Occipital Nerve Stimulation in Medically Intractable Chronic Cluster Headache

Trigeminal autonomic cephalalgias (TACs) are characterized by frequent, short-lasting attacks of unilateral extremely severe headaches accompanied by ipsilateral facial autonomic features and are the most severe of the primary headache disorders. TACs include cluster headache (CH), paroxysmal hemicrania (PH) and short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT). CH is the most common form of TAC. The 1-year prevalence is about 1 in 1000, with the vast majority of patients having episodic CH (ECH): periods of weeks to months with frequent attacks which are alternated with symptom-free periods of several months to years. About 10% have chronic CH (CCH): attack free periods of less than one month in every 12 months, unless treatment is given. The chronic form can be primary unremitting from onset, or can be secondary, transform from the episodic form. CCH may spontaneously become episodic.

Effective acute treatments for CH attacks are injectable or intranasal triptans and oxygen inhalation. Steroids (only for a short period), verapamil, lithium carbonate and methysergide are the most effective preventive therapies. At least 10% of patients with CCH is or may become refractory to or cannot tolerate medical therapy. For patients with medically intractable CCH (MICCH) there is no common treatment. Different experimental treatments, such as deep brain stimulation (DBS), radiofrequency lesions, glycerol injections, gamma knife, and surgery or root section of the trigeminal nerve are either substantially ineffective, or have significant short-comings with serious complications such as death or neurological deficits such as anaesthesia dolorosa or lack of efficacy.

CH has considerable impact on socio-economic and personal functions due to direct costs of healthcare services and indirect costs of lost work days and decreased work efficacy. Higher pain scores and a higher percentage of patients with poor health due to pain and social functioning are found among CH patients compared with patients suffering from migraine. The impact on social functions, quality of life and use of healthcare of patients with MICCH is most likely even larger, although precise figures are not available. In the study of Burns et al. patients, suffering from MICCH, had on average over four attacks per day. Attacks of CH have been described by patients as being worse than child birth. Recently treatment of headache was listed as one of the top priorities of US National the Institute of Medicine's agenda for comparative-effectiveness research.

Functional imaging studies in CH identified activations in the region of the posterior hypothalamus, which led to the use of neurostimulation therapy in MICCH. Hypothalamic DBS was shown to be effective in some patients with MICCH but unfortunately this treatment is associated with a high risk of (even lethal) consequences.

Structures in the occipital region of the head are mainly innervated by the greater occipital nerve that is a branch of the C2 spinal root. Convergence of cervical, somatic trigeminal and dural trigeminovascular afferents on second order nociceptors in the brain stem is well documented. Stimulation of the greater occipital nerve increased metabolic activity in cervical regions of the spinal cord and in the trigeminal nucleus caudalis in the cat. In humans an occipital nerve blockade decreased the ipsi- and contralateral R2 response, confirming the anatomic and functional convergence of afferent cervical and trigeminal pathways. These studies suggest that modulation of these pathways may influence headache.

Suboccipital injection of corticosteroid with local anaesthetics was shown to be effective in a placebo-controlled trial. In this study 4 patients suffering from CCH were included. In all patients the attacks recurred eventually. The authors suggest that suboccipital steroid injections ought to be tried as a single shot treatment before invasive treatments are considered such as DBS, but in later studies this turned out to be of no predictive value of the response to neuromodulation therapies.

Along the same line, stimulation of the greater occipital nerve (ONS) has been tried with some success in intractable headaches including CCH. Burns et al. described 14 patients suffering from MICCH and were treated with ONS in an open retrospective study. Ten patients improved; three improved by 90% or more, 3 by 40%-90% and 4 by 20-30%. In a prospective open ONS study on MICCH patients Magis et al. showed a reduction in attack frequency of 79.9%. No serious complications were described in both studies.