neurophysiology Flashcards
what is Neurophysiology useful for in MND diagnosis
exclude mimics:
multi focal motor neuropathy with conduction block,
radiculopathy,
CIDP,
myopathy,
myasthenia gravis.
Uncover subclinical MND loss which can mean an earlier diagnosis
what can be done if diagnostic uncertainty persists
repeat examinations
what areas are typically examined with Neurophysiology for MND
1)ARM:
NCS, EMG
2) leg: NCS, EMG
3) thoaracic paraspinals EMG
Tongue/cranial muscles -EMG
what should you find with a sensory nerve conduction study in MND
normal function and action potentials as MND is by definition solely motor system affected
what NCS effects will be measured in MND
early disease: CMPAPs:
normal MCV:
LATE disease: CMAPs Small, MCV: minimal effect
explain the phenomenon of maintained conduction speed and redcued CMAPs in MND
conduction speed dependant on myelin, therefore not a feature of MND,
some slowing may be present if biggest MNs with fastest axond lost.
CMAP: as motor neuron dies, axon dies too, early disease ohase sprouting of remaining neurons compensates, in later phases, re-innervation fails. CMAP smaller
what are the EMG features of MND
a normal relaxed muscle should record nothing.
Hallmark of MND:
floroid denervation,
devervated fibres spontaneously fire,
as muscle fibres fire- fibrillation potentials and positive sharp waves,
fasiculation potentials
are fasiculation potentials specific or non-specific to MND?
Non specific as seen in bening cramp fasiculation syndrome and in normal health indivduals
what does the recorded EMG signal refelect?
density of muscle fibres, how close they are to needle
what does EMG look for evidence of?
denervation and re-innervation
Denervation: fibrillation potentials, positive sharp waves, fasiculation potentials.
Reinnervation: MUAPs: long duration MUAPs, high amplitude MUAPS
what are the four areas and coropsonding criteria defined by both ALS criteria?
1) Cranial/bulbar region: EMG: one abnormal muscle required
2) cervical region EMG: 2 abnormal muscles required, innervated by different nerves & roots
3) thoracic region EMG-one abnormal muscle required
4) lumbar region: 2 abnormal muscles required, innervated by different nerves and roots.
what are some criticisms of el escorial criteria?
EMG not given equal waiting with physical examination,
may take longer to reach diagnosis, fasiculations not counted
what is a benefit of the awaji shima criteria?
EMG findings given equal significant to LMN findings on clinical examination,
fasiculation potentials allowed.
Increases diagnoistic sensitivity from around 30% to 60% without comprimising specificity (douglas et al 2010)
how can UMN dysfunction be measured ?
TMS to stimulate motor cortex,
then record a response from limb muscle : the motor evoked potential
