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.