Abstract Details

Title F/M Wave Area And F-Wave Duration Quantify Spinal Hyperexcitability in Glutamic Acid Decarboxylase (GAD) Antibody Positive Patients with Stiff Person Syndrome.

Topic Autoimmune Neurology

Presentation(s) P2 - Poster Session 2 (5:30 PM-6:30 PM)

Poster/Presentation
Number 15-031

Objective To explore the late compound muscle action potential (F) wave in GAD antibody positive patients as potential measure of spinal cord excitability and diagnostic indicator in stiff person syndrome (SPS).

Background SPS is an autoimmune disorder characterized by progressive muscle stiffness, spinal deformity, and trigger induced muscle spasms. Loss of inhibitory neurotransmission in the spinal cord due to antibodies is thought to be the pathophysiological mechanism. About 80% of SPS patients have GAD antibodies. F-wave generation on electrophysiology is known to reflect the excitability of spinal motor neurons

Design/Methods Five anti-GAD positive SPS patients, mean age 59 years (3 male, 2 female), and 6 healthy controls (HC), mean age 52 years (2 male, 4 female), were included. We measured the F/M wave area and amplitude ratio along with F-wave duration and persistence from peroneal (n=43) and tibial (n=69) nerves of SPS patients and compared healthy controls (peroneal n=52 and tibial n=81) using independent t-test.

Results The average F/M area ratio of peroneal (SPS: 0.05 ± 0.08, HC: 0.02 ± 0.01, p-value=0.01) and tibial (SPS: 0.11 ± 0.23, HC: 0.05 ± 0.03, p-value=0.03) nerves was significantly higher in SPS. Average F/M amplitude ratios were not significantly different. Average duration was 71 millisecond (ms) (SPS) and 8 ms (control) for peroneal and 61 ms (SPS), 17 ms (control) for tibial.

Conclusions We found the F/M wave area ratio and the F-wave duration was higher in the SPS patients compared to HC, consistent with increased spinal motor neuron excitability in SPS patients. The long duration of the F-response indicates greater dispersion, which alone would not necessarily imply greater excitability, but helps to explain the superiority of the area ratio to the amplitude ratio as a measure of excitability. We propose that F/M wave area and duration may serve as a consistent diagnostic marker in SPS.

Authors/Disclosures
Mahmood Shbeb, MD (Cleveland Clinic) PRESENTER	Dr. Shbeb has nothing to disclose.
Shitiz K. Sriwastava, MBBS (UT Health Houston)	Dr. Sriwastava has nothing to disclose.
Kalyan Yarraguntla, MD (University Health Center)	Dr. Yarraguntla has nothing to disclose.
Abbas Jowkar, MD (Henry Ford Health System)	No disclosure on file
Edwin B. George, MD, PhD, FAAN (Food and Drug Administration)	No disclosure on file

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