How Common Is Hemicrania Continua? Age and Sex Patterns

Hemicrania continua is a very rare headache disorder ^[1]. It is characterized by persistent, strictly one-sided head pain with severe exacerbations, along with other symptoms. Because it is so rare, demographic patterns can provide helpful context for researchers, but a person’s age or recorded sex cannot confirm or rule out the condition.

How Rare is Hemicrania Continua?

Studying exactly how many people have a rare condition is difficult. Different studies use different methods and timeframes, which means their estimates cannot be directly combined into a single range. The most robust recent studies provide estimates of its prevalence (the number of people who have the condition during a specific time):

Currently, large population studies have not provided a well-established estimate for the incidence of hemicrania continua (the rate of newly diagnosed cases per year) ^[1][2].

If you are being treated at a tertiary headache clinic (a specialist center for complex or difficult-to-treat headaches), the condition might seem more common. However, the high frequency seen in specialty clinics reflects a highly selected group of patients, rather than the general public ^[3][4].

Who is Most Affected?

Sex Recorded in Studies

Hemicrania continua affects women more frequently than men ^[1][2]. In specialized clinical samples, researchers report a female-to-male ratio ranging between roughly 3-to-1 and 4.5-to-1 ^[5][6]. However, these ratios come from selected clinic populations and may not perfectly represent everyone with the condition.

Age of Onset

The exact age when the headaches first begin is not clearly established by large population studies ^[7]. Most research records a patient’s age when they are evaluated in a specialist clinic, which averages between 37 and 52 years old ^[7][5]. While primarily diagnosed in adults, it can occasionally occur in children, though pediatric cases are exceptionally rare ^[8].

Why is the Data Limited?

Getting exact numbers is challenging due to several overlapping issues:

• Diagnostic Delays: Because the condition is rare, many patients go years without an accurate diagnosis. In some small clinical samples, the average delay from symptom onset to diagnosis was reported to be roughly 8 years ^[9].
• Misdiagnosis: The persistent, mild background pain is sometimes overlooked by doctors, while the severe pain spikes can be mistaken for migraines or cluster headaches ^[9]. Exacerbations often include migraine-like features or autonomic symptoms (like same-side eye watering or nasal congestion), adding to the confusion ^[9].
• Strict Diagnostic Criteria: The official diagnostic criteria (the specific symptom features clinicians use to make a diagnosis) require an “absolute” (complete) response to a medication called indomethacin ^[10]. However, indomethacin testing protocols vary. Different clinics use different doses, which can affect who receives an official diagnosis ^[10][11].
• Evolving Definitions: The medical criteria used to define hemicrania continua have changed several times over the decades, making it harder for researchers to compare older studies with newer ones ^[9][3].

Important Note on Indomethacin and Safety

An “absolute” response to indomethacin is just one part of a broader clinical assessment ^[10]. It must be considered alongside your specific headache pattern and the exclusion of other conditions. A negative trial could simply mean the dose was too low, the duration too short, or that a different condition is present.

Never start, borrow, or adjust the dose of indomethacin without direct medical supervision. Indomethacin is a potent prescription anti-inflammatory drug that carries serious risks, including gastrointestinal ulcers and bleeding, kidney injury, blood pressure elevation, and cardiovascular complications. Your doctor will carefully monitor your trial and may prescribe a second medication to protect your stomach lining.

Red Flags: When to Seek Urgent Care

Hemicrania continua is typically a primary headache disorder, but persistent one-sided pain can also be a secondary headache (meaning the headache is caused by another underlying medical condition, like a vascular issue or structural lesion) ^[12][13].

You should seek urgent or emergency medical evaluation if you experience any “red flag” symptoms, such as:

• A sudden, severe “worst-ever” headache
• Rapidly worsening pain or a change in your usual headache pattern
• New neurological symptoms (like weakness, numbness, or vision loss)
• Confusion, fever, or neck stiffness
• A new headache following a head injury
• A new headache during pregnancy or postpartum

While demographic data can help researchers understand the disease on a population level, it should never be used to dismiss your symptoms. If you have a persistent, strictly one-sided headache with exacerbations, your symptoms warrant a professional assessment regardless of your age or sex.