Migraine Mimics
This section comprises two distinct groups:
Primary headache conditions classified as separate entities, such as the trigeminal autonomic cephalgias which are distinguished by differences in their postulated pathophysiology and treatment recommendations.
Secondary or symptomatic migraine, much less common than primary migraine, but important to differentiate because of their underlying causes.
Trigeminal Autonomic Cephalgias
The trigeminal autonomic cephalgias are a group of primary headache disorders characterised by autonomic features in conjunction with unilateral headache. The group includes cluster headaches, paroxysmal hemicranias, hemicrania continua and 'short-lasting, unilateral, neuralgiform headache attacks with conjunctival tearing' (SUNCT). Cluster headache is the most common of these, differing from migraine in the boring quality of pain, often nocturnal and usually orbital, lasting 45–90 min, with prominent autonomic features, and a desire to walk around rather than sit still. The clinical features and treatments of trigeminal autonomic cephalgias are described elsewhere. There are distinct pathophysiology and treatment paradigms postulated for trigeminal autonomic cephalgias. Although these entities are presented as distinct syndromes, in clinical practice, many patients with cluster headache have migrainous features. Some patients have attacks with the cardinal features of cluster headache, but also have a few migrainous symptoms, especially a visual aura. A recent study found 24.5% of patients with cluster headache had at least one migrainous feature. The term 'cluster migraine' is used to denote syndromes when there is significant overlap between cluster headache and migraine. Experienced neurologists see changing patterns occurring in some patients, who may have migraine with aura, migraine without aura, cluster headache and cluster migraine at different times in their lives. Response to treatment is also not exclusive: for example, migraine and other primary headache may respond to high-flow oxygen therapy as cluster headache does, and cluster headaches may respond to medications used for migraine, such as pizotifen and propranolol.
While striving for diagnostic clarity and avoiding unfocussed thinking, it is sensible to keep an open mind to the rich permeations encountered in presentations and responses to treatment of primary headache. Some patients have headaches that move from one phenotype to another (in the current headache classification). In the future, other biological markers may help with better understanding of the overlapping or changing phenotypes of primary headache in individual patients, and to modifications in our current classification.
Arterial Hypertension
It may be difficult to know whether headaches occurring with newly recognised hypertension are solely due to the hypertension, or represent a triggering of a tendency to migraine. Either way, new migraine or worsening migraine should always prompt checking of blood pressure.
Acute Glaucoma
Severe headache, with pain centred on one eye (sometimes with tenderness and hardness of the eye), with blurred vision or visual loss, with haloes around objects, or with redness of the eye, may each indicate acute closed-angle glaucoma, and is an emergency.
Carotid Artery Dissection
The headache of carotid artery dissection is variable. Most commonly it is distinguishable from migraine by being dull and without throbbing; however, it may be more migrainous, and even with a reported classical visual aura. As headache may precede ischaemic manifestations, it is important to consider the diagnosis, and look for ipsilateral neck pain, along with Horner's syndrome (40% of cases). Although Horner's syndrome is non-specific, it should prompt investigation of possible carotid artery dissection at its first presentation.
Structural Intracranial Lesions With or Without Raised Intracranial Pressure
Raised intracranial pressure or mass lesions may present with headache alone. This may be either chronic daily or subacute daily headache, and may have migrainous features; characteristically, however, there is an early morning preponderance, vomiting without nausea, visual obscurations, and later, clinical signs of reduced alertness, cranial nerves palsies—including sixth nerve palsy—and papilloedema.
Acute and Chronic Meningitis
Acute meningitis is usually apparent from the accompanying fever, neck stiffness and other neurological features. Chronic meningeal infection, inflammation and malignant meningitis usually have other symptoms and signs.
Giant Cell (Temporal) Arteritis
The characteristic headache of giant cell arteritis is throbbing, and the headache may be migrainous; but the associated features of scalp tenderness, jaw claudication, weight loss, fatigue and myalgia, in a person over 60 years of age, are important indicators of the diagnosis; any clinical suspicion should prompt urgent investigation.
Reversible Cerebral Vasospastic Syndrome
This entity is now defined as severe headache—with or without additional neurological symptoms—associated with vasospasm on cerebral angiography. The headaches are usually thunderclap. There is an underlying cause in about two-thirds of cases (post partum, hypertension, drugs), with the remainder having no known cause. Early descriptions emphasised its link with migraine, with headache indistinguishable from migraine and a good prognosis. Vasospasm in migraine does occur, and angiography can trigger migrainous infarction. However, in one series persistent focal cerebral events occurred at similar rates in patients with migraine compared to non-age-matched patients having angiography for other reasons (2.6% compared to 2.8%), although migraineurs had a 5% rate of transient deficits. As angiography is not usually carried out for acute uncomplicated migraine, the incidence of vasospasm is unknown.