Ch 27 - Neurodiagnostics

Question 1

Name the following parts of a motoneuron

Answer 1

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)

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

What are the principle signs of autonomic neuropathy?

Answer 4

• Anisocoria or mydriasis
• Decreased tear secretion
• Decreased saliva
• Bradycardia

Question 5

What is required in a minimum database specific for NMD

Answer 5

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

Question 6

How do you interpret CK in regards to NMD?

Answer 6

• 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

Question 7

What inherited genetic disease may show abnormalities on electrolytes?

Answer 7

Hyperkalaemic and hypokalaemic periodic paralysis

Question 8

How can you distinguish myoglobinuria from haemoglobinuria?

Answer 8

ammonium sulfate precipitation test

Question 9

What are the 2 main specific tests for NMD?

Answer 9

• Electrodiagnostic testing
• Muscle and nerve biopsies

Question 10

What is electromyography?

Answer 10

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

Question 11

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

Answer 11

• 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

Question 12

List the three forms of abnormal spontaneous activity seen on electromyography

Answer 12

• “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

Question 13

What are nerve conduction studies?

Answer 13

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

Question 14

What nerves are most suitable for nerve conduction studies?

Answer 14

Fibular, tibial, ulnar and radial

Question 15

How will decreased limb temperature effects conduction velocities?

Answer 15

decreased conduction velocity

Question 16

What do cord dorsum potentials give us information about?

Answer 16

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

Question 17

Name two commonly encountered late responces during nerve conduction testing

Answer 17

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

Question 18

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

Answer 18

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

Question 19

What is pseudofaciliation in repetitve nerve stimulation?

Answer 19

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

Question 20

What are some criteria when selecting a muscle for biopsy?

Answer 20

• 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

Question 21

What are the commonly chosen muscles for biopsy?

Answer 21

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

Question 22

What muscle biopsy is recommended for congenital myaesthenis gravis?

Answer 22

external intercostal muscle, exhibiting decreased numbers of ACh receptors

Question 23

What are the two options for performing a muscle biopsy?

Answer 23

• Percutaneous
• Open

Question 24

What fixative is used for electron microscopy samples?

Answer 24

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

Question 25

List the criteria when selecting a nerve biopsy

Answer 25

• 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!

Question 26

What fixatives are used for nerve biopsies?

Answer 26

• 10% formalin
• 2.5% glutaraldehyde