2 The procedure
2.1.1 TACs (for example cluster headaches) are characterised by relatively short-lasting but severe pain attacks associated with autonomic manifestations such as sweating, flushing, and ipsilateral rhinorrhea.
2.1.2 The first-line treatment for TACs is usually medical therapy, carried out with the aim of either preventing or limiting the duration of episodes. Surgery to interrupt the trigeminal sensory or autonomic pathways is sometimes used, but this has a risk of serious complications including diplopia and corneal ulcers.
2.2.1 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 the pain signals.
2.2.2 DBS for intractable TACs is usually carried out with the patient under local anaesthesia and/or intravenous sedation. 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.
2.2.3 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'.
Sections 2.3 and 2.4 describe efficacy and safety outcomes from the published literature that the Committee considered as part of the evidence about this procedure. For more detailed information on the evidence, see the overview.
2.3.1 A crossover randomised controlled trial (RCT) of 12 patients with refractory chronic cluster headache (CH) reported that there was no significant difference between the 'on' and 'off' periods in either the 'on–off' group or the 'off–on' group for a number of outcomes including frequency of attacks, pain intensity and patient satisfaction.
2.3.2 During a 10-month open phase of the RCT of 12 patients, when all patients received DBS, the mean weekly attack frequency decreased by 48% from baseline (from a median of 14 to 8 attacks per week; p = 0.08).
2.3.3 A case series of 20 patients reported that all 16 patients treated for refractory chronic CH had relief from pain at a mean follow-up of 23 months. Time to response occurred at a mean of 42 days (range 1 to 86 days) with mean 71% of pain-free days.
2.3.4 The RCT of 12 patients reported reduced Hospital Anxiety and Depression Scale scores (7 anxiety items and 7 depression items with scores greater than 7 indicating anxiety and depression, respectively) in the open phase only. Median anxiety scores decreased from 13 to 7.5 (p = 0.008) and median depression scores decreased from 10 to 4.5 (p = 0.052).
2.3.5 The Specialist Advisers listed key efficacy outcomes as improvement in the number of headaches, severity and duration of attacks, and quality of life, measured by headache scoring systems.
2.4.1 In a case series of 6 patients with unilateral refractory chronic CH, 1 patient died 3 days after the procedure from an intracerebral haemorrhage which developed along the lead tract a few hours after the procedure.
2.4.2 The RCT of 12 patients reported subcutaneous infection 3 weeks after surgery in 1 patient, and the case series of 21 patients reported 1 occurrence of deep infection. Both resolved after hardware removal and antibiotic treatment.
2.4.3 In the RCT of 12 patients, 1 patient developed transient loss of consciousness with hemiparesis shortly after test stimulation and subsequent severe micturition syncopes associated with a decrease in blood pressure in the standing position (not otherwise described).
2.4.4 The case series of 6 patients reported that all patients had diplopia and dizziness if high levels of electrical stimulation were used (above 1.5 V). One patient became tachypnoeic and tachycardic but symptoms resolved after the recording electrode was removed.
2.4.5 The Specialist Advisers listed anecdotal adverse events as stroke, seizures and lead migration.
2.5.1 The Committee found interpretation of the evidence difficult: the single RCT dealt only with a subgroup of patients.
2.5.2 The Committee noted patient commentary, which reported improvements in quality of life, even if pain was relieved only partially, and noted that some patients were no longer suicidal after treatment.