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Sequential NCV Tests: Correlate with Symptoms

Guillain-Barre at Onset and Nadir

History: Strohl and Myographic Curves

In 1859 Landry described an ‘ascending paralysis’ in 10 patients, but the location of the illness remained undiscovered:

Three of the patients perished, but even at autopsy the peripheral nerves were not examined or considered.

The next contribution was the classic 1916 paper from French doctors Guillain, Barré, and Strohl which reported a neuropathy in two French soldiers.

This is the first record of our now-standard diagnostic tests for Guillain-Barre. The cerebrospinal fluid when examined showed elevated protein without cellular reaction.

In addition, Strohl performed electro-physiological tests on the two soldiers, which they called ‘myographic curves.’

Sequential NCV Tests Three Weeks Apart

When I contracted Guillain-Barre Syndrome, my neurologist performed the tests which the pioneering French doctors – Guillain, Barré, and Strohl – set as the gold-standard in their classic paper of 1916. These test are cerebrospinal fluid evaluation, and electrodiagnostic evaluation in the form of Nerve Conduction Velocity (NCV) tests.

In my case, for comparison purposes, two Nerve Conduction Velocity studies were done spaced three weeks apart. The NCV exams, respectively, were ten days and four weeks after the onset of Guillain-Barre symptoms. The full NCV results (graphs, tables and diagnostic reports) appear at:

Guillain-Barre Onset

History – This disease earned many agnomens (honorary names). The most descriptive was Landry's Ascending Paralysis, apt because the symptoms of paresthesia and weakness typically arise first in the extremities: the feet and fingertips. The reason is statistical: The longest nerves offer more locations for attack by anti-ganglioside antibodies. Symptoms travel rapidly upward in the legs and arms, then into the body core: this reflects antibody hits on shorter and shorter nerves, of sufficient quantity to affect conduction.

My Case of Guillain-Barre – Sensory symptoms appeared first (numbness and tingling; a pins-and-needles feeling), followed in a few days by muscle weakness brought on and exacerbated by exercise. Autonomic symptoms arose early and were severe, charted during my three visits to the ER of St. Paul's Hospital. There, a young Resident also established with meticulous measurements that my lower-limb reflexes were entirely absent, kaput.

The brief timeline below lists the events at onset. For a more inclusive list of symptoms, go to my contemporaneous personal account published in The Medical Post. Additional Chart Notes cover two topics in depth: (1) my specific autonomic symptoms and response to treatment; and (2) the monophasic profile of the motor weakness and patient adaptive methods.

Guillain-Barre Onset of Symptoms
  • Mid-Sept First sensory symptoms (slight, temporary)
  • Sept 19 Sensory symptoms return (intense); pain in upper backGBS Onset
  • Sept 20 Exercise (aerobics and light weights)
  • Sept 21 Previous day's exercise set me back, not forward: can now walk
    only in slow-motion; the sensory symptoms extend
  • Sept 22-27 Seek care: Visit GP, plus 3 visits to Hospital ER where chart reports
    autonomic symptoms (BP, pulse); lower limb reflexes are absent
  • Sept 27 Finally admitted to hospital
  • Sept 28 Spinal tap: elevated protein, no white-cells
  • Sept 29 First Nerve Conduction Velocity test NCV 1
  • Oct 11 Spinal tap: elevated protein, no white-cells (as before)
  • Oct 18 Second Nerve Conduction Velocity testNCV 2

Guillain-Barre Nadir

Ideally an NCV test should capture Guillain-Barre at the nadir – the point of maximum damage to the peripheral nerves, before regeneration begins to the myelin and axons. My second NCV test was performed four weeks from disease onset, which coincides with the nadir that I experienced.

