Ch 27 - Neurodiagnostics Flashcards

1
Q

Name the following parts of a motoneuron

A

1 - motor neuron
2 - Ventral nerve root
3 - Spinal nerve
4 - Plexus
5 - motor nerve fibre
6 - NMJs
7 - muscle fibre

(A - sensory nerve fibre, B -spinal ganglion, C - Dorsal nerve root)

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2
Q

What is the difference between the myofibre-type composition of motor units and muscles?

A
  • Motor units have homogenous myofibre types
  • Muscles have a mixture of myofibres/motor unit types
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3
Q

What are the three categories of clinical signs of neuromuscular disorders?

A
  • Generalisaed or localised muscle weakness
  • Functional manifestations (paresis, weakness, regur, dysphagia etc)
  • Physical manifectations (atrophy, hypertrophy, skeletal deformities)
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4
Q

What are the principle signs of autonomic neuropathy?

A
  • Anisocoria or mydriasis
  • Decreased tear secretion
  • Decreased saliva
  • Bradycardia
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5
Q

What is required in a minimum database specific for NMD

A
  • CK
  • Electrolytes
  • Lactate
  • Urinalysis for myoglobinuria
  • Thyroid screening
  • Serum ACh-Receptor Ab
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6
Q

How do you interpret CK in regards to NMD?

A
  • Large elevations over 10,000 may be assoc with muscular dystrophies, necrotising myopathies and inflammatory myopathies
  • Mild-to-mod elevations may be seen with inflammatory myopathies and in some degenerative myopathies
  • Mod-to-marked elevations in anorectic cats
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7
Q

What inherited genetic disease may show abnormalities on electrolytes?

A

Hyperkalaemic and hypokalaemic periodic paralysis

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8
Q

How can you distinguish myoglobinuria from haemoglobinuria?

A

ammonium sulfate precipitation test

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9
Q

What are the 2 main specific tests for NMD?

A
  • Electrodiagnostic testing
  • Muscle and nerve biopsies
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10
Q

What is electromyography?

A
  • The detection and characteristion of electrical activity (potentials) recorded from a patients muscles
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11
Q

List the 4 types of normal spontaneous muscle activity which can be seen on electromyography

A
  • Insertional activity - stimulated by insertion of the needle
  • Miniature end-plate potentials - when needle is in close proximity to NMJ
  • End-plate spikes - a single, normal myofibre depolarises completely
  • Motor unit action potentials - normal muscle which is not completely at rest
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12
Q

List the three forms of abnormal spontaneous activity seen on electromyography

A
  • “Fibs” and “Sharps” - spontaneously firing, hypersensitive, single myofibers as a result of destabilisation of the sarcolemmal membrane
  • Complex repetitive discharges - polyphasic waves of uniform frequency, configuration and amplituse. Due to spontaneous discharge of a myofiber and its surrounding myofibers in near synchrony.
  • Myotonic potentials - Waxing and waning frequencies
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13
Q

What are nerve conduction studies?

A

the recording and analysis of electrical waveforms of biologic origin elicited in response to electrical or physiologic stimuli

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14
Q

What nerves are most suitable for nerve conduction studies?

A

Fibular, tibial, ulnar and radial

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15
Q

How will decreased limb temperature effects conduction velocities?

A

decreased conduction velocity

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16
Q

What do cord dorsum potentials give us information about?

A
  • Sensory input to the spinal cord - useful with suspected nerve root avulsions
17
Q

Name two commonly encountered late responces during nerve conduction testing

A
  • F-wave - antidromic propagation
  • H-wave/reflex - electrically elicited stretch reflex
18
Q

Regarding repetitive nerve stimulation, what is the normal range of frequencies used for testing? What is considered a normal decremental response?

A
  • 0.5-50Hz
  • A small decremental response of less than 10% may be normal
19
Q

What is pseudofaciliation in repetitve nerve stimulation?

A

A normal response at very high stimulation (over 20Hz) in which there is in increase in amplitude with no change in area under the curve

20
Q

What are some criteria when selecting a muscle for biopsy?

A
  • Affected by the disease, but functional
  • Easily identified, minimal surgical approach with muscle fibres orientated in a single direction
  • Low morbidity
  • Previous interpretive experience
  • Remote to tendon insertions and aponeuroses
  • Free of artefacts
21
Q

What are the commonly chosen muscles for biopsy?

A
  • Lateral head of the triceps (distal third)
  • Vastus lateralis (distal third)
  • Cranial tibial (proximal third)
  • Temporalis muscles
22
Q

What muscle biopsy is recommended for congenital myaesthenis gravis?

A

external intercostal muscle, exhibiting decreased numbers of ACh receptors

23
Q

What are the two options for performing a muscle biopsy?

A
  • Percutaneous
  • Open
24
Q

What fixative is used for electron microscopy samples?

A

Glutaraldehyde (in sodium phosphate budder or 5% Karnovskys fixative)

25
Q

List the criteria when selecting a nerve biopsy

A
  • Affected by the disease
  • Easily biopsies with low morbidity
  • Has an estabilished normal
  • Innervates a muscle which is routinely biopsied

Common fibular nerve most common!

26
Q

What fixatives are used for nerve biopsies?

A
  • 10% formalin
  • 2.5% glutaraldehyde