8 - Electrodiagnostics

Question 1

When do peripheral nerve fibers reach their maximum diameter?

Answer 1

2 to 5 years

Question 2

when is myelination of peripheral nerve fibers complete?

Answer 2

age 5 years

Question 3

motor conduction velocities - when do they reach adult values?

Answer 3

ages 3-5 years

Question 4

when do CMAP amplitudes reach adult values

Answer 4

end of first decade of life

Question 5

what happens to f-waves in children?

Answer 5

no changes in f-wave latency as the arm length and conduction velocity are increasing a lot from age 0 to 3 years, but after age 3, arm length continues to increase and the F wave latency increases commensurately now that myelination is more stable

Question 6

h-reflexes in kids

Answer 6

you can get lots of H reflexes in many nerves up to age 1 because of the lack of myelination, then it is difficult to obtain. In adults, you can usually only get tibial to soleus and radial nerve to FCR

Question 7

in newborns, what is considered abnormal repetitive nerve stimulation?

Answer 7

decrement of 10% or more between initial and fourth or fifth responses at 2 Hz, or an increment of greater than 23% at 20-50 Hz

Question 8

EMG MUAP durations in infants

Answer 8

1-4msec (in adults, it’s 3-15msec)

Question 9

electrodiagnostics findings in CMT

Answer 9

depends if demyelinating or axonal form.
demyelinating form has MNCV <38 and axonal form has MNCV >38 in median nerve

CMT1 - needle EMG shows defibrillation with sharps, large polyphasic MUAPs.

CMT2 - chronic denervation and reinervations

Question 10

type 1 diabetes and electrodiagnostic findings

Answer 10

impaired motor distal latency and SNAP amplitude

Question 11

infantile botulism electrodiagnostic findings?

Answer 11

normal motor and sensory nerve conductions. RNS abnormal
needle EMG with small MUAPs and sometimes sharps and fibs