A Study Investigating the Efficacy of GON Blocks.

Greater occipital nerve block ("GON block") is carried out extensively in the treatment of chronic migraine, but more research is required to understand the effectiveness of the procedure. It consists of a superficial injection of local anaesthetic and steroid around a nerve at the back of the head that supplies sensation to part of the scalp. This study intends to provide more detailed information on the effectiveness, safety and tolerability of GON block with local anaesthetic and steroid in patients with chronic migraine. It does this by comparing it to a dummy (placebo) procedure (a needle is inserted near the nerve, but no therapeutic substance is injected). It is a "cross-over study": all patients will receive both the GON block and the dummy procedure (not necessarily in that order), with a period in between to assess the response to the first injection. The GON block will entail an injection of 2 mls of 2% lidocaine (a local anaesthetic) and 80 mg of DepoMedrone (a steroid) through a fine needle (a total of 4 mls). The dummy procedure will consist of an injection of 4 mls of normal saline (a solution of common salt and water) through a fine needle. Patients will be followed up at various time points throughout 6 months whilst being enrolled on the study.

Chronic migraine is characterised by frequency of headache ≥ 15 days per month for more than 3 months. The location can be unilateral or bilateral. Usually described as pulsating in nature, it may be aggravated by, or cause avoidance of, routine activities of daily living. There can be associated light and noise sensitivity. Greater occipital nerve (GON) blockade with local anaesthetics and steroids has been used as a preventative strategy for a range of headaches including, migraine, cluster headache and hemicrania continua.

The occipital nerves have a sensory distribution in the occipital area. The greater occipital nerve derives most of its fibres from the C2 dorsal root \[6\]. It passes over the superior nuchal line, mid-way between the mastoid process and the occipital protuberance, just lateral to the insertion of the nuchal ligaments. The lesser occipital nerve passes lateral to the greater occipital nerve, over the nuchal ridge. Although the exact mechanism of action remains unclear, injection of steroid in the vicinity of GON nerve can have both a local effect (decreasing nociception) and a delayed central nociceptive response, possibly through an action on trigeminocervical relay

Although GON block is carried out extensively in the prophylaxis of chronic migraine, the evidence remains equivocal. In the UK, the National Institute for Clinical Excellence have yet to include GON blocks in their guidance and protocols on the treatment of both chronic headache and migraine. This randomised, single-blinded, placebo-controlled multicentre cross-over study intends to assess the efficacy, safety and tolerability of greater occipital nerve block with local anaesthetic and steroid in patients with chronic migraine with the primary objective to investigate any improvement in disability associated with chronic migraine disorder. We also intend to identify any economic outcomes associated with these injections in the management of chronic migraine.

GON block with local anaesthetic and steroid for chronic migraine and the placebo procedure will be performed in the outpatient setting. They will be carried out only by appropriately qualified members of the research team adhering to strict aseptic conditions and following standard operating protocols with regards to admission and discharge criteria in the outpatient settings.

GON block is routinely carried out in the UK and poses minimal risks to the patient. Although GON block is carried out extensively in prophylaxis of chronic migraine, the evidence remains equivocal. In the UK, the National Institute for Health and Care Excellence (NICE) have yet to include GON blocks in their guidance and protocols on the treatment of both chronic headache and migraine.

The aim of this study is to assess the efficacy, safety and tolerability of greater occipital nerve block with local anaesthetic and steroid in patients with chronic migraine of more than three months' duration.

Eligibility Criteria:
Inclusion Criteria:

* Patients aged over the age of 18 who are able to provide a written consent
* Ability to read and write English, due to questionnaire use in study
* Diagnosis of chronic migraine with or without acute relief medication overuse (ICHD-III codes 1.3 and 8.2); as confirmed by diary documentation (headache on 15 or more days a month for at least 3 months)

Exclusion Criteria:

* Patient refusal
* Participation in any trial of any investigational products or interventional research project within the previous eight weeks to enrolment
* Patients unable to commit to the six-month study duration (PI judgment)
* Any known contraindication(s) to the IMPs as described by the manufacturer's Summary of Product Characteristics (SmPCs)
* Patients with a history of substance abuse
* Pregnant or breastfeeding patients