3 Motor Pathways Possible places of dysfunction CNSEEG ElectroencephalographyPET Positron Emission TomographyfMRI Functional Magnetic Resonance Imaging
4 Motor Pathways Possible places of dysfunction 2. MuscleNeedle EMG ElectromyographyCNSEEG ElectroencephalographyPET Positron Emission TomographyfMRI Functional Magnetic Resonance Imaging
5 Motor Pathways Possible places of dysfunction 2. MuscleNeedle EMG ElectromyographyCNSEEG ElectroencephalographyPET Positron Emission TomographyfMRI Functional Magnetic Resonance Imaging3. Peripheral NerveNerve conduction study
6 Peripheral Nerve MEDIAN ULNAR Made up of: Sensory nerves Motor nerves MyelinGlial cellsMEDIANULNAR
7 Median Nerve Pathology in Carpal Tunnel Syndrome Compression of the median nerve results inDemyelinationAxonal degenerationDecreased blood supplyThese manifest as:- Numbness- Pain- Parasthesiae- Weakness- Problems with fine manipulative skills
8 Nerve Conduction Study Stimulate nerve and record outcome.2 main types1. Motor (record compound muscle action potential)2. Sensory (record compound sensory action potential)-Orthodromic (stimulate at finger, record on elbow/wrist)-Antidromic (stimulate at elbow/wrist, record on finger)-Radial-median (stimulate at wrist, record on thumb)-Palmar (stimulate at palm, record on elbow/wrist)Most sensitiveLeast sensitive
9 Changes to CMAP in Carpal Tunnel Syndrome Latency: Normal < 4.9 msAmplitude: Normal ≥ 5 mVShape: Normal curvePathology: - demyelination- axonal degenerationTimeResponse amplitude
10 Nerve Conduction Study Measures Latency and AmplitudeLatency is the time between the artefact and the initiation of the compound action potentialThe artefact occurs when you press the button to stimulate the electrodeLatency increases pathologically due to:Axonal degenerationDemyelinationLatency increases non-pathologically due to:Length of axon
11 Nerve Conduction Study Measures Latency and AmplitudeThe amplitude of the curve shows the strength of the compound action potentialThe area under the curve decreases pathologically due to:Number of axons involvedDiameter of nerveThe area under the curve decreases non-pathologically due to:Strength of initial stimulus
12 Nerve Conduction Study Motor Nerve Conduction Study Setup:Stimulating electrode to set up action potentials in median nerve from wrist or elbowRecording electrode on abductor pollicus brevis to record compound muscle action potentialTechniques to increase effectiveness of stimulationEarth
13 Conduction VelocityImportance: Eliminating wrong localisation of problemMethod:1swrLatency wrist2serLatency elbow
15 Conduction Velocity Normal value > 50 m/s Other sources of error – stimulus position- estimation of nerve course- latency measurement
16 Problems with comparing features to normal values Features change withTemperatureAgeAge2080LatencyAgeCV• Solution: Repeat measurements on ulnar nerve as a control. This also gives additional evidence to rule out generalised neuropathy.
17 Compound Antidromic Sensory Action Potential Setup:- stimulate at wrist/elbow and record at finger- gain set higher- signal very small so average random noise• Normal values:- Latency < 3.6 ms- Velocity > 50 m/s- Amplitude > 15 mV- Latency < 3.1 ms- Velocity > 54 m/s- Amplitude > 10 mVMEDIAN SENSORY (ANTIDROMIC)ULNAR SENSORY (ANTIDROMIC)
18 An example: Right Antidromic Ulnar Normal:-Lat < 3.1 ms-Amp > 10 uV…. Ulnar OK – not generalised neuropathy
19 An example: Right Antidromic Median Normal:-Lat <3.6 ms-Amp >15 uV-CV >50 m/s…. In median nerve, evidence of demyelination and axonal degeneration between wrist and finger, but not between wrist and elbow. Suggestive of carpal tunnel syndrome.
20 An example: Right Thenar Median Normal:- Lat < 4.9 ms- Amp ≥ 5 mV- CV > 50 m/s…. Motor portion of median is OK. Mild to moderate carpal tunnel syndrome.
21 Take home message!In carpal tunnel syndrome there will be a longer latency between the wrist and the finger/thenar eminence but NOT between the elbow and the wristThe ulnar nerve will not be effected in carpal tunnel syndrome because it does not pass through the carpal tunnel