Hemicrania Continua Flares: How Long, What Triggers Them?

Experiencing unpredictable, severe headache flares can be frightening and frustrating. If you have hemicrania continua, you might wonder what causes these sudden spikes in pain and how long they will last. It is important to know that a lack of an identifiable trigger is common, and spontaneous flares are a normal part of the condition rather than something you are doing wrong.

Hemicrania continua is formally diagnosed based on a specific persistent pattern: continuous, strictly one-sided background pain with superimposed severe exacerbations (flares), accompanied by specific physical symptoms, and an absolute response to therapeutic doses of a medication called indomethacin ^[1]. Because continuous unilateral headache can sometimes have secondary causes (meaning it is caused by another underlying medical issue), a doctor must rule out these other conditions before confirming a hemicrania continua diagnosis ^[1].

How Long and How Often Do Flares Occur?

The duration and frequency of exacerbations vary dramatically from person to person ^[2]. There is no single “standard” pattern, but clinical series report the following ranges:

• Duration: Flares can be as brief as a few seconds or, in some cases, last continuously for weeks ^[2]. Often, patients experience exacerbations that last for one to several hours at a time ^{[3] [4]}.
• Frequency: Some people experience more than 20 distinct exacerbations in a single day, while others might only have one severe flare every few months ^[2].

Note: While variability is normal for hemicrania continua, a clearly new, unusually prolonged, or substantially more severe headache should always be evaluated by a healthcare provider rather than assumed to be a normal flare.

What Does an Exacerbation Feel Like?

The constant background pain of hemicrania continua is generally described as mild to moderate ^{[2] [5]}. During a flare, the pain typically escalates to a severe level ^[6]. Alongside this intense pain, exacerbations often bring on additional symptoms that can make hemicrania continua mimic other headache disorders ^[7]:

• Cranial Autonomic Symptoms: These are physical symptoms that usually occur on the painful side of the head, such as eye tearing, redness of the eye (conjunctival injection), nasal congestion, a runny nose, or eyelid changes ^{[8] [9]}.
• Behavioral Symptoms: Many people experience a strong sense of physical restlessness or agitation during a flare ^{[10] [9]}.
• Migrainous Features: During a flare, you might experience nausea, vomiting, or an intense sensitivity to light (photophobia) and sound (phonophobia) ^{[5] [9]}. In some clinical studies, up to 70% of people with hemicrania continua reported symptoms during an exacerbation that met the diagnostic criteria for a migraine ^[5]. However, having these migraine-like features during a flare does not automatically mean you have a separate migraine disorder.

Triggers vs. Aggravating Factors

When severe pain hits, it is natural to look for a specific cause. However, most hemicrania continua flares start spontaneously ^{[1] [9]}. It is helpful to understand the difference between a spontaneous flare, an aggravating factor, and a medication complication:

• Spontaneous onset: An external trigger is not required for an exacerbation to happen ^[1].
• Aggravation by movement: While an activity may not trigger the headache disorder itself, routine physical movement or changes in position can sometimes aggravate or worsen the pain of an existing flare ^{[11] [12]}.
• Medication-Overuse Headache: Heavy or frequent use of acute pain relievers (analgesics) can sometimes increase your overall number of headache days and worsen your condition, a complication known as medication-overuse headache ^[13]. This does not mean an over-the-counter medicine directly caused a specific flare, but rather that it can worsen your overall headache burden. Risk thresholds differ by medication, so discuss your usage with your doctor. Do not abruptly stop prescribed medications without clinical advice.

⚠️ When to Seek Emergency Care

Because hemicrania continua involves continuous one-sided pain, it is crucial to know how to distinguish a familiar flare from a potential medical emergency. Seek urgent or emergency assessment if you experience:

• A sudden “thunderclap” headache (a severe headache that reaches maximum intensity within one minute)
• A headache accompanied by new neurological symptoms like weakness, numbness, confusion, fainting, or changes in speech or vision
• A headache with a fever, a stiff neck, or unexplained weight loss
• A persistent painful red eye or sudden vision loss
• A new headache following a head injury, or starting during pregnancy or the postpartum period
• A sudden, severe new headache triggered immediately by coughing or physical exertion
• A severe flare that does not respond to your clinician-prescribed emergency plan and is unusually prolonged

The Value of Tracking

If you suspect certain factors make your pain worse, track them in a headache diary ^[14]. Keep a record of your baseline pain, the exact start and stop times of your flares (or estimated times if exact tracking is impractical), your activities, any medications taken and their doses, and accompanying symptoms ^{[14] [15]}.

This diary is a helpful tool to identify patterns with your clinician, but it does not replace medical follow-up ^[14]. Avoid intentionally testing suspected triggers on your own ^[15]. Instead, share your observations with your care team to ensure your diagnosis remains accurate and your treatment plan is optimized.