EL Meyer, K Laurell, V Artto, L Bendtsen, M Linde, M Kallela, E Tronvik, JA Zwart, RM Jensen & K Hagen (2009) “Lateralization in cluster headache–a Nordic multicenter study”. J Headache Pain 10: 259-263 (click author to see paper)
AUTHORS’ ABSTRACT: A slight predominance of cluster pain on the right side has been reported in several studies. The aim of this large retrospective Nordic multicenter study was to estimate the prevalence of right- and left-sided pain in cluster headache (CH) patients with side-locked pain, the prevalence of side shifts in episodic and chronic CH patients, and the occurrence of cranial autonomic symptoms related to pain side. Among 383 cluster patients, 55 (14%) had experienced pain side shift. Of the remaining 328 individuals without side shift, there was no significant difference between the occurrence of right-sided and left- sided pain (54 vs. 46%). The prevalence of side shift was similar for episodic and chronic CH and the occurrence of cranial autonomic symptoms was not influenced by the pain side. In conclusion, previous reports of a side difference in location of cluster pain could not be confirmed in this large Nordic sample.
Dr. Sewell’s comment:
As we all know, cluster attacks occur on one side of the head only. In fact, I don’t believe I’ve ever seen or even heard of a cluster attack that happened on both sides at the same time. However, occasionally attacks can switch sides—when this does happen, it’s usually between one cluster period and another, but occasionally it can happen within a single cluster period. I had one patient once describe to me an hour-long cluster attack that finally started to die away—only to immediately start again on the other side! These researchers from Scandinavia decided that they wanted to find out more about on which side of the head the pain occurs in cluster headache, specifically asking three questions:
1. Do cluster attacks occur on the left and right side in equal numbers?
2. How often does the side of attacks shift in episodic patients, and is that the same for chronic patients?
3. Does the occurrence of cranial autonomic symptoms (runny nose, droopy eye, etc.) have anything to do with the side the pain occurs on?
This is not just a question of interest to ivory-tower academicians such as me, either—many extreme treatments for cluster headache (such as gamma knife, deep brain stimulation, trigeminal nerve cutting and so on) are done on one side, so it’s a mistake to use them if the attacks are switching back and forth.
To study these questions, the investigators took advantage of something that they have in Scandinavian countries, but not here: national registries for patients with different diseases. One hundred and twenty-seven patients came from Norway, 70 from Sweden, 132 from Denmark, and 15 from Finland; investigators didn’t even have to get in touch with any of them, since they had access to medical records and informed consent is not necessary for a chart review in Scandinavia.
What they found is interesting:
1. One in six cluster headache patients has experienced side shifts. This figure is the same regardless of whether the diagnosis is episodic or chronic.
2. Right-sided attacks are slightly more common (54% versus 46% for left-sided attacks). Unfortunately, these results didn’t reach “statistical significance”, meaning that the study didn’t have enough patients in it for the researchers to be at least 95% sure that the difference wasn’t just the result of random fluctuations. Interestingly, five other studies (reviewed by Ottar Sjaastad in his 1990 book, “Cluster Headache Syndrome”) ALSO show that cluster attacks occur 56% of the time on the right. The total number of patients in all of those other studies put together was 807, more than twice the number in this study. (And don’t forget, usually a right-sided neurological symptom implies a left-sided brain problem, because the nerve tracts cross in the brainstem, but this is not true for cluster headache—a right-sided cluster attack comes from the right hypothalamus.) What this all means is anybody’s guess!
3. Autonomic symptoms (runny nose, runny eye, droopy eye, etc.) were found in 96% of patients (which matches what other studies have shown—a tiny minority of cluster headache patients have just pain and nothing else when they have cluster attacks), and it didn’t seem to matter whether the pain was on the right, the left, or side-switching.
4. Most people had cluster periods lasting slightly over six weeks, but the authors did not give a range.
Eva Meyer, the first author of the study, is a relative newcomer to the cluster headache research world, having published her doctoral thesis only three years ago. Her work thus far has concentrated on hormonal abnormalities associated with cluster headache, so it’s hard to say what prompted her to do this study. It will be interesting to see what else she comes up with!