Ch 27 - Neurodiagnostics Flashcards
Name the following parts of a motoneuron
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)
What is the difference between the myofibre-type composition of motor units and muscles?
- Motor units have homogenous myofibre types
- Muscles have a mixture of myofibres/motor unit types
What are the three categories of clinical signs of neuromuscular disorders?
- Generalisaed or localised muscle weakness
- Functional manifestations (paresis, weakness, regur, dysphagia etc)
- Physical manifectations (atrophy, hypertrophy, skeletal deformities)
What are the principle signs of autonomic neuropathy?
- Anisocoria or mydriasis
- Decreased tear secretion
- Decreased saliva
- Bradycardia
What is required in a minimum database specific for NMD
- CK
- Electrolytes
- Lactate
- Urinalysis for myoglobinuria
- Thyroid screening
- Serum ACh-Receptor Ab
How do you interpret CK in regards to NMD?
- 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
What inherited genetic disease may show abnormalities on electrolytes?
Hyperkalaemic and hypokalaemic periodic paralysis
How can you distinguish myoglobinuria from haemoglobinuria?
ammonium sulfate precipitation test
What are the 2 main specific tests for NMD?
- Electrodiagnostic testing
- Muscle and nerve biopsies
What is electromyography?
- The detection and characteristion of electrical activity (potentials) recorded from a patients muscles
List the 4 types of normal spontaneous muscle activity which can be seen on electromyography
- 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
List the three forms of abnormal spontaneous activity seen on electromyography
- “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
What are nerve conduction studies?
the recording and analysis of electrical waveforms of biologic origin elicited in response to electrical or physiologic stimuli
What nerves are most suitable for nerve conduction studies?
Fibular, tibial, ulnar and radial
How will decreased limb temperature effects conduction velocities?
decreased conduction velocity
What do cord dorsum potentials give us information about?
- Sensory input to the spinal cord - useful with suspected nerve root avulsions
Name two commonly encountered late responces during nerve conduction testing
- F-wave - antidromic propagation
- H-wave/reflex - electrically elicited stretch reflex
Regarding repetitive nerve stimulation, what is the normal range of frequencies used for testing? What is considered a normal decremental response?
- 0.5-50Hz
- A small decremental response of less than 10% may be normal
What is pseudofaciliation in repetitve nerve stimulation?
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
What are some criteria when selecting a muscle for biopsy?
- 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
What are the commonly chosen muscles for biopsy?
- Lateral head of the triceps (distal third)
- Vastus lateralis (distal third)
- Cranial tibial (proximal third)
- Temporalis muscles
What muscle biopsy is recommended for congenital myaesthenis gravis?
external intercostal muscle, exhibiting decreased numbers of ACh receptors
What are the two options for performing a muscle biopsy?
- Percutaneous
- Open
What fixative is used for electron microscopy samples?
Glutaraldehyde (in sodium phosphate budder or 5% Karnovskys fixative)
List the criteria when selecting a nerve biopsy
- 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!
What fixatives are used for nerve biopsies?
- 10% formalin
- 2.5% glutaraldehyde
