Neurophys and neuromuscular disease

Question 1

NCS: Define and their use
- CMAP
- distal latency
- conduction velocity
- amplitude
- conduction block
- F-wave

Answer 1

compound muscle action potential
time for action potential to rise after stimulation
speed of conduction
vertical height of action potential
decay in amplitude due to demyelination
distal stimulation causes antidromic propagation to the spinal motor neurone - used to assess proximal nerve segments

Question 2

Features of NCS on for demyelinating lesions

Answer 2

slowed conduction velocity
conduction block (correlates with weakness)
Temporal dispersion
Lower amplitudes due to dispersion or conduction block

Question 3

Features of NCS for axonal lesions

Answer 3

Low amplitudes due to loss of axons

Question 4

NCS in Carpal Tunnel

Answer 4

median nerve
sensory studies most sensitive and earliest affected
increasing severity: sensory conduction slowed then reduced size of amplitude

Question 5

Radial neuropathy

Answer 5

usually painless wrist and finger drop, usually due to compression at radial groove

Question 6

EMG definitions
- motor unit potential
- motor unit potential duration
- motor unit potential amplitude
- recruitment

Answer 6

sum of all muscle fibre action potentials
total number of muscle fibres in motor unit
reflects density of muscle fibres in one motor unit
assesses number of functional motor units in relation to generated force: early in myopathy, reduced in neuropathy

Question 7

Motor neurone disease
mode of inheritence

Answer 7

rarely inherited, usually sporadic