Facing the shadows: Recognizing the pre-attack symptoms of cluster headache

Facing the shadows: Recognizing the pre-attack symptoms of cluster headache

A mother of three recently talked about fearing the pain of childbirth. She shared that before your first delivery, you’re afraid of what you don’t know. But the second time, she said, you’re afraid because of what you do know.

Such anxiety over anticipated pain sounds comparable to what some people experience during the pre-attack “shadows” of cluster headache. This disorder is perhaps the most severe of headaches and capable of being “many times more intense than a migraine attack,” according to the renowned Cleveland Clinic.1 Cluster headaches are distinguished by intense stabbing pain around one eye with autonomic reactions, like tearing, runny nose, and a drooping eyelid. Cluster attacks last 15 minutes to three hours and can happen up to eight times a day during an episode.2

Labelled as “shadows” in patient circles, the precursors of cluster attacks are essentially combinations of symptoms patients can experience that, according to author Ashley Hattle, “may warn them an attack is lurking or imminent.”3 Though limited, the available medical research reveals that about 60 to 80 percent of cluster headache patients can experience shadows. Researchers simply refer to them as pre-attack symptoms.4,5

The more we learn about the painful scourge of cluster headache, the easier it is to understand the anxiety and fear pre-attack symptoms can trigger. The feelings are best captured by reports from patients, like the one posted on Clusterheads: “For me all clusters start as a shadow. I consider it a shadow when the pain hasn’t blown up yet… It’s not really the pain that’s an issue with shadows, just knowing that at any moment it might turn into a full-blown attack. It’s like having a psychopathic sadist standing behind you, waiting for the right moment to attack, and the only thing you can do is hope that he goes away.”6

Until recently, very little medical research had been published to define the features of pre-attack symptoms for cluster headaches or the language used to describe them. Thanks to the publication of an important new study, it’s worth looking at the picture that medical experts are beginning to paint of pre-attack symptoms with an eye toward earlier intervention and potential moderation of attacks before they begin.

Illuminating the shadows

Patients talk about shadows. Medical experts and researchers refer to pre-attack symptoms. While they’re referring to the same phenomenon, it’s important for us to level-set what these terms mean.

On its web page that discusses some of the classic treatments for cluster headaches, the U.S.-based patient advocacy group Clusterbusters writes that “by shadows, we mean those mild, slightly painful but persistent feelings of cluster…sometimes right before an attack and serving as a warning.”7

Another definition posted on the online patient support group ClusterHeadaches.com goes beyond a broad description and the mere timing of symptoms to provide some detail on the substance of shadows.

“For my shadows,” the contributor writes, “an analogue is squeezing an orange. It feels like someone is squeezing the right half of my head, increasing the pressure…not so much pain as pressure. But then again, sometimes I’ll get a short jab with an icepick for 5-10 seconds. The only constant with these things is they change.” 8

In addition to variation within the same person, pre-attack symptoms can also differ from one cluster patient to the next. That’s why the newly published study we’ll discuss later in the post is so helpful. It establishes some unified characteristics to help better define what pre-attack symptoms look like. For now, the time-based description from that study should provide a sufficient medical definition by clarifying that “we refer to symptoms occurring minutes or hours before an attack as pre-attack symptoms.”4

Explaining where it hurts: Patient perspectives on shadows

While medical research gives us a clearer understanding of cluster headache shadows through the reporting and interpretation of data, the picture isn’t really complete without a sense of how pre-attack symptoms make patients feel both physically and emotionally.

The physical feeling of shadows

While pressure is one of the physical feelings some patients use to describe shadows, there is a full spectrum of physical manifestations. However, one constant in cluster sufferers’ descriptions of shadows is pain, which is noteworthy, because shadows are a precursor to the pain of a cluster attack and not the attack itself. Nevertheless, in research, cluster patients do delineate between the pain of pre-attack symptoms and cluster attacks themselves. This separation suggests the pain of shadows is somehow different from the pain of the actual cluster headache attack.

