What are the most common causes of hemicrania continua?

Most Common Causes of Hemicrania Continua

Hemicrania continua is an idiopathic primary headache disorder with no established secondary causes in most cases. While the etiology remains largely unknown, several potential secondary causes have been identified in case reports.

Clinical Features and Diagnostic Criteria

Hemicrania continua (HC) is characterized by:

• Persistent, strictly unilateral headache
• Moderate intensity with fluctuations
• Associated ipsilateral cranial autonomic symptoms
• Absolute response to indomethacin (diagnostic requirement)

Primary vs. Secondary Hemicrania Continua

Primary Hemicrania Continua

Primary HC is idiopathic and represents the vast majority of cases. It is diagnosed in approximately 1.8% of adult patients evaluated for headache in tertiary care settings 1.

Secondary (Symptomatic) Hemicrania Continua

While rare, several potential secondary causes have been documented:

1. Head Trauma

   • Post-traumatic HC has been reported in multiple cases where the onset was temporally linked to head injury 2

2. Cervical Arterial Dissection

   • Internal carotid artery dissection can present with a clinical picture mimicking HC 3
   • These cases may initially respond to indomethacin but require specific treatment for the underlying vascular pathology

3. Intracranial Pathology

   • Although not specifically mentioned in the provided evidence, case reports in the literature have linked HC-like presentations to:
     • Intracranial tumors
     • Cerebrovascular malformations

Clinical Variants

HC typically presents unilaterally, but atypical presentations have been documented:

• Bilateral HC: Cases of bilateral HC with required autonomic features have been reported, which still respond to indomethacin 4

Diagnostic Approach

When evaluating a patient with suspected HC:

1. Neuroimaging: Brain MRI with diffusion-weighted imaging is the preferred initial diagnostic test for patients with headache syndromes to exclude secondary causes 5

2. Vascular Imaging: Consider MRA or CTA of head and neck if there is:

   • Acute onset
   • History suggesting arterial dissection
   • Symptoms of posterior circulation involvement 5

3. Therapeutic Trial: A complete response to indomethacin (25-300 mg daily) is considered diagnostic 6

Management Considerations

• First-line Treatment: Indomethacin remains the gold standard treatment
• Alternative Treatments: For patients who cannot tolerate indomethacin, alternative options may be considered, though evidence is limited
• Secondary HC: If a secondary cause is identified, treatment should target the underlying etiology

Important Caveats

• The diagnosis of HC requires an absolute response to indomethacin, though the current diagnostic criteria lack clarity on what defines "absolute response" 1
• Autonomic symptoms in HC may be less pronounced than those seen in cluster headache 2
• A high index of suspicion for cervical arterial dissection should be maintained in patients with a clinical picture similar to HC, particularly with history of trauma 3

Despite being classified as a unique entity among primary headache disorders, HC shares features with trigeminal autonomic cephalalgias and chronic daily headaches such as chronic migraine and chronic tension-type headache 4.