Unilateral Headache: what causes pain that only ever appears on one side of the head?

Unilateral Headache means that the pain only ever occurs on one side of the head, and never shifts to the other. About one in five people with migraine will experienced "side-locked" pains in the head.

However, a one-sided headache, which never moves, can suggest an underlying structural problem, not just simple migraine or tension-type headache.

By far the most common cause of unilateral headache is pain coming from the neck - called cervicogenic headache. Fortunately cervicogenic headache can usually be treated by physical therapy, or a course of painkillers.

Here's the list of causes of "side-locked headache" - pain only ever on one side of the head:

Picture of harlequin mask - one side remains different from the other
  1. Cervicogenic Headache
  2. Cluster Headache
  3. Paroxysmal Hemicrania
  4. Hemicrania Continua

Hemicrania Continua (HC) is one of the treatable causes of persistent daily unilateral headache.

It should always be considered when dealing with someone who complains of a high level of pain, and that pain is located one one side of the head and only on that side of the head.

The moderate-severe headaches can appear in episodes lasting for weeks at a time.

These episodes - relapsing-remitting-type- occur in about 15% of HC cases.

Relapsing-remitting pains can then develop into a more persistent daily headache - which is the case in 32% of cases.

The remainder (>50%) have an unremitting type of unilateral headache.

Associated with this headache are migrainous symptoms such as photophobia, nausea or phonophobia. Autonomic features like small pupils (meiosis), lacrimination (watering eye) can occur.

Jabs and jolts of pain - ice-pick type pains are also quite common.

Why is Hemicrania Continua an important diagnosis?

The main reason is that this is one of the indomethacin responsive headaches.

Hemicrania can be mistaken for tension-type headache or even migraine or cluster headache.

However if indomethacin is not administered, the patient will continue to experience headache (unless they are one of the 15% with remitting symptoms).

HC can occur post-partum and is one of the causes of headache during or after pregnancy.

There are single case reports of HC associated with the following conditions.

  1. Meningioma of the sphenoid bone
  2. HIV infection
  3. Lung Adenocarcinoma
  4. Carotid dissection

Most cases are without a known cause, and functional MRI studies suggest that there is abnormal activation of the posterior hypothalamus and dorsal - rostral pons.

Patients diagnosed with HC should have brain imaging studies to exclude skull base meningioma and carotid dissection should be considered.

Indomethacin should be given if Hemicrania is considered as a diagnosis.

Usually doses of between 75mg and 225mg daily are needed, and about a quarter of people on this drug will have heartburn which can be relieved by Ranitidine or a Proton-Pump-Inhibitor drug like Lansoprazole.

After treatment for 3 months, indomethacin could be withdrawn to see if remission has occurred.

Melatonin has also been used to treat some cases of HC.

  1. SUNCT
  2. Trigeminal Neuralgia
  3. Supraorbital Neuralgia
  4. Occipital Neuralgia (more correctly called Cervicogenic Headache)
  5. Temporal Arteritis
  6. Carotid Dissection
  7. Vertebral Dissection
  8. Nervus Intermedius neuralgia (usually ear pain, not headache

About 20% of people who get migraine will experience pain exclusively on one side of the head.

If you do not have migraine and experience strictly one-sided headaches, a search for an underlying structural problem within the head, with CT Brain scan or MRI scan is indicated, unless there is clear evidence that you have a neck problem (a history of previous trauma to the neck or restricted neck movements).

The regions of interest for the brain scan are either side of the pituitary gland (the parasellar structures, like the cavernous sinus), and the hypothalamus and pituitary itself.

This is particularly true if your headache has reddening of the eye (conjunctival injection), eye watering (lacrimation), nasal blockage or eyelid drooping (ptosis) associated with it - the so called autonomic features.


If there are no references listed, please notify me, as this box should contain a list of information sources, or a link to a 'Systematic Review' of the topic discussed on this page.

Espada et al Hemicrania Continua - 9 new cases. Cephalalgia 1999;19:442 (Free Abstract Only)

Peres MF et al. HC is not that rare. Neurology 2001;57;948-51 (Free Abstract Only)

Rozen TD. Melatonin as treatment for indomethacin-responsive headache syndromes. Cephalalgia 2003; 23: 734–5. (Free Abstract Only)

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