Deep brain stimulation for refractory chronic pain syndromes (excluding headache)

Chronic refractory pain syndromes often have a complex natural history and unclear aetiology. Pain may be nociceptive, neuropathic or deafferentation or in some cases, of uncertain origin.

Treatment of chronic refractory pain usually includes physical, psychological and/or pharmacological treatments. Neurostimulation of the motor cortex, spinal or peripheral nerves have been introduced as treatment options for patients whose condition is unresponsive to other forms of treatment.

Deep brain stimulation (DBS) involves stereotactic targeting of specific anatomical sites within the brain (such as the sensory thalamus or periaqueductal grey matter) to modulate the central processing of pain signals.

With the patient under local anaesthesia and/or intravenous sedation, or general anaesthesia, electrodes are inserted into the brain using magnetic resonance imaging and/or computed tomography. A test stimulation (or macrostimulation) is used to check for side effects. Postoperative scans may be used to assess the position of the electrodes and to identify complications such as local haemorrhage.

Following satisfactory electrode testing, a pulse generator is implanted under the chest wall and connected by tunnelled wires to the electrodes. The generator usually remains switched 'on'.

A non-randomised comparative study of 43 patients with post-stroke pain treated by DBS or motor cortex stimulation reported pain reduction greater than 60% in 25% (3 out of 12) and 48% (15 out of 31) of patients respectively (measured on a visual analogue scale [not described]; follow-up not stated).

A case series of 112 patients with chronic intractable deafferentation pain reported that 47% (42 out of 89) of patients were pain-free and 32% (28 out of 89) of patients were 'improved' at follow-ups ranging from 6 months to 6 years. The procedure was considered to have failed in the remaining patients (21% [19 out of 89]).

A case series of 122 patients reported treatment success (defined as the patient being able to control their pain using the device with or without medication) in 77% (50 out of 65) of patients with severe intractable pain of peripheral origin (follow-up not stated).

The Specialist Advisers listed key efficacy outcomes as a reduction in frequency and severity of pain, improvement in physical and mental function, improvement in quality of life, and reduction in medication requirements.

Intracranial haemorrhage was reported in 4% (5 out of 141) of patients (timing of events not stated) in a case series of 141 patients with nociceptive or deafferentation pain; 1 patient died and 4 patients had neurological deficits, of whom 2 recovered completely and 2 were left with significant deficits.

The case series of 122 patients reported 2 deaths: 1 due to massive cerebral oedema and haematoma in the basal ganglia and the other to coronary occlusion occurring 9 weeks after ventricular haemorrhage (a complication of the procedure).

The case series of 141 patients reported infection in 12% (17 out of 141) of patients (23 cases). Of these, 12 cases occurred within 30 days of the procedure and 10 cases were reported after 30 days (1 case not described). One patient was successfully treated with antibiotics alone, 2 with antibiotics and debridement, and 11 with antibiotics and electrode removal (3 patients not described).

The case series of 122 patients reported ventriculitis in 1 patient, subgaleal infection in 4 patients and subdural empyema in 1 patient. The patient with ventriculitis and 3 of those with subgaleal infection were successfully treated with antibiotics, but the remaining 2 patients required removal of the DBS system.

The case series of 141 patients reported erosion of hardware in 7% (10 out of 141) of patients. Of these, 5 patients had the DBS system removed and 5 had successful re-implantation without the need for antibiotics. Electrode migration occurred only with early versions of the electrodes.

The Specialist Advisers listed anecdotal adverse events as suspected development of a new neuropathic pain condition after migration of the lead, mood change from aberrant stimulation, stimulation-induced reversible side effects such as dysarthria, and seizures. The Specialist Advisers considered theoretical adverse events to include cerebral infarction.

The Committee noted that the available studies described heterogeneous treatment protocols and patient groups. In addition, most were published some years ago and DBS techniques have evolved. These factors made interpretation of the evidence difficult. The Committee considered that there was insufficient evidence to assess efficacy in different patient groups.

The Committee noted strongly positive commentaries from patients who had been treated by DBS; some described how even partial relief of their pain had resulted in significantly improved quality of life.