Hemicrania Continua (HC) is a rare headache disorder characterized by persistent pain on one side of the head. The term is derived from the Greek hemi (half) and crania (head), combined with the Latin continua (continuous). HC is defined by a strictly unilateral, or “side-locked,” headache that is present every day, all day, for at least three months. HC is considered a primary headache disorder, meaning the pain is not a symptom of another underlying condition.
Defining Characteristics and Associated Symptoms
The defining pain of Hemicrania Continua is two-fold: a continuous background pain with superimposed severe flare-ups, known as exacerbations. The baseline pain is typically described as a dull, aching, or pressing sensation, ranging from mild to moderate in intensity. This persistent discomfort distinguishes HC from headaches that include pain-free periods.
Patients experience several daily exacerbations where the pain abruptly increases in intensity, often becoming throbbing or stabbing and reaching severe levels. During these flare-ups, specific cranial autonomic features appear on the same side of the head as the pain. These features reflect a temporary overactivity of the parasympathetic nervous system.
The autonomic features that accompany the pain exacerbations include:
- Tearing (lacrimation) and redness of the eye (conjunctival injection).
- Nasal symptoms, such as a runny nose (rhinorrhea) or nasal congestion, occurring on the painful side.
- A drooping eyelid (ptosis) or a constriction of the pupil (miosis).
Some individuals also experience migrainous symptoms like sensitivity to light or sound, or feelings of agitation and restlessness during these intense periods.
Understanding the Classification and Rarity
Hemicrania Continua is classified as a primary headache disorder. It belongs to the group called Trigeminal Autonomic Cephalalgias (TACs), which are characterized by unilateral head pain combined with cranial autonomic symptoms. Other TACs include cluster headache and paroxysmal hemicrania, but HC is unique due to its continuous nature.
HC is considered a rare condition, though its exact prevalence is difficult to determine and it is often underdiagnosed. Estimates suggest HC may account for around one percent of all headache cases seen in specialized clinics. The rarity of the disorder means Hemicrania Continua is frequently misidentified.
The continuous pain profile often leads to an initial misdiagnosis of chronic migraine or chronic tension-type headache. The time from symptom onset to a correct diagnosis can span many years due to a lack of awareness among general practitioners. Recognizing the specific combination of continuous unilateral pain and ipsilateral autonomic features is the first step in distinguishing HC from other headache types.
Diagnostic Pathway and Testing
The diagnosis of Hemicrania Continua is primarily clinical, relying heavily on a detailed review of the patient’s symptoms and history. A neurologist will establish that the headache has been strictly unilateral and continuous for at least three months, with superimposed exacerbations and associated autonomic features. A thorough patient history, often aided by a headache diary, is collected to confirm these specific patterns.
Before a definitive diagnosis of HC, it is necessary to rule out secondary causes of continuous unilateral headache that could mimic the symptoms. This ensures the headache is not the result of a structural problem in the brain or surrounding vessels. Brain imaging, such as Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scans, is typically required to exclude conditions like tumors, vascular malformations, or internal carotid artery dissection.
Once structural causes have been eliminated, the diagnosis moves forward with a therapeutic trial. The final confirmation of Hemicrania Continua rests not just on the symptom profile but on the patient’s reaction to a specific medication. This unique pharmacological response is the definitive step that separates HC from all other headache disorders.
The Definitive Treatment: Indomethacin
The most remarkable feature of Hemicrania Continua, and a mandatory diagnostic criterion, is its absolute response to the medication Indomethacin. Indomethacin is a nonsteroidal anti-inflammatory drug (NSAID) that provides complete or near-complete pain relief. This response is so specific to HC that it serves a dual purpose: it is both the treatment of choice and the diagnostic test.
The Indomethacin trial typically begins with a low dose, such as 25 milligrams, taken three times a day with food. The dose may be gradually increased, usually up to 150 milligrams per day, until the patient achieves complete pain freedom. A positive response means the pain significantly reduces or vanishes entirely, often within a few days of reaching the effective dose.
Because Indomethacin is an NSAID, long-term use carries a risk of gastrointestinal side effects, including irritation, gastritis, and peptic ulcers. Patients who require continuous treatment are often prescribed a protective medication, such as a proton pump inhibitor (like omeprazole), to minimize stomach irritation. Doctors aim to find the lowest effective maintenance dose to control the headache while reducing the risk of adverse effects.
While Indomethacin is the gold standard, some patients may not tolerate its side effects or have pre-existing conditions that prevent its use. Alternative treatments may be explored, including other medications like celecoxib (a different type of NSAID) or certain nerve blocks. However, the complete response to Indomethacin remains the defining characteristic of Hemicrania Continua.