IDENTIFICATION OF SURAL NOCICEPTIVE FLEXION REFLEX RATIO IN ADULT MALES 20-40 YEARS OF AGE

Thien Ngo MDPGY – 4UK PM&R 5/23/2013Advisors: Drs. Lumy Sawaki & Oscar Ortiz

Outline

Introduction Objectives Experimental Design Method Results References

Introduction 1

Pain is a subjective experience, and its measurement has been traditionally based on self reported instruments.

Absence of objective instruments Quantitative sensory testing and

nociceptive flexion reflex (NFR) threshold have been explored as options to measure pain more objectively

Introduction 2

NFR in theory The NFR is a polysynaptic spinal

reflex subserving withdrawal from potentially noxious stimuli.

Provide indirect evidence of supraspinal modulation The higher the threshold the more

inhibition of spinal nociceptive transmission

Introduction 3 NFR threshold is defined by the lowest

noxious stimulation intensity required to trigger a reflex motor response in the biceps femoris muscle.

Introduction 4

Central hyperexcitability as measured with nociceptive flexor reflex threshold in chronic musculoskeletal pain: a systematic review.

Lim EC, Sterling M, Stone A, Vicenzino B.Pain. 2011 Aug;152(8):1811-20. Epub 2011 Apr 27

Introduction 5

Promising results in multiples experimental studies. Reliable, reproducible, and correlated

well with clinical findings within subjects

Significant variability between subjects, despite efforts for standardization, makes it unsuitable for clinical use or establishment of normal values.

Propose alternative standardized method to measure NFR that avoid variability (mostly due to changes in skin resistance).

Introduction 6

NFRI =Sural SNAP amplitude using NFRT stimulus

Sural SNAP amplitude (supramaximal)x 100

Objectives

The goal of this pilot study is to begin to establish normative data of NFRI in young male adults. Our proposed study has 2 specific aims:

Specific Aim #1:Identify the “normal” sural nociceptive flexion reflex threshold (NRFT) and the sural nociceptive flexion reflex ratio (NFRR) in male adults of 20 to 40 years of age.

Specific Aim #2:Measure the correlation between the NFRI and level of pain as measured by Visual Analogue Scale (VAS).

Experimental Design

Recruitment: Flyers and volunteer subjects Screening process and informed consent Inclusion Criteria:

Healthy male 20-40 Exclusion Criteria:

Avoiding confounding factors of NFR and NFRT recording Head injury, alcohol/drug abuse, psychiatric

illness, on psychiatric/pain medications, neurological disorder, chronic pain, h/o cancer, and peripheral neuropathy

Method (Step 1) (Sural sensory nerve action potential)

EMG Machine

Method (Step 2) (Nociceptive Flexion Reflex)

EMG machine - Biceps Femoris Reflex

Graph 1: Subject by Subject Responses: biceps reflex, pain index, and NFRR

Graph 1. Pain index and NFRR showed a closed correlation with subject 1, 2, 4, 6, & 7. There was no significant correlation between pain and biceps reflex intensity.

Graph 2: Correlation between pain index vs biceps reflex

Graph 2. Biceps Reflex (mA) vs Pain Index showed 59% correlation

Graph 3: Pain index vs NFRR

Graph 3. Lack of a correlation between pain index and NFRR

Conclusion/Discussion:

No significant findings Variability

Take away points Revise gold standard

Minimal threshold for SNAP Standard stimulus for pain index

References

1.) Giorgio, S. et al. “The lower limb flexion reflex in humans”. (2005) Progress in Neurobiology 77: 353-395.

  2.) Rhudy, J. & France, C. “Defining the nociceptive flexion reflex (NFR)

threshold in human participants: A comparison of different scoring criteria”. (2007) Pain 128: 244-253.

  3.) France, C. et al. “Using normalized EMG to define the nociceptive flexion

reflex (NFR) threshold: Further evaluation of standardized NFR scoring criteria”. (2009) Pain 145: 211-218.

  4.) Terry, E. et al. “Standardizing procedures to study sensitization of

human spinal nociceptiveprocesses: Comparing parameters for temporal summation of the nociceptive flexionreflex (TS-NFR)”. (2011) International Journal of Psychophysiology 81: 263-274.

  5.) Micalos, P. et al. “Reliability of the nociceptive flexor reflex (RIII)

threshold and association with Pain threshold”. (2009) Eur J Appl Physio 105: 55-62.

Thank you!