A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the pain-sensitive structures around the brain. Nine areas of the head and neck have these pain-sensitive structures, which are the cranium (the periosteum of the skull), muscles, nerves, arteries andveins, subcutaneous tissues, eyes, ears, sinuses and mucous membranes.
There are a number of different classification systems for headaches. The most well-recognized is that of the International Headache Society. Headache is a non-specific symptom, which means that it has many possible causes. Treatment of a headache depends on the underlying etiology or cause, but commonly involves analgesics.
There are over 200 types of headaches, and the causes range from harmless to life-threatening. The description of the headache, together with findings on neurological examination, determines the need for any further investigations and the most appropriate treatment.
The most common types of headache are the “primary headache disorders”, such as tension-type headache and migraine. They have typical features; migraine, for example, tends to be pulsating in character, affecting one side of the head, associated with nausea, disabling in severity, and usually lasts between 3 hours and 3 days. Rarer primary headache disorders are trigeminal neuralgia (a shooting face pain), cluster headache (severe pains that occur together in bouts), and hemicrania continua (a continuous headache on one side of the head).
Headaches may be caused by problems elsewhere in the head or neck. Some of these are not harmful, such as cervicogenic headache (pain arising from the neck muscles). Medication overuse headache may occur in those using excessive painkillers for headaches, paradoxically causing worsening headaches.
A number of characteristics make it more likely that the headache is due to potentially dangerous secondary causes; some of these may be life-threatening or cause long-term damage. A number of “red flag” symptoms therefore means that a headache warrants further investigations, usually by a specialist. The red flag symptoms are a new or different headache in someone over 50 years old, headache that develops within minutes (thunderclap headache), inability to move a limb or abnormalities on neurological examination, mental confusion, being woken by headache, headache that worsens with changing posture, headache worsened by exertion or Valsalva manoeuvre (coughing, straining), visual loss or visual abnormalities, jaw claudication (jaw pain on chewing that resolves afterwards), neck stiffness, fever, and headaches in people with HIV, cancer or risk factors for thrombosis.
“Thunderclap headache” may be the only symptom of subarachnoid hemorrhage, a form of stroke in which blood accumulates around the brain, often from a ruptured brain aneurysm. Headache with fever may be caused by meningitis, particularly if there is meningism (inability to flex the neck forward due to stiffness), and confusion may be indicative of encephalitis (inflammation of the brain, usually due to particular viruses). Headache that is worsened by straining or a change in position may be caused by increased pressure in the skull; this is often worse in the morning and associated with vomiting. Raised intracranial pressure may be due to brain tumors, idiopathic intracranial hypertension (IIH, more common in younger overweight women) and occasionally cerebral venous sinus thrombosis. Headache together with weakness in part of the body may indicate astroke (particularly intracranial hemorrhage or subdural hematoma) or brain tumor. Headache in older people, particularly when associated with visual symptoms or jaw claudication, may indicate giant cell arteritis (GCA), in which the blood vessel wall is inflamed and obstructs blood flow.Carbon monoxide poisoning may lead to headaches as well as nausea, vomiting, dizziness, muscle weakness and blurred vision. Angle closure glaucoma (acute raised pressure in the eyeball) may lead to headache, particularly around the eye, as well as visual abnormalities, nausea, vomiting and a red eye with a dilated pupil.