Afferent inhibition and cortical silent periods in shoulder primary motor cortex and effect of a suprascapular nerve block in people experiencing chronic shoulder pain

Lynley Bradnam; E Michael Shanahan; Kirsty Hendy; Amalia Reed; Tegan Skipworth; Anri Visser; Sheila Lennon

doi:10.1016/j.clinph.2015.03.012

Afferent inhibition and cortical silent periods in shoulder primary motor cortex and effect of a suprascapular nerve block in people experiencing chronic shoulder pain

Clin Neurophysiol. 2016 Jan;127(1):769-778. doi: 10.1016/j.clinph.2015.03.012. Epub 2015 Apr 4.

Authors

Lynley Bradnam¹, E Michael Shanahan², Kirsty Hendy³, Amalia Reed³, Tegan Skipworth³, Anri Visser³, Sheila Lennon³

Affiliations

¹ Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia; Applied Brain Research Laboratory, Centre for Neuroscience, School of Medicine, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia. Electronic address: lynley.bradnam@flinders.edu.au.
² Department of Rheumatology, Repatriation General Hospital, Adelaide, South Australia, Australia; School of Medicine, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.
³ Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.

PMID: 25900020
DOI: 10.1016/j.clinph.2015.03.012

Abstract

Objective: To characterise short afferent inhibition (SAI) and the cortical silent period (CSP) in the primary motor cortex representations of the infraspinatus muscle in healthy adults and people experiencing chronic shoulder pain, to determine the impact of a suprascapular nerve block (SSNB).

Methods: Neurophysiological measures were obtained in 18 controls and 8 patients with chronic shoulder pain, pre and post SSNB and 1 week later. Pain intensity was assessed by a visual analogue scale.

Results: SAI was apparent in controls (all P<0.03) and a CSP was observed which reduced in the presence of SAI (all P<0.0001). Compared to controls, shoulder pain patients demonstrated higher active motor threshold (P=0.046), less SAI (P=0.044), a longer CSP (P=0.048) and less modulation of the CSP by SAI (P=0.045). Higher motor thresholds were related to higher pain scores (P=0.009). The SSNB immediately restored SAI (P=0.013), with a positive relationship between increased SAI and reduced pain (P=0.031). The SSNB further reduced modulation of CSP by SAI at 1 week post injection (P=0.006).

Conclusions: SAI and the CSP were present and demonstrated robust interaction in controls, which was aberrant in patients. The SSNB transiently restored SAI but had no effect on the CSP; however CSP modulation by SAI was further attenuated 1 week post injection.

Significance: The current findings improve understanding of the neurophysiology of the shoulder motor cortex and its modulation by chronic pain. The effect of SSNB in shoulder pain patients should be interpreted with caution until proven in a larger population. Interventions that target intracortical inhibition might increase efficacy in people with chronic shoulder pain.

Keywords: Chronic shoulder pain; Cortical silent period; Infraspinatus; Short afferent inhibition; Suprascapular nerve block; Transcranial magnetic stimulation.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adult
Afferent Pathways / physiology
Aged
Chronic Pain / diagnosis
Chronic Pain / physiopathology
Chronic Pain / therapy*
Cohort Studies
Electromyography / methods
Female
Humans
Male
Middle Aged
Motor Cortex / physiology*
Nerve Block / methods*
Neural Inhibition / physiology*
Pain Measurement / methods
Scapula / innervation
Scapula / physiology
Shoulder Pain / diagnosis
Shoulder Pain / physiopathology
Shoulder Pain / therapy*
Transcranial Magnetic Stimulation / methods*
Treatment Outcome
Young Adult