ANATOMY AND PHYSIOLOGY OF HEADACHE
Headache is one of the most common symptoms evaluated by neurologists and bears a vast differential diagnosis. The successful management of both primary and secondary headache disorders requires an understanding of the relevant neuroanatomy and underlying physiology.
Pain typically occurs when peripheral nociceptors are stimulated in response to factors such as tissue injury or visceral distension. In this setting, pain perception is a normal physiologic response mediated by a healthy nervous system. However, pain can also occur from damage or inappropriate activation of pain-producing pathways of the peripheral or central nervous system. Headache may result from either or both of these mechanisms. There are relatively few pain-generating cranial structures, which include the scalp, falx cerebri, dural sinuses, and proximal segments of the large pial arteries. The majority of the brain parenchyma, ventricular ependyma, choroid plexus, and pial veins are not thought to be capable of producing pain.
The key structures involved in primary headache appear to be the following:
the large intracranial vessels, dura mater, and the peripheral terminals of the trigeminal nerve that innervate these structures
the caudal portion of the trigeminal nucleus, which extends into the dorsal horns of the upper cervical spinal cord and receives input from the first and second cervical nerve roots (the trigeminocervical complex)
rostral pain-processing regions, such as the ventroposteromedial thalamus and the cortex
pain modulatory systems in the brain that modulate input from trigeminal nociceptors at all levels of the pain-processing pathways and influence vegetative functions, such as hypothalamus and brain stem structures
The innervation of the large intracranial vessels and dura mater by the trigeminal nerve is referred to as the trigeminovascular system. Cranial autonomic symptoms, such as lacrimation, conjunctival injection, nasal congestion, rhinorrhea, periorbital swelling, aural fullness, and ptosis, are prominent in the trigeminal autonomic cephalalgias (TACs) and may also be seen in migraine. Such autonomic symptoms result from activation of cranial parasympathetic pathways; functional imaging studies also suggest that vascular changes in migraine and cluster headache, when present, are similarly driven by these cranial autonomic systems. These symptoms can often be mistaken for signs of sinus inflammation, frequently resulting in inappropriate management. Migraine and other primary headache syndromes are not primarily “vascular headaches” as was once thought; these disorders do not reliably demonstrate vascular changes, and treatment outcomes cannot be predicted by vascular effects. Migraine is fundamentally a brain disorder and should be understood and treated as such.
CLINICAL EVALUATION OF HEADACHE DISORDERS
The differential diagnosis of a new, severe headache is quite different from a chronic, recurrent headache. There is a greater likelihood of finding a potentially serious cause with new-onset and severe headache than with recurrent headache over years. Lifethreatening headache is relatively uncommon, but vigilance is required in order to recognize and appropriately treat such patients. Serious causes to be considered include meningitis, subarachnoid hemorrhage, epidural or subdural hematoma, glaucoma, tumor, and purulent sinusitis. The approