Neurodiagnostic Testing

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Neurodiagnostic Testing

• Amir Arain M.D.
• Department of Neurology
• Vanderbilt University Medical Ctr.

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Neurodiagnostic Testing

• Neurologists like to localize and characterize
  the disease.
• Treatment is based on the findings
• Neurological exam provide strong clues
• Neurological exam has some limitations
• Neurodiagnostic tests help to overcome these
  limitations

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Neurodiagnostic Testing

• The Neurodiagnostic testing helps
• in assessing the disease
• in monitoring changes in neural function
• to monitor the neurologic status
• to define the prognosis
• to quantitate the severity with reproducible
  measures

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Neurodiagnostic Tests

• EEG
• Evoked potentials
• EMG
• Polysomnography and MSLT
• Autonomic testing

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EEG

• Electroencephalography
• records the electrical activity of the brain
• it measures the functioning of the neurons
• it reflects the synchronized postsynaptic
  potentials of the dendrites of the cortical
  neurons.

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EEG

• Postsynaptic potential can be EPSP and IPSP
• EEG is helpful in evaluation of
• seizures
• transient ischemic attacks
• syncopal attacks
• psychogenic attacks

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EEG

• There are four basic frequencies
• Alpha occipital predominant
• Beta frontally predominant
• Theta normal in awake young children
• Delta normal in infants

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EEG

• Most frequently used to detect seizures
• mostly interictal discharges are seen
• the diagnostic yield depends on the number of
  sampling. By four EEGs the maximum yield gt94 is
  achieved
• some people may always have normal EEG despite
  having epilepsy

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EEG

• Interictal EEG patterns
• focal spikes and sharp waves
• gt90 of epileptic adults have partial epilepsy
  and 90 of them have temporal lobe epilepsy
• generalized spike and wave discharges
• more common in children

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EEG

• Generalized epilepsy can be with
• absence seizures
• GTC seizures
• atypical absence seizures
• myoclonic seizures
• atonic seizures
• tonic seizures

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EEG

• EEG is helpful in assessing the level of
  consciousness. It can show
• triphasic waves
• periodic discharges (generalized) or focal
  (PLEDS)
• Burst suppression pattern
• coma patterns and brain death

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EEG

• Types of EEG
• routine
• ambulatory EEG
• video EEG
• prolonged video EEG monitoring with drug
  withdrawal
• intra-operative monitoring (ECoG)

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Evoked Potentials

• The responses of nervous tissue to stimulation.
• Motor or sensory evoked responses
• sensory evoked potentials
• VER
• BAER
• SSER

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VER

• Provides a qualitative and sensitive evaluation
  of the visual pathway
• monocular stimulation produces a positive wave
  (P100) with a mean a latency of 100 msec.
• P100 is very sensitive to the disease affecting
  optic nerve and anterior chiasm.

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VER

• Demyelinating processes prolong the latency of
  P100
• compressive lesions decrease the amplitude of the
  P100 response.
• Once abnormal the VER tends to remain abnormal.
• It may be abnormal in person with normal exam

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BAER

• A square wave click stimulus is delivered to one
  ear at a time and response recorded.
• 7 waves are recored.
• Wave 1 originates from distal 8th nerve
• wave 3 ipsilateral lower pons
• wave 5 ipsilateral midbrain

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BAER

• Absolute and interpeak latencies are noted.
• Disease prolong the interpeak latencies
• a reduction in auditory acuity may result in
  absence of wave 1 with a delay in the other
  waveform abnormalities

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BAER

• BAER is abnormal in
• CP angle tumor
• Brainstem tumor/infarction
• Demyelinating disorders
• Leukodystrophies
• They are most helpful in acoustic neuromas and
  multiple sclerosis

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SSER

• SSER are obtained in upper extremities with
  stimulation of median or ulnar nerve. Recording
  at Erbs point, neck and scalp
• SSER in lower extremities are obtained with
  stimulation of posterior tibial or Peroneal
  nerves. Recording at lumbar region and scalp

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SSER

• SSER are carried by dorsal column.
• Absolute latencies and interpeak latencies are
  evaluated.
• SSER can detect clinically silent lesions in
  multiple sclerosis or demyelinating
  disorders.SSER can distinguish between a central
  and peripheral process

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SSER

• SSER are used in evaluation of comatose patients.
• Scalp SSER are lost in brain dead patients
• SSER are used to monitor patients undergoing
  spine or spinal cord surgery.

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EMG

• Electromyography studies the sensory nerves and
  the motor unit
• motor unit
• root
• plexus nerve axons, peripheral n axon
• plexus nerve myelin, peripheral n myelin
• neuromuscular junction
• muscle

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EMG

• Two parts
• NCS (nerve conduction studies) to check the
  functioning of the nerves directly
• Needle EMG to check for the functions of the
  muscle directly and the nerves indirectly.

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Nerve Conduction Studies

• Time required for the nerve conduction is
  measured by stimulation of a peripheral
  recording potentials from nerve or muscles
• Myelinopathy slow the conduction velocity. If
  severe conduction block
• Axonopathy decrease the amplitude

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NCS

• NCS is helpful in compressive neuropathies
• types of NCS
• F wave H reflux
• Blink study
• sympathetic skin response
• Repetitive stimulation

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Case

• A 35 year old female reports of blurred and
  double vision at night
• her speech becomes slurred at night
• She feels tired at the end of the day
• She feels fresh and energetic in the morning

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Case

• A 35 year old woman has weakness and difficulty
  walking up the stairs
• She can not open glass jars
• She has difficulty getting out of chair
• No sensory problem

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Electromyography

• The recording of motor unit potentials
• can distinguish b/w neuropathic and myopathic
  processes
• Neuropathic fibrillation, positive sharp waves,
  polyphasic motor units
• Myopathic MUPs of reduced amplitude
• polyphasic with a normal duration

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Abnormal EMG activity
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Sleep Study

• Polysomnography recording of multiple
  physiologic parameters of sleep.
• To asses daytime sleepiness
• to asses sleep disordered breathing
• narcolepsy and idiopathic hypersomnia
• periodic limb movements of sleep
• to evaluate parasomnias and insomnia

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Normal sleep architecture

• Non REM sleep 75 of an adult sleep
• REM (Rapid eye movement sleep) 20-25of adult
  sleep
• NREM Stage1
• Stage2
• Stage3
• Stage4

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Stages of Sleep

• Stage 1 disappearance of alpha rhythm
• Stage 2 appearance of spindle / K- complexes
• Stage 3 EEG with delta activity 20-50
• Stage 4 EEG with delta activity gt 50

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Awake
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Stage 1
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Stage 2
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Stage 4
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REM rapid eye movement sleep
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Sleep disorders

• Narcolepsy MSLT (multiple sleep latency test)
• Obstructive sleep apnea most common cause of
  excessive daytime sleepiness
• periodic leg movements of sleep
• REM behavior disorder
• Parasomnias

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Autonomic testing

• Generalized autonomic failure MSA
• Benign autonomic disorders syncope
• Painful distal small fiber neuropathy or
  neuropathy with significant autonomic involvement
• Orthostatic intolerance
• Reflux sympathetic dystrophy

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Autonomic Testing

• Sympathetic skin response
• Heart rate response to deep breathing(cardiovagal
  parasympathetic, cholinergic fibers)
• Valsalva maneuver (cardiovagal and adrenergic
  function)
• BP and pulse response to upright tilt