Diagnostics Flashcards
How do myopathic potentials look on an EMG
Increased frequency (greater than 4 phases), decreased amplitude and duration - results from increased number of action potentials required for a given contraction
How do neuropathic potentials look on an EMG
Decreased frequency and longer duration - might occur during minimal and maximal contraction. Thus - see fewer MUAPs of increased amplitude than expected for the strength of contraction
Causes of neuropathic potentials?
Primary neuropathies where collateral reinnervation has occurred
Causes of myopathic potentials?
Polyphasic - occur in myotonia like syndromes e.g. periodic paralysis, myotonia, botulism, myaesthenia gravis like syndromes - occasionally PPID
What are fibrillation potentials
Spontaneous discharges - have initial positive deflection (100-300uv in amplitude) and are diphasic or triphasic - suggest denervation
Have also been observed in polymyositis, botulism and muscular dystrophy
How long do fibrillation potentials take to occur after denervation?
7-10 days in horses - often with positive sharp waves
What are positive sharp waves
Potentials where primary deflection is downward, followed by a lower amplitude longer duration positive deflection - resembles a saw tooth
Occur with denervation and muscular diseases e.g. myositis, ER and spinal shock
May occur after EPM, myotonia, chronic ER, sweeney and compressive myelopathies
What are fasciculation potentials
Spontaneous discharges from a group of fibres representing whole or part of a motor unit - occur in diseases of anterior horn cells or irritative type lesions of the root or peripheral nerve
What are complex repetitive discharges and myotonic potentials?
Repetitive MUAPs induced by insertion of needle electrode or percussion of muscle
Myotonic - wax and wane and sound like a dive bomber - associated with membrane hyperexcitability
