Headache fact file - Classification of the headache

In the first of a new series of monthly headache fact files in association with the RCGP, headache lead Dr David Kernick explains how headaches can be classified as primary and secondary.

Subarachnoid haemorrhage, as shown on CT scan, may present with thunderclap headache
Subarachnoid haemorrhage, as shown on CT scan, may present with thunderclap headache

Headache is formally classified by the International Headache Society.1 As the brain has no sensory fibres, intracranial pain arises from invasion, stretching, pressure on or inflammation of the meninges. Headaches can be classified as primary and secondary.

Primary headache
Primary headaches account for 90 per cent of presentations in primary care. There is no demonstrable underlying cause.


  • 85 per cent of GP headache presentations are migraines.
  • Severe episodic pain with or without aura and associated with nausea, photophobia and phonophobia.
  • Five per cent of these patients have chronic migraine, experiencing >15 days of migraine each month.

Tension-type headache:

  • Ten per cent of GP presentations but high population prevalence.
  • Poorly understood.
  • Dull, pressing pain usually bilateral with no nausea, photophobia or phonophobia.
  • Episodic or chronic.

Cluster headache and autonomic cephalalgias:

  • Cluster headache and other autonomic cephalalgias account for less than 1 per cent of GP headache presentations.
  • Patients experience very severe unilateral pain with autonomic features rarely with nausea, photophobia or phonophobia.

Secondary headache

In these headaches an underlying cause is demonstrable.

Subarachnoid haemorrhage:

  • Characterised by thunderclap headache - worst headache ever rising to a maximum within a minute.
  • Ten per cent of thunderclap headaches are due to subarachnoid haemorrhage.
  • Medical emergency with high mortality.
  • Sentinel headaches may be recognised in retrospect.

Temporal arteritis:

  • Occurs over the age of 50.
  • Forty per cent will have polymyalgia rheumatica.
  • Can be systemically unwell.
  • May have jaw claudication.
  • Raised ESR or CRP in 97 per cent of cases.
  • Temporal artery biopsy may confirm diagnosis.


  • Apart from malignant hypertension, the contri-bution of hypertension to headache is overrated and in practice is negligible.

Carotid/vertebral artery dissection:

  • Pain can radiate anywhere in face and neck.
  • May occur after trauma.
  • Collagen disease is a risk factor.


  • Non-specific headache can be associated with stroke.


  • Headache is common during course of illness, but only 10 per cent of tumours present with isolated headache.

Idiopathic intracranial hypertension:

  • Common in young obese women.
  • Headache and papilloedema often with pulsatile tinnitus.
  • Can lead to permanent loss of vision.
  • Refer.

Intracranial hypotension:

  • Intracranial hypotension occurs due to cerebrospinal fluid volume depletion as a result of leakage.
  • Headache is worse on standing and alleviated by lying down.
  • Classically post lumbar puncture but spontaneous leaks can occur.
  • Refer.

Headache attributed to trauma:

  • Can occur up to seven days post trauma.
  • Intensity of pain may not be related to degree of trauma.
  • Most resolve in less than six months but 25 per cent can go on for longer.
  • Watch for development of depression.
  • Headache can be part of a post-concussive syndrome associated with other non-specific symptoms.

Referred headache:

  • Cervicogenic pain is most common but is overrated as cause of headache.
  • Eyes, tempero-mandibular joint, teeth and sinus (85 per cent of diagnosed chronic sinusitis is migraine) are all possible but overestimated as causes of headache.

Activity-associated headache
During sexual activity the patient may experience a dull headache that increases with sexual activity or a sudden severe headache at orgasm.

The latter needs investigation.

Exercise-induced headache may be a co-existing primary headache induced by exertion. Underlying pathology must be excluded.

Treatment of both is pre- emptive (indometacin) or preventative (beta blocker).

Other causes
Obstructive sleep apnoea may be due to CO2 retention or poor sleep. It is reversible with treatment of the cause.

Renal failure, thyroid disease and raised calcium can also cause headache. Carbon monoxide poisoning may cause headaches and fatalities. Alcohol and drugs can be a cause.

Meningitis, encephalitis, TB or a systematic infection may cause headache.

Medication overuse headache affects up to 3 per cent of the population. It can occur with regular analgesia or triptan use. All analgesics and NSAIDs are implicated, particularly codeine compounds.

Cranial neuralgias

  • Trigeminal neuralgia is most common.
  • Burning or stabbing pain lasting less than two minutes, often provoked by mild pressure or triggers. Vascular compression of a nerve is the most common cause.
  • Trigeminal neuralgia may be confused with idiopathic stabbing headache, particularly with co-existing migraine.

Dr Kernick is a GP in Exeter and RCGP headache lead

For videos on headache investigation, see www.rcgp.org.uk/circ

1. The Headache Classification Subcommittee of the International Headache Society. The International classification of headache disorders, 2nd ed. Cephalgia 2004; 24 (suppl 1): 1-160

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