATPase stain (pH 9.4): dark
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9
Q

Muscle

Dependence on innervation

A

muscle is dependent on its innervation for voluntary contraction and maintenance of myocyte size, fiber type, & function (trophic effect of nerve cell)

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10
Q

Motor unit

Consists of…

A

motor unit consists of the AHC and all muscle cells innervated by it: size varies based on degree of control necessary for muscle

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11
Q

Muscle

Fiber type/metabolism det’d by…

A

fiber type/metabolism is determined by the AHC: all muscle cells innervated by the same AHC have the same fiber type

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12
Q

Muscle spindle

Def/fun

A

muscle spindle: an encapsulated group of specialized muscle fibers (intrafusal fibers) with sensory and motor innervation: involved in primary myotatic reflex arc(“stretch reflex”) and maintenance of muscle tone

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13
Q

Muscle

Adaptation of muscle to training/work

A

strength training: fiber hypertrophy, primarily type 2

aerobic training: increased oxidative capacity of muscle

disuse leads to relative atrophy of type 2 fibers

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14
Q

LMN vs UMN

A
  1. lower motor neuron (AHC) or its axon: damage leads to flaccid (hypotonic) muscle paralysis followed by atrophy
  2. upper motor neuron (Betz cells in primary motor cortex and axons in corticospinal tract): damage leads to paralysis of voluntary movement; muscle is initially flaccid, then becomes spastic (hypertonic) due to imbalance of central reflexes; eventual muscle atrophy is due to disuse.
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15
Q

Peripheral nerve

Consists of…

A

peripheral nerve consists of bundles of myelinated and unmyelinated axons, collections of ganglion cells, and axon terminals and receptors, with their associated cells and connective tissues.

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16
Q

Peripheral nerve

Grouped by CT

A

Epineurium = whole nerve

Perineurium = nerve fascicle

Endoneurium = nerve fibers

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17
Q

Peripheral nerve

Important structural features

A

axon (axoplasm)

Schwann cell

myelin sheath: internode: myelin unit defined between two nodes of Ranvier node of Ranvier: axon segment between adjacent myelin sheaths

terminal/receptor: neuromuscular junction, sensory receptor

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18
Q

Nerve fiber

Classification by axon size

Class/size/conduction velocity/function

α-fibers
Aα fibers
γ-fibers
Aβ, Aδ
C fibers
A

Class
Size
Conduction velocity
Function

α-fibers
Myelinated larger (13-20u)
70-120 m/s
Extrafusal muscle fibers

Aα fibers
Myelinated larger (13-20u)
70-120 m/s
Vibration, position, light touch

γ-fibers
Smaller (2-8u)
5-30 m/s
Intrafusal muscle fibers

Aβ, Aδ
Smaller (2-12u)
5-70 m/s
Sharp pain, temperature, pressure

C fibers
Unmyelinated small (0.2-1.5u)
0.5-2 m/s
Pain, automatic

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19
Q

Neurogenic atrophy

def

A

Neurogenic atrophy of skeletal muscle: skeletal muscle dysfunction due to abnormalities in its innervation

20
Q

Neurogenic atrophy

Clinical manifestations/pathology

A

clinical manifestations: weakness, paralysis, atrophy

pathology: denervation of myocyte leads to atroph

21
Q

Fiber type grouping/group atrophy of muscle

def

A

ability of adjacent nerve terminals to sprout and renervate denervated myocytes leads to alteration in normal pattern of fiber typing: fiber type grouping

progression of denervating process leads to group atrophy or atrophy of whole fascicle or muscle

22
Q

Examples of neurogenic muscle disease

3

A

trauma to peripheral nerves or roots containing motor fibers

anterior horn cell (AHC) diseases
poliomyelitis (viral infection destroying AHC) amyotrophic lateral sclerosis (neurodegenerative disease)
hereditary spinal muscular atrophies (SMA)

peripheral neuropathies affecting motor nerves

23
Q

Myopathies

Dysimmune/infectious myopathies

Def/examples

A

Damage to muscle fibers assoc with inflammation:

Immune mediated diseases: polymyositis, dermatomyositis
Inclusion body myositis
Specific infections (trichinosis, viruses, bacteria)
Vasculitides

24
Q

Myopathies

Muscular dystrophies

Definitions and examples

A

Inherited defects in muscle membrane/ECM components

resulting in progressive muscle fiber damage:
dystrophinopathies (Duchenne/Becker muscular dystrophy) many others

25
Q

Myopathies

Ion channel/ion transport defects

Definitions and examples

A

malfunction of excitation/contraction coupling, usually due to rare genetic molecular defects, often produce myotonia (failure of relaxation of muscle following voluntary contraction)

26
Q

Congenital myopathies

Definitions and examples

A

rare inherited defects in muscle now classified according to class of molecular defect:

myofibrillar proteins: e.g., nemaline myopathy others

27
Q

Hereditary metabolic myopathies

Definitions and examples

A

inherited defects in energy or intermediary metabolism:

glycogen storage disease (myopathic types) 
mitochondrial myopathies 
fatty acid (“lipid-storage”) diseases
28
Q

Drug/toxic myopathies

Definitions/examples

A

muscle fiber damage due to effects of drug, toxin, hormone, etc.

statin myopathies
steroid myopathy…

29
Q

Clinical features associated with myopathies

A 
Reflect muscle damage and dysfunction:
symmetrical weakness, often proximal > distal muscles 
fatigability 
exercise intolerance 
muscle pain
abnormal muscle tone 
cramps 
myoglobinuria 
elevated CK 
hyperkalemia
30
Q

Myopathies

dx

A

Myopathies are usually characterized by structural abnormalities in muscle fibers that can be seen under the microscope. Many are now also diagnosed by genetic or molecular testing.

