Primer

Revolutionalising Chronic Pain Management

Radiofrequency neuro-ablation is the latest, safest and most effective method available to deal with many chronic pain conditions currently.

Dr Kailash Kothari

Pain is one of the worst enemies of human life. It is a well-known fact that each individual suffers pain in some or other form. About 70-80 per cent of population suffers from some kind of chronic pain (commonest being back/neck pain) at some stage during his/her lifetime. The World Health Organisation (WHO) has classified 'chronic pain' as a disease because of its widespread effect on patients' different body systems, psychology, and socio-economical effects.

How to Treat Pain

The treatment of pain starts from simple bed rest, analgesic medicines, physiotherapy to advanced methods of pain relief. The latest and most advanced technique include radiofrequency neuroablation (RF), cryoablation, laser, intra-spinal pump or stimulator implantations, and seven more techniques including minimally-invasive to major surgeries.

Here, I shall concentrate on RF, which is the latest, safest and most effective method available to deal with many chronic pain conditions currently.

RF is a neurolytic technique that uses heat to produce controlled tissue destruction (thermocoagulation) and thus reduce pain by modulating pain transmission, without causing clinical signs of nerve damage. Pain relief can last for several months before the procedure has to be repeated. RF is classified as a percutaneous minimal-invasive procedure for patients whose pain does not respond to appropriate medical and physical therapy.

During the procedure, an insulated needle is placed in the vicinity of the nerve to be lesioned. The needle position is checked, typically using multiple fluoroscopic X-ray views and by testing motor and sensory nerve stimulation. Once the correct position has been established, a grounded electrode is passed through the insulated needle to the tip. A current is then passed through the electrode, which heats up the surrounding tissue (because of the resistance produced by the body) and causes a lesion around the tip.

Types of Radiofrequency Neuroablation

There are two types of RF currently in use, continuous RF (CRF) and pulsed RF (PRF).

Continuous RF: It uses a constant output of high-frequency electric current to produce temperatures of 45?C or more (the temperature at which permanent nerve damage occurs), resulting in neuroablative thermocoagulation.

Pulsed RF: A more recent technique, PRF utilises brief 'pulses' of high-voltage, RF-range ( ?300 kHz) electric current to produce the same voltage fluctuations in the region of treatment that occur during CRF treatment, but without heating to a degree at which tissue coagulates. The heat generated is instead dissipated between pulses. PRF produces a transient inhibition of evoked synaptic activity and CRF produces a lasting inhibition.

Both CRF and PRF treatment induce distance-dependent tissue destruction under the stimulating needle, but the effect is more pronounced with CRF. On the other hand, the findings suggest that the acute effects of PRF are more reversible and less neurodestructive in nature than the classic continuous RF mode, even in normothermal conditions.

Mode of Action

The mode of action of RF has not yet been elucidated. Following are probable mechanisms:

• Thermocoagulation of nerve fibers (which denatures the nerves).
• Electric field created by RF current induces changes in the nerve cells and has a neuromodulatory effect on pain processing mechanisms at the dorsal root ganglion, dorsal horn, and molecular levels by changing gene expression in pain-processing neurons.
• PRF produces prolonged analgesia by inhibiting excitatory C-fibers via long-term depression.

Clinical Applications

RF is used for curing various conditions like:

Trigeminal Neuralgia (TGN): RF lesioning of V1 (only PRF), V2 or V3 (CRF) is an excellent choice for pain relief in TGN. It is day care, minimally-invasive, less costly and quite a safe method as compared to surgical decompression.

Headache: Many headaches are caused by upper cervical pathologies like facet joint pain syndrome, C1C2 neuralgias, and greater occipital neuralgia. These conditions can be diagnosed by specific fluoroscopic guided diagnostic nerve block. If pain relief is significant, RF is applied to give long-term pain relief in the following group of headache patients.

Chronic neck pain: Patients with chronic facet joint pain syndrome are treated with RF lesioning of medial branches of dorsal root. This is the only treatment available to deal with pain originating from facet joint. It gives dramatic relief in pain in most cases. Many intradiscal RF treatments are available to deal with herniated disc-related pain in neck and lower back. The same treatment is meted out to patients with chronic low back pain also.

Facial pain syndromes: Stellate ganglion and sphenopalatine ganglion are involved in many atypical and typical facial pain conditions. If diagnostic local anaesthetic injections give significant pain relief, RF lesioning is good option in these patients.

Postherpetic neuralgia (PHN): PRF lesioning of dorsal root ganglion (DRG) can be tried to relieve pain due to chronic PHN.

Others: Other applications of RF include that in complex regional pain syndrome (CRPS), previously known as reflex sympathetic dystrophy, diabetic painful neuropathy, pain due to vascular insufficiency, cancer-related pain and many more conditions.

Conclusion

RF is like stethoscope of the pain physician and this is a main weapon against pain in his armamentarium.

Its minimally-invasive character, target-selective approach, the possibility of outpatient treatment, and the relatively low incidence of side effects and complications-if carried out by a well-trained pain physician in the right setting—justify its use in patients refractory to conservative treatment prior to other more invasive, and often more expensive, treatment possibilities. The development of PRF, the minimally-neurodestructive isothermic application of an electric field to the target nerve structures, may open new and broader perspectives for RF treatment.

At present, RF treatment is available in few select centers across India, but its use will increase as more and more pain physicians will be trained in future.

The writer is Interventional Pain Management Specialist Wockhardt Hospital Mumbai
E-mail: drkothari@yahoo.com