Thus we may correlate the results of this second NCV test with my account from The Medical Post which elucidates my symptoms at the point where muscle weakness reached maximum:

I spiral downward. Four weeks from onset I reach the nadir. Paresthesia (numbness and tingling) extends from toes to crown. Swallowing is stiff. My bowels block. Gravity defeats everything. I can no longer grip a pen or hold up a newspaper, nor am I self-mobile in a wheelchair.

Guillain-Barre attacks striated or voluntary muscle, leaving alone smooth muscles such as the heart and diaphragm. My diaphragm, highly developed from the bagpipes, may be what saves me from a respirator, for by now my chest muscles are shudderingly weak.

Compare Nerve Conduction Velocity Tests

A technical comparison between sequential NCV tests, for the same patient, illustrates the rapid evolution of peripheral nerve damage in Guillain-Barre Syndrome. In my first NCV test, 10 days after symptom onset, the compound muscle action potential (CMAP) already has low amplitude, which correlates with axonal degeneration. It also correlates with an ominous prognosis.

My second NCV test, at 4 weeks, shows these additional features: Temporal dispersion of the CMAP, which gives the graphs a ragged appearance – different from the smooth fast sine-wave of normal muscle. Conduction slowing is now evident, delaying the CMAP on the time axis. There is prolonged distal latency, also diagnostic of GBS.

My NCV tests were performed by neurologist Dr. Peter Siemens at the Clinical Neurophysiology Laboratory of Royal University Hospital, Saskatoon, Canada. The tables below contain extracts from the diagnostic reports:

NCV Test #1 — Ten Days from GBS Onset
Motor Nerves Distal latencies prolonged in all motor nerves (median, ulnar, tibial, peroneal). There is a first glimmer of slowed conduction velocity.
Sensory Nerves Distal latencies of sensory nerves (median and ulnar) are still normal, but the amplitude of the response is very low.
F Waves F Wave latencies of median and peroneal nerves show conduction block.
Diagnosis Report:  The findings would be consistent with a polyneuropathy.
NCV Test #2 – Four Weeks from GBS Onset
Motor Nerves Further slowing of conduction velocity is plainly evident.
Distal latencies markedly prolonged, much more than in previous exam.
Temporal dispersion of compound muscle action potential (CMAP).
Sensory Nerves Complete conduction block in median and ulnar sensory nerves.
F Waves The F Wave latencies of all nerves now show conduction block.
Diagnosis Report:  The findings are indicative of an acute polyneuropathy.
Georgena S. Sil
Saskatoon, Canada
Physicist & Technical Writer
Alumnus: University of British Columbia
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Distal Latency

Distal latency measures the integrity of the junction between nerve and muscle (the neuromuscular junction).

A peripheral nerve exits the spinal cord, runs a distance, them embeds in its target: a bundle of closely-spaced muscle fibers (one bundle has 10 to thousands of fibers).

In the NCV test, the electrode on the skin replaces a signal from the brain. The body functions identically, however.

When the electrical impulse reaches the nerve tip, it stimulates the release of acetylcholine (ACH) into the junction space (a small cleft), and this makes the muscle fibers contract.

The time it takes for the ACH to travel across the junction space and trigger a muscle contraction is called distal latency.

Distal latency is abnormally long in GBS.

Distal = end / Latency = time

Resource:  GBS Overview (Steinberg)


Proximal Latency

In an F Wave study, an electrode on the skin stimulates a motor nerve, but the signal travels upward to the spinal column, to the nerve's anterior horn cell, or nerve root.

The F Wave signal then reflects or ricochets back to the electrode which sent the pulse.

The time for the round-trip is called F Wave latency. The electrode is placed precisely, its location carefully measured, to yield the distance the signal must travel.

This data (latency and distance) is then used to calculate the conduction velocity in proximal segments of motor nerves.

In Guillain-Barre Syndrome, F Wave latency is often prolonged or unobtainable. This signifies demyelination or conduction block in proximal segments.

Proximal = close to the center
(the opposite of distal)

Unobtainable = zero amplitude
(signal is absent)

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