Erfan Bashar
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Headache Classification

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Educational scope notice: This is a study note for medical students, not medical advice, diagnosis, or treatment guidance. Clinical management should follow local protocols and current guidelines.

Classification is the first safety step in headache. The clinician is not just naming a symptom; they are deciding whether the headache itself is the disease or a warning sign from another process.

A primary headache is a headache disorder in its own right. Migraine, tension-type headache, and cluster headache belong here. Primary headaches arise without a visible lesion on routine imaging: the nervous system misfires, sensitizes, or activates pain circuits in a stereotyped way. A secondary headache is attributed to another disorder, such as trauma, vascular disease including subarachnoid hemorrhage, tumor or raised intracranial pressure, infection, substance exposure, or cranial neuralgia. With secondary headache the clinical question becomes whether this headache behaves like the patient’s usual primary pattern or something new is happening.

The four primary headache families

The International Classification of Headache Disorders (ICHD) organizes primary headaches into four major families.

  1. Migraine is usually episodic, moderate to severe, often pulsating, and often accompanied by nausea, photophobia, phonophobia, and sometimes aura.
  2. Tension-type headache (TTH) is usually bilateral, pressing or tightening, mild to moderate, and not worsened by routine activity.
  3. Trigeminal autonomic cephalalgias (TACs) are short, severe, usually one-sided headaches with cranial autonomic signs. Cluster headache is the classic example.
  4. Other primary headaches include rarer syndromes such as primary cough headache, primary exercise headache, headache associated with sexual activity, hypnic headache, and primary thunderclap headache.

The term trigeminal autonomic cephalalgia (TAC) is worth unpacking. Trigeminal means pain in trigeminal nerve territory, often around the eye, forehead, temple, or face. Autonomic means the same side of the face may show tearing, red eye, nasal congestion, sweating, a small pupil, or a drooping eyelid.

Frequency changes management

Classification also asks how often attacks occur, because frequency changes treatment. Episodic migraine is treated attack by attack, often with non-steroidal anti-inflammatory drugs (NSAIDs) or triptans. Chronic migraine, usually defined as headache on at least 15 days per month with migraine features on at least 8 of those days, pushes toward preventive treatment. Tension-type headache is likewise divided into infrequent episodic, frequent episodic, and chronic forms, and chronic forms raise questions about medication overuse, comorbidity, sleep, stress, and central sensitization.

The “other primary headaches” group deserves caution rather than memorization. Primary thunderclap headache exists as a label, but thunderclap describes the speed and severity of onset, not the cause. Sudden maximal headache is secondary, meaning subarachnoid hemorrhage must be excluded, before any benign primary label is considered. The patterns behind each family are compared in /notes/neurology/migraine-vs-tension-type-vs-cluster-headache/ and worked through diagnostically in /notes/neurology/headache-diagnosis/.

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