Investigating the sensitivity of the central nervous system in patients with chronic low back pain radiating to the leg

There is growing evidence for sensitisation in patients with chronic pain. Continuing nociceptive inputs can induce a reduction in threshold and an increase in responsiveness of peripheral nociceptors, i.e. peripheral sensitisation, which on itself may lead to a prolonged increase in excitability and synaptic efficacy of neurons in central nociceptive pathways, i.e. central sensitisation. Several methods are advocated to measure central sensitisation. For example, quantitative sensory testing (QST) is a psychophysical method that objectively measures responses to calibrated graded innocuous or noxious stimuli and represents, in most respects, an extension of the routine standardised sensory measurements. Furthermore, central sensitisation can be assessed with the Central Sensitisation Inventory (CSI). For treatment of severe cases of chronic low back pain, patients are referred to multidisciplinary pain clinics for further assessment. If the diagnosis in patients with chronic low back pain radiating to the leg (CLBPr) is not clear despite extensive physical, neurological, orthopaedic and radiological examination, a precision diagnosis, such as diagnostic segmental nerve root block (dSNRB), has been advocated. After a positive dSNRB, possible interventions are therapeutic SNRB (tSNRB) or pulsed radiofrequency (pRF). The extent of central sensitisation in patients with CLBPr, its role in chronification and its interaction with diagnostic and therapeutical interventions are unknown up to now.

Therefore, the main questions of this study are: can we find signs of central sensitisation in patients with CLBPr? Can we quantify it? Do the interventions (tSNRB and pRF) normally applied in care as usual affect central sensitisation?

To determine the presence or absence of central sensitisation in patients with Chronic Low Back Pain with radiation to the leg (CLBPr) and to determine the effect of segmental nerve interventions on central sensitisation.

T1=measurements before diagnostic SNRB

T1a = optional measure 1 week after first diagnostic SNRB, measure before second diagnostic SNRB
T1b = optional measure 1 week after second diagnostic SNRB, measure before third diagnostic SNRB
T2=measurements 1 week after diagnostic SNRB, just before segmental nerve intervention

T3=measurement 4 weeks after segmental nerve intervention

This study will include 50 patients and 50 age and gender matched controls.





Patients will receive care as usual. Segmental nerve intervention will be performed according to the standard procedures of the Anesthesiology Pain Center of the University Medical Center of Groningen:



dSNRB (diagnostic Sensory Nerve Root Block):

- Bupivacaine 0,75% 0,3ml with Visipaque 320 mg I/ml 0,3ml (total 0,6ml). Inject 0,35 – 0,55 ml in total



tSNRB (therapeutic Sensory Nerve Root Block):

-L3 and lower: Bupivacaine 7,5mg + Triamcinolon 40mg + Visipaque 320 mg I/ml together in one 5 ml syringe.

L2 and higher: Bupivacaine 7,5mg + Dexamethason 5mg + Visipaque 320 mg I/ml together in one 5 ml syringe.



pRF (pulsed RadioFrequency):

pulsed radiofrequency (20msec on, 480msec off)

on 45V during 4 min, temp <42 degrees Celcius





Pain and Quality of Life parameters will be collected to assess and quantify central sensitisation during several stages of the care as usual procedure.



Healthy control subjects will not receive any segmental nerve intervention, but will perform all other measurements on given timepoints.