A description and a patient testimonial from the website for the Cluster Headache Support Group helps explain the perceived difference: “Although not part of the diagnostic criteria, many people living with cluster headache describe a low-level persistent headache that can be a precursor to full-blown cluster attacks. We call these ‘shadows.’ Read (these) patient descriptions…‘Shadow pain is what we call lower level pain that presents in the same location as your cluster headache, but is of a different nature…My husband describes a CH attack as feeling like a spike being driven into his skull. Shadow pain feels like a very painful bruise where the spike was.’”8

Thoughts and emotions about shadows

What’s most striking when reading patient accounts about the pre-attack symptoms of cluster headache is the strong sense of dread that can set in. Descriptions of the moment of realization that an attack is coming combined with narratives about the actual pain of “suicide headaches,” as cluster attacks have been labelled, give non-sufferers a glimpse of how life-altering cluster headaches can be. The accounts of shadows use a range of metaphors and analogies to convey the sense of anxious anticipation that can grip a sufferer.

Drawn from a lengthier account in one of the most sobering and personal depictions on the web of a cluster attack, this excerpt portrays shadows as a guard on watch, ready to warn the sufferer to brace for what’s ahead:

“I have become an expert at noticing when the attacks are about to hit. It is as though my perception has developed ‘sentinels’ to keep watch on the periphery of my senses. They alert me immediately the moment they notice the ‘Shadows.’ They sound the alarm and I begin to prepare myself for the attack, although there is little that can be done in way of preparation except to psyche myself up. I turn off the phones, draw the curtains, take a deep breath…”11

Another account turns to a more ominous image to help us comprehend the dread:

“Shadows are the symptoms of an oncoming attack and can be with or without low grade pain.  Like standing on the railroad tracks looking into the tunnel. You can feel the vibrations of the oncoming train. You can hear a dull roar, and catch a glimpse of the train’s light in the tunnel. Then you just wait.”8

And the relentless nature of cluster attacks combined with the pain they inflict has prompted many sufferers to describe the shadows like being in the grips of a merciless captor:

“The slightest twinge of discomfort, not pain, discomfort, starts at the base of your skull or in the depths of your temple. You stare straight ahead attempting to will it to stop here. Ten seconds pass, and a sharp knife begins to bore into your brain—as if someone was holding you hostage and threatening to stab right through your eye unless you comply…you realize that his intention is not to kill, but to torture.”3

Nevertheless, with all the anxious anticipation that pre-attack symptoms can trigger, a few patient accounts reveal that there may actually be a glimmer of hope amidst the shadows, if they’re seen as a warning to take action. In another excerpt from the same online discussion thread that referenced the squeezing of an orange and the oncoming locomotive, a veteran cluster sufferer wrote that “the best thing to take away from this thread is that a shadow…should be treated as soon as possible.”8

Another patient offers similar counsel to fellow cluster sufferers, even suggesting they might plan ahead and enlist the help of a friend or loved one in accessing and administering whatever abortive medication or therapy they use to provide fast relief during an attack:

“Most likely you have a ‘tell’ word such as ‘uh-oh,’ ‘oh no,’…If they can recognize that, they will know you are feeling the onset of an attack.  Have your spouse, son or daughter, roommate, etc. grab your abortive therapy while you hightail it to the oxygen tank.”3

These first-hand accounts from cluster headache sufferers are now supported by new medical research by headache experts. A team of Danish researchers are using the 2017 publication of their study on pre-attack symptoms as an opportunity to point cluster sufferers in the same direction, toward faster therapeutic intervention when recognizing shadows. Their study is giving cluster patients a clearer understanding of what pre-attack symptoms are and what their course looks like, so they can recognize them as early as possible and become proactive.

 Shedding light on the shadows: A welcome study assists with recognition

Published in 2017 in the international headache journal Cephalalgia, the study undertaken by researchers at the Danish Headache Center of the University of Copenhagen’s Department of Neurology was led by Dr. Agneta Snoer. The most comprehensive study to date of cluster headache’s pre-attack phase in a larger group of patients, its objective “was to describe the nature, prevalence and duration of pre-attack symptoms and signs in cluster headache.”9

The study observed 80 cluster headache patients, asking them about the presence of pre-attack symptoms in relation to what they considered to be a typical cluster attack. This observation included estimating the start and duration of each symptom prior to the attack, which was defined as the period when patients experienced severe or extremely severe pain in the area of the eye or temple, along with other symptoms and/or restlessness.

