Percutaneous electrical nerve stimulation for refractory neuropathic pain

Neuropathic pain means pain arising from dysfunction of sensory nerves and pathways in the nervous system. It may occur in a heterogeneous group of disorders: examples include painful diabetic neuropathy, post-herpetic neuralgia and trigeminal neuralgia. People with neuropathic pain may experience altered pain sensation, areas of numbness or burning, and continuous or intermittent evoked or spontaneous pain. Neuropathic pain is an unpleasant sensory and emotional experience that can have a significant impact on a person's quality of life.

A range of different drugs are used to manage neuropathic pain, including antidepressants, anti-epileptic (anticonvulsant) drugs, opioids, and topical treatments such as capsaicin and lidocaine (see NICE's guideline on neuropathic pain in adults: pharmacological management in non-specialist settings). Neuropathic pain is often difficult to treat, because it can be refractory to many medications and/or because of the adverse effects associated with some medications.

In percutaneous electrical nerve stimulation (PENS), 1 or more individual nerves or dermatomes are stimulated using needle probes. A single probe with a grounding pad or pairs of fine-gauge needles are inserted into soft tissue near the targeted nerves or into the affected dermatomes. The needles are connected to a low-voltage pulse generator and an electrical current is then applied. This may generate a sensation of paraesthesia and muscle contraction. The duration of treatment varies but each session of stimulation typically lasts between 15 and 60 minutes.

A crossover randomised controlled trial (RCT) of 64 patients comparing PENS against sham PENS or transcutaneous electrical nerve stimulation (TENS) in patients with pain from sciatica reported a significant reduction in pain after the last treatment session (measured on a visual analogue scale [VAS]; 0 to 10 from best to worse) compared with baseline in both PENS (from 7.2 to 4.1, p<0.05) and TENS (from 7.0 to 5.4, p<0.05) groups, but not in the sham-PENS group (from 6.6 to 6.1, p=not significant). The reduction in the PENS group was significantly greater than the reductions in the TENS and sham-PENS groups (p<0.01).

A crossover RCT of 50 patients with diabetic neuropathic pain in the legs comparing PENS with sham PENS reported a significantly greater reduction in pain (measured on a VAS; 0 to 10 from best to worse) in the PENS group (from 6.2 to 2.6) compared with the sham-PENS group (from 5.2 to 4.8) after the last treatment session (p<0.05).

The RCT of 64 patients reported a significant improvement after the last treatment session from baseline in physical activity (measured on a VAS; 0 to 10 from best to worse) in both the PENS group (from 6.4 to 4.0, p<0.05) and the TENS group (from 5.8 to 4.5, p<0.05) but not in the sham-PENS group (from 6.0 to 5.5, p=not significant). The improvement in the PENS group was significantly greater than in the TENS and sham-PENS groups (p<0.01).

The RCT of 50 patients reported baseline physical and mental component SF-36 scores of 31.2 and 41 respectively (mean scores taken 24 hours before the first treatment session). These scores increased to 36.8 (p<0.01) and 43.9 (p<0.01) respectively for the PENS group; and to 32.4 (p<0.05) and 42 (p<0.05) respectively for the sham-PENS group (these were mean scores taken 36 hours after the last treatment session). Improvement was significantly greater for the PENS group (p<0.05). In both RCTs of 64 and 50 patients, the post-intervention scores for PENS groups were still below the normal population score of 50.

The RCT of 64 patients reported a 50% reduction over 3 weeks in daily analgesic use with PENS treatment compared with TENS (29%) and sham PENS (8%; level of significance not reported).

The RCT of 64 patients reported a significant improvement from baseline in quality of sleep after the last treatment session (measured on a VAS; 0 to 10 from best to worse) in both the PENS group (from 5.5 to 3.1, p<0.05) and the TENS group (from 5.0 to 4.0, p<0.05) but not in the sham-PENS group (from 5.2 to 4.9, p=not significant). The improvement in the PENS group was significantly greater than the reductions in the TENS and sham-PENS groups (p<0.01). The RCT of 64 patients reported that most patients (73%) rated PENS as the most desirable treatment, compared with TENS (21%) and sham PENS (6%).

The Specialist Advisers listed key efficacy outcomes as reduction in pain (alleviation of localised neuropathic pain, relief of allodynia and hyperpathia, reduction in the frequency of sharp shooting pains, reduction in the burning sensation) and its associated functional and emotional improvements.

The RCT of 64 patients did not report safety findings.

The RCT of 50 patients and an RCT of 31 patients stated that no adverse events were reported.

The Specialist Advisers listed exacerbation of pain, bruising and bleeding as anecdotal adverse events. They listed theoretical adverse events as vascular damage; damage to local nerves with sequelae, depending on which nerve was damaged; pneumothorax; possible interaction with a cardiac pacemaker if used above the waistline; possible epileptogenic effect if used near the head; possible effects if used in pregnancy; dislodgement (with loss of effect); unpleasant paraesthesias; and local bruising or haematoma.

The Committee noted that clinical response to treatment with PENS may differ according to the indication treated.

The Committee recognised that the numbers of patients in the RCTs were relatively small, but the evidence of efficacy in relieving pain was consistent. No major safety concerns were raised by the trials or the Specialist Advisors, or in the Committee's judgement of likely risks. Patients being considered for this procedure are often distressed by chronic pain that has been refractory to other treatments. The Committee therefore considered that the balance of benefits and risks justified a recommendation for use of this procedure with normal arrangements for clinical governance, consent and audit, in the context of patient selection by teams specialising in pain management.