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Normal & Abnormal Nerve Conduction Study (NCS) Findings

 Below are a few examples of common EMG/NCV abnormalities in several peripheral nerve disorders.

Carpal Tunnel Syndrome (CTS) is the most common peripheral entrapment neuropathy.  Only the median nerve travels through the tunnel, and thus only the median motor & sensory latencies are delayed across the wrist.  Below, NCS reveals not only significant delay of all median latencies relative to predicted, but also by differential median compared to ulnar and radial latency comparisons, particularly so for the median midpalm sensory latency (a short distance latency across the carpal tunnel), compared to the ulnar midpalm sensory latency. There is also median vs. ulnar motor latency delay.  The more the delay, particularly when lost amplitude and waveform dispersion, the more significant is the compression.  Additionally, EMG details mild active denervation in the median innervated muscle, as well as chronic motor unit reorganization, and thus a total picture for a moderately-severe form of CTS. 

 

Electrodiagnostic Pattern of CTS
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Ulnar neuropathy at the elbow is probably the second most common entrapment neuropathy.  Below, NCS reveals absence of the ulnar sensory responses above the elbow, and significant ulnar slowing with a near complete neurapraxic conduction block at the level of the elbow defined by inching technique to be located precisely behind the tip of the medial epicondyle.  EMG shows denervation in the ulnar distribution as well as motor unit reorganization with rapid firing reflecting axonal/nerve fiber injury and loss. 

Ulnar Neuropathy of the Elbow
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True Tarsal Tunnel Syndrome (TTS) which is an unusual distal posterior tibial entrapment neuropathy of the ankle and foot, the analog to CTS of the wrist and hand, should not be overlooked as it is treatable.  This must be differentiated from musculoligamentous problems such as plantar fasciitis vs. isolated branch plantar neuropathy vs. generalized distal lower extremity peripheral neuropathy (“sick” nerve neuropathy). 

Below left, left sided medial and lateral plantar sensory responses are easily defined, but right sided responses are absent.  Below right, left sided medial and lateral plantar motor latencies across the ankle/tarsal tunnel are normal, but right sided plantar latencies across the ankle are prolonged with the amplitude of responses diminished (reflecting axonal/nerve fiber loss). The normal left sided motor and sensory responses and bilateral motor conductions rules out a generalized peripheral neuropathy.


True R TTS Prolonged
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Generalized lower extremity peripheral neuropathy in distinction to Tarsal Tunnel Syndrome.  There is diffuse and not focal motor and sensory abnormalities. 

Below left, the bilateral medial and lateral plantar sensory responses are symmetrically prolonged and of tiny amplitude nearing unobtainable.  Below right, the bilateral medial and lateral plantar motor latencies are prolonged and of tiny amplitude with significant but symmetric motor conduction slowing defined ankle to knee.


GPN not TTS Bilaterally
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