Radiofrequncy Ablation in Chronic Pain Management

1. Radiofrequncy Ablation in Chronic Pain Management Joel Chang MD

2. CASE • 67 y/o M • Lumbago, facet arthropathy, lumbar spondylolithesis, post-laminectomy • Attempted Tx: TENS, PT/ aqua, lidoderm, oxycontin, epidural • 2 Lumbar MBBs of L3-S1 with about 1 hour relief each time • Presented for pulsed radiofrequency ablation of L3-S1 of right MBs

3. Overview • RFA is indicated for pain with constant and limited distribution • Interrupts nociceptive pathways in the treatment of chronic pain • Useful for nociceptive pain and some neuropathic pain • Diagnosis confirmed with diagnostic blocks first • Tendency for recurrence 1-2 years but can be repeated

4. Non-indications • Centralized pain • Pathology in the spinal cord • Serious Psychopathology

5. Diagnosis • Diagnostic blocks are usually done before RFA • Done only if blocks are expected to provide information (ex: herniated disc) • Diagnostic block utility include trigeminal neuralgia, and lumbar and cervical facet joint pain

6. Diagnostic Injections • Studies showed that single diagnostic lumbar z joint blocks are false positive 38% of the time. Blocks are usually repeated as a result • The International Association for the Study of Pain specifies that diagnosis requires radiographically guided blocks provide complete relief and are validated by a appropriate control test that exclude false-positive responses

7. RFA Sites • Medial Branch of Posterior Ramus: innervates the facet joints • Dorsal Root Ganglion (herniated discs or regional pain syndromes) • Intradiscal RF • Sympathetic chain • Splanchnic nerve • Gasserian ganglion for trigeminal neuralgia

8. RF Machine • Includes temperature display, impedance monitor, stimulator, and lesion generator. • Impedance Monitor: Useful for detecting entry into various mediums ( a large increase for example might suggest movement from fluid to tissue) • Electrical Stimulation: Sensory stimulation confirms proximity to the target. Motor stimulation confirms a safe distance to motor fibers in case a heat lesion is made • Lesioning Module: continuous vs pulsed RF

9. RF Machine (cont) • When the electrode is placed on the patient’s body, a circuit is complete • An electric field is established around the electrode tip. This field oscillates with alternating RF current causing movement of ions in the tissue • This causes friction in tissue surrounding the catheter tip which produces heat (not the catheter itself) • Monitoring the catheter tip temp therefore adequately measures tissue temp.

10. RF Machine (cont) • RF current is low energy, high frequency (100,000-500,000 hz) • RF lesions do not selectively destroy only nociceptive afferents • Temperature determines the size of the lesion • Cells become damaged at temps 42 to 45 degrees celsius. With temps of 60-100 degrees celsius there is near instantaneous induction of protein coagulation, leading to cell death • Electrical stimulation at 50 hz should produce sensory stimulation at less than 1 V if electrode is placed correctly. • Stimulation at 2 hz should evoke contraction of ipsilateral paraspinal muscles below 2.5 V but without limb contracture.

11. RF tidbits • RFA near bone or scar tissue may have a very irregular ablation pattern from differences in impedance and conductivity leading to complications. Pulsed RFA is more ideal in these situations and less likely to lead to complications • Patients with pacemakers: cardiology consultation is needed to convert the pacemaker to a fixed rate for the procedure • Patients with spinal cord stimulators: adjustments are also needed with the settings (monopolar needs to be changed to bipolar and off)

12. Technique • RF electrodes produce little lesion distal to their tip and coagulate transversely • Therefore if electrodes are placed perpendicularly to the nerve the may fail to coagulate the nerve or will coagulate the nerve minimally • The most reliable coagulation is done if the electrodes are placed parallel to the nerve. • Of note that some of the early studies were believed to be done under poor technique, producing poor outcomes • Needless to say, outcome results depend on user experience with RFA

13. Technique (cont) • The use of preliminary electrical stimulation of the medial branch nerve to verify electrode placement is debatable. • Some argue its an unnecessary use of time and that adjusting the electrode position to minimize the threshold for evoked activity does not improve outcome • Radiological confirmation of electrode placement is essential

14. Pulsed-RFA • RFA: 80 degrees C for 90 seconds • Pulsed-RFA: 42 degrees for 120 seconds • Current is applied in bursts of 20 ms with a silent time of 480ms • Lower temp in pulsed-RFA results in less tissue destruction • Unclear Mechanism of pulsed RFA: - modulates pain processing mechanisms -selectively disrupts small nerve fibers - Pulsed RFA associated with increased cFos

15. Pulsed- RFA • Studies show that PRF for lumbar facet joints tend do have a shorter benefit of pain relief (4 months compared to 12 months for RF) • Standard RF also denervates the multifidus muscle which eliminates the muscular component of lumbar facet syndrome

16. Results • Success for Lumbar RFA ranges from 60-90% • 21% had complete pain relief and 65% reported mild to mod pain relief • Other studies showed that 60 percent of patients enjoy at least 80% relief at 12 months and 80 percent enjoy at least 60 percent relief. • 92% achieved good relief for Trigeminal Neuralgia • Reports show that there is some loss of effect over 1-2 years • Can be repeated

17. Cervical RFA • Symptoms that indicate a patient might benefit from cervical RFA include: neck pain, headache, shoulder pain, scapula and upper arm pain • Cervical MBB have a false positive rate of 1 in 3 (lower than Lumbar but still requires diagnostic blocks) • A high failure rate noted for C2-C3 Z joints 2/2 nerves larger size and more variable course. This facet is innervated by the medial branch of the C3 dorsal ramus with a inconsistent contribution from the greater occipital nerve. • Cervical anatomical variability necessitates multiple RF lesions per target nerve • When pain reoccurs procedures can be repeated • Side effects are well tolerated and serious complications have not been reported

18. Other Applications • RFA MB of thoracic Z joint pain, but evidence not as reassuring • Also evidence for sacroiliac joint also not strong

19. Repeat RFAs • Study of effectiveness of repeat radiofrequency neurotomy for lumber facet pain (Schofferman, Kine, Spine Vol 29) showed that the frequency of success and durations of relief remained consistent after each subsequent radiofrequency ablation. • Mean duration of 10.5 months and successful more than 85% of the time • This 10.5 months however, is shorter than reported 1st time RFA relief

20. To Keep In Mind • RFA significantly improves the pain and quality of life in patients • However, it does not cure the (facet) pain.

21. References • Lord, S, Bogduk, N. Radiofrequency procedures in chronic pain. Best Practice and Research Clinical Anesthesiology Vol. 16, No. 4, 597- 617. • Mikeladze, Espinal, et al. Pulsed Radiofrequency application in treatment of chronic zygapopyseal joint pain. The Spine Journal 3 (2003) 360-362. • Niemisto, Kalso, et al. RF Denervation for Neck and Back Pain: A Systemic Review Within the Framework of the Cochrane Collaboration Back Review Group. Spine Vol 28, Number 16, pp 1877-1888. • Sluijter, M., Racz, G. Technical Aspects of Radiofrequency. Pain Practice, Vol 2, Number 3, 195- 200.