The pain of cluster headaches is considered to be the worst of all headaches. Hence the moniker, suicide headaches. Thankfully, it is a rare condition. Episodic cluster headaches affect a little over 0.1% of the population or approximately 400,000 Americans. Of these, about 15% suffer from chronic cluster headaches. The division of cluster headaches into chronic and episodic is arbitrary, just like it is with migraines. Cluster headache attacks occurring for one year or longer without remission, or with remission periods lasting less than 3 months are considered to be chronic. Patients often go from episodic into chronic and back into episodic.

The term cluster comes from the fact that headaches occur daily or several times a day for a few weeks or months and then stop for a year or so. The attacks are always one-sided and the pain is localized around the eye. It can be associated with tearing, droopy eyelid, and nasal congestion on the side of pain. Some patients also have redness of the eye, sweating of the face, and tenderness in the back of the head.

These headaches are often misdiagnosed as migraine or sinus headaches. It can take several years before a patient receives the correct diagnosis and appropriate treatment.

The only FDA-approved preventive treatment is monthly injections of galcanezumab (Emgality). It came Verapamil, a calcium channel blocker used for hypertension, is another very effective drug. The dose of verapamil for cluster headaches is much higher than for hypertension – up to 960 mg a day. The only FDA-approved treatment for the treatment of individual attacks is sumatriptan (Imitrex) injections. Inhalation of pure oxygen through a mask at high flow (10-12 liters per minute) helps abort attacks in about 60% of patients. A course of steroids, such as prednisone, can sometimes stop the cluster period. These treatments are less effective for chronic cluster headaches.

Another treatment that can stop cluster attacks is an occipital nerve block. It is usually done with a steroid drug and a local anesthetic. The efficacy of this treatment led researchers to try electrical stimulation of the occipital nerve (ONS). It has been also tried in chronic migraines with mixed results.

Conducting trials of electrical stimulation presents big challenges. It requires surgical implantation of the stimulating wire next to the occipital nerve and the battery-operated device under the skin. It is impossible to disguise the sensation patients get from the electric current. They need to feel the stimulation in order for it to be effective.

A study just published in the journal Lancet compared strong and weak stimulation. The authors, led by Leopoldine Wilbrink, deserve great credit for conducting this difficult study. Despite the rarity of chronic cluster headaches, they were able to enroll 150 patients over a period of seven years. After a 12-week baseline observation, the patients were treated for 24 weeks.

The results showed that both weak and strong stimulation were equally effective. About half of the patients in each group had a 50% decrease in attack frequency. The most common side effects were local pain, impaired wound healing, neck stiffness, and hardware damage.

Another study by French researchers, Long-Term Efficacy of Occipital Nerve Stimulation for Medically Intractable Cluster Headache, was published last year in Neurosurgery. The mean duration of treatment observation was 44 months. Attack frequency was reduced by more than 50% in 69% of patients. Mean weekly attack frequency decreased from 22.5 at baseline to 10 after ONS. Functional impact, anxiety, and quality of life significantly improved after ONS. In excellent responders (59% of the patients), attack frequency decreased by 80% and quality of life dramatically improved from 38/100 to 73/100. 67 patients experienced at least one complication, 29 requiring an additional surgery: infection (6%), lead migration (12%) or lead fracture (4.5%), hardware dysfunction (8.2%), and local pain (20%).

ONS is a relatively safe treatment option for patients with chronic cluster headaches who do not respond to standard therapies. It is certainly safer than deep brain stimulation that has been reported to help some patients. Before resorting to ONS, I would also first try Botox injections, which I find to be effective in about a third of patients.

Besides ONS, vagus nerve stimulation (VNS) deserves further study. Two of my patients with severe chronic cluster headaches responded well to implanted VNS. This report led researchers to develop a non-invasive device to stimulate the vagus nerve. It was shown to be effective for episodic but not chronic cluster headaches. In my experience, however, it is only modestly effective even in episodic cluster headaches and is prohibitively expensive. The implanted VNS provides continuous stimulation. The non-invasive VNS is applied for only two minutes at a time. Future studies could compare the efficacy of ONS and implantable VNS.