Among the study’s important results about pre-attack symptoms, Dr. Snoer and her colleagues found that:

  • Pre-attack symptoms happen frequently in cluster headache. In fact, they were reported by 83.3% of patients in the study with an average number of symptoms per patient of 4.25. The four most commonly reported symptoms were a dull/aching sensation (48.8%), shooting or stabbing pains (27.5%) in the area of the subsequent attack, difficulty concentrating (27.5%), and nasal congestion (23.8%).9
  • More than 60% of study participants experienced symptoms during the pre-attack period that the authors say confirm “the central role” the area of the brain known as the hypothalamus plays in cluster headache.9 The hypothalamic symptoms patients experienced the most included mood changes, difficulty concentrating, restlessness, yawning and light sensitivity (photophobia). Identifying these symptoms is important because, even though the exact biochemical cause of cluster headaches is not yet known, headache experts note that cluster headaches appear to originate in the hypothalamus. 2

In addition to documenting just how common pre-attack symptoms are among cluster patients, one of the tools the Snoer study produced that may be most useful for patients was a depiction of the most common pre-attack symptoms and how they progress before the actual onset of a cluster attack. (Figure 1)

Table 1. Progression of symptoms based on average duration prior to attack, as reported by study participants. 9

Looking at this progression, Snoer and her team observed that symptoms in the pre-attack period tended to follow a pattern, beginning with non-painful symptoms that are general in nature, meaning they affect the patient’s overall condition and are not localized to the eye and temple area that are the focus of cluster pain. These general symptoms include decreased energy level, mood changes, nausea, increased appetite, disturbed sleep, and restlessness.

Following the general symptoms were more localized and painful symptoms, like neck pain or a dull/aching sensation. And finally, many of the autonomic symptoms like tearing, runny nose and nasal congestion began in the last stages of the pre-attack phase, right before the onset of the attack.9

Being aware of this apparent pattern may be help patients more readily recognize the “shadows” when they come, potentially giving them more advance notice and time to prepare for an impending cluster attack.

Forecasting with shadows: Adding preparation to prediction

While the researchers of the Snoer study emphasize that further research is needed, their study confirmed that shadows or pre-attack symptoms are commonly experienced by cluster headache sufferers. Their observations also provide a better understanding of what the most common pre-attack symptoms tend to be and what the progression of those symptoms might look like in the hours and, especially, minutes before a cluster headache attack begins. And most importantly, the research team’s identification of these common pre-attack symptoms begins to lay a groundwork to help patients recognize key signs so they might apply their abortive therapy sooner in hopes of heading off or lessening the painful effects of cluster attacks that are on the horizon.9


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  1. The Cleveland Clinic Foundation. Cleveland Clinic Cluster Headaches Page. 1995-2017. Available at: http://my.clevelandclinic.org/health/articles/cluster-headaches.
  2. Hoffman, et al. Diagnosis, pathophysiology, and management of cluster headache. Lancet Neurol. 2018 Jan;17(1):75-83
  3. Hattle, Ashley. Cluster Headaches: A Guide to Surviving One of the Most Painful Conditions Known to Man. Pennsauken, NJ: BookBaby, 2017
  4. Snoer, et al. Pre-attack signs and symptoms in cluster headache: Characteristics and time profile. Cephalalgia. 2017; 0, p.1.
  5. Blau JN, Engel HO. Premonitory and prodromal symptoms in cluster headache. Cephalalgia. 1998; 18
  6. “Cluster v Shadow” post on Clusterhheads community of www.reddit.com. Available at: https://www.reddit.com/r/clusterheads/comments/3ce3xv/cluster_vs_shadow/
  7. Clusterbusters web site. Page on “Coping – Buster Friendly Treatments.” Available at: https://clusterbusters.org/treatment-options-busting/coping-buster-friendly-treatments/
  8. ClusterHeadaches.com “Re: What are ‘shadows’?” 10 June 2010. Web. Retrieved 27 Dec 2017 from: http://www.clusterheadaches.com/cgi-bin/yabb2/YaBB.pl?num=1276156003
  9. Snoer, et al. Pre-attack signs and symptoms in cluster headache: Characteristics and time profile. Cephalalgia. 2017 Jan 1
  10. Cluster Headache Support Group web site. Page on “What are Shadows?” Available at: https://chsg.org/education/what-are-shadows/
  11. Priest, S. (22 February 2009). Attack of the Shadows – a Cluster Headache experience. Retrieved from: http://mini-utopia.blogspot.com/2009/02/attack-of-shadows.html
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