What is headache?

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What is a Headache?

A headache is pain or discomfort located anywhere in the head, scalp, or upper neck region - it's one of the most common symptoms in medicine and can range from a trivial, self-limited nuisance to a warning sign of serious underlying disease.

Classification

Headaches are broadly divided into two categories:

1. Primary headaches - the headache itself is the disease, with no underlying structural or systemic cause. The main types are:

Migraine - typically unilateral, moderate-to-severe, pulsating pain, worsened by routine physical activity, and accompanied by nausea/vomiting and/or photophobia/phonophobia (Goldman-Cecil Medicine).
Tension-type headache - a mild-to-moderate, holocranial (band-like, bilateral) headache without nausea or vomiting; patients may have photophobia or phonophobia but not both (Goldman-Cecil Medicine).
Cluster headache and other trigeminal autonomic cephalalgias - unilateral headaches associated with ipsilateral autonomic features (tearing, nasal congestion, ptosis) (Goldman-Cecil Medicine).
Chronic daily headache - not a distinct disorder itself, but defined as headache occurring on more than 15 days per month; it's often a complication of an underlying primary headache disorder.

2. Secondary headaches - caused by an identifiable underlying condition, such as:

Vascular events (subarachnoid hemorrhage/aneurysm rupture - classically a sudden "thunderclap" headache)
Intracranial mass lesions or raised intracranial pressure
Infection (meningitis, sinusitis)
Head/neck trauma
Medication overuse
Systemic illness (e.g., hypertension, pregnancy-related conditions like preeclampsia)

Red-flag features requiring urgent evaluation/imaging

According to Bradley and Daroff's Neurology in Clinical Practice, features that should prompt urgent workup (often MRI, sometimes with contrast) include:

New-onset severe headache with no prior headache history (especially "worst headache ever" or thunderclap onset)
Progressive increase in frequency or severity
Headache always localized to one fixed area
Headache that fails to respond to treatment
Headache in a cancer patient
Headache with fever, altered mental status, or a focal neurological deficit

Mechanism (brief)

Pain-sensitive structures in the head include the scalp, meninges (especially around blood vessels), venous sinuses, and certain cranial nerves (particularly the trigeminal nerve). Most brain tissue itself is insensitive to pain; headache arises from traction, inflammation, dilation, or irritation of these pain-sensitive structures rather than the brain parenchyma itself (Guyton and Hall Textbook of Medical Physiology).

If you're asking about a specific type of headache (migraine, tension-type, cluster, or a "red flag" presentation) or want details on evaluation/management, let me know and I can go deeper.

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