31
Q

Myofiber necrosis

Results in…

A

results in release of creatine phosphokinase (CK), myoglobin, potassium.

rhabdomyolysis: syndrome of acute massive muscle fiber necrosis, often characterized by prominent myoglobinuria, can lead to renal failure

32
Q

Myofiber Regeneration

A

myofiber regeneration (“basophilic fibers”) from proliferation and differentiation of stem cells (satellite cells) in muscle, follows necrosis

33
Q

Histopathologic changes char of myopathies

list
6

A 
Myofiber necrosis
Myofiber regeneration
Inflammation
Fibrosis
Structural abnormalities
Physiologic abnormalities
34
Q

Histopathologic changes char of myopathies

fibrosis

A

fibrosis (fibrous scarring) of endomysium

35
Q

Histopathologic changes char of myopathies

Structural abnormalities in myofibers

A

storage material (e.g., glycogen, lipid).

increased mitochondria: “ragged red fibers”

abnormalities in structure of sarcomeres, abnormal cytoplasmic inclusions, etc., (often characteristic for particular congenital, toxic, or drug-induced myopathies)
Histopathologic changes char of myopathies

36
Q

Physiologic abnormalities

A

selective atrophy of a fiber type

abnormal proportions of fiber types

37
Q

Polymyositis/dermatomyositis

Mechanism

A

Immune-mediated:

PM: autoinvasive CD8+ T cells attack muscle cells directly
DM: antibody- or immune complex-mediated
microangiopathy with secondary muscle damage

38
Q

Steroid myopathy

Forms/mech

A

forms: iatrogenic; endocrinopathy (Cushing’s disease)
mechanism: steroids probably impair of muscle protein/ carbohydrate metabolism due to insulin resistance and protein catabolism and cause selective atrophy of type 2 fibers.

39
Q

Muscular dystrophies

def

A

Definition: heterogeneous group of inherited progressive degenerative myopathies associated with muscle fiber loss and replacement by connective tissue (endomysial fibrosis)

  • dystrophinopathies (Duchenne-Becker): are the most common
40
Q

Wallerian degeneration

chars

A

Degeneration of axon distal to site of damage/transection

  • Myelin sheath disintegrates secondarily to axon loss
  • NOTE: transection of axon proximally may lead to death of nerve cell
  • Cord of residual Schwann cells (band of Bungner) persists at site of lost axon for a time after degeneration of the axon and can facilitate regrowth of axon
41
Q

Regeneration of peripheral nerves

A

Regrowth of axons along cords of residual Schwann cells: growth rate <2mm/day.

  • May be effective in restoring much of nerve function if connections are re-established
  • Aberrant regeneration may form a disorganized tumor-like mass of nerve fibers, Schwann cells and scar tissue (traumatic neuroma)
    Distal axonal degeneration (“dying back neuropathy”)

Slow loss of axons over time, usually involving longest axons and beginning distally

  • Distal end of axon may appear swollen (a form of neuroaxonal dystrophy)
42
Q

Segmental demyelination

A

Damage or loss of myelin internodes along length of axon/nerve

  • Schwann cells may remyelinate the axon, but remyelinated segments may not conduct as efficiently as normal segments
  • Progressive episodes of demyelination and remyelination produce onion bulb formations (concentric proliferation of Schwann cells and collagen around nerve fiber) leading to enlargement of nerve fascicle (“hypertrophic neuropathy”)
43
Q

Clinical manifestations of PN

How are PN classified

A

Neuropathies are classified by the type of nerve involved (motor, sensory, autonomic), the anatomic pattern of involvement, the clinical time course (acute, subacute, chronic), and whether the pathologic process appears to involve primarily the axon or the myelin sheath.

44
Q

Sx of peripheral neuropathies

A

a. loss of function: weakness, sensory loss, hyporeflexia/areflexia, impaired autonomic function, etc.
b. exaggerated/distorted function: pain, dysesthesias (abnormal sensations)
c. musculoskeletal deformities (kyphoscoliosis, pes cavus, etc.), especially when the PN is present during development

45
Q

Patterns of involvement in peripheral neuropathies

A

a. mononeuropathy: involvement of one nerve
b. mononeuropathy multiplex: involvement of several separate nerves, usually asymmetric and involving different areas of body
c. polyneuropathy: symmetric involvement of multiple nerves usually in particular regions: e.g., “stocking-glove pattern” in distal neuropathy

46
Q

Distinction between axonal and demyelinating neuropathies

How is it made

A

Distinction between axonal and demyelinating neuropathies can often be made with electrodiagnostic studies.

Neuropathology (29 decks)

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