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Classical clinical teaching, familiar to practically all doctors and drummed into all medical students, is that one of the features of raised intracranial pressure (ICP) is headache which causes nocturnal or early morning waking, and/or is worse on waking, then declining in severity after getting up. This nocturnal or early morning headache is thought to reflect exacerbation of raised ICP through recumbency, nocturnal hypoventilation with a rise in PaCO 2 and cerebral vasodilatation, 1 and possibly increased brain metabolism during REM (rapid eye movement) sleep. 2 Such headaches are almost invariably associated with papilloedema, and sometimes with vomiting which may lead to hyperventilation and reduction of ICP. In the UK, headache with vomiting and papilloedema is enshrined in Department of Health guidelines for urgent evaluation (the "two-week rule"), although in practice very few patients referred under these guidelines have such features, or indeed cerebral tumours. 3 In fact, any patient with all three features should be seen immediately, certainly not wait for even two weeks, because they may very well have raised ICP.
So, are all morning headaches due to brain tumours with raised ICP? Clearly not, but neurologists are often referred patients with a history of nocturnal and/or awakening headaches-"query raised ICP", in the apparent absence of other neurological symptoms and signs. The differential diagnosis is in fact quite broad (see box), encompassing not only intracranial hypertension but also a number of primary and secondary headache disorders, as well as general neurological, medical and psychiatric conditions.
Differential diagnosis of nocturnal and/or awakening headaches
Raised intracranial pressure
Neoplasm
Intracranial hypertension secondary to hydrocephalus
Primary headache disorders
Migraine
Trigeminal autonomic cephalalgias
Cluster headache
Paroxysmal hemicrania
Short-lasting unilateral neuralgiform headache attacks with conjunctival
injection and tearing (SUNCT)
Hemicrania continua
Hypnic headache
Primary headache associated with sexual activity
Secondary headache disorders
Medication-overuse headache
Hangover headache
Giant cell (temporal) arteritis
Sphenoid sinusitis
Carbon monoxide-induced headache
Subarachnoid haemorrhage
Other disorders
Headache attributed to epileptic seizure
Sleep apnoea hypopnoea headache
Depression
Exploding head syndrome
PRIMARY HEADACHE DISORDERS
Migraine
There is a circadian variation in migraine onset, with preferential (but not exclusive) onset in the night or early morning, between 04:00 h and 09:00 h. 4 There is an older literature devoted to "nocturnal migraine" and "early morning migraine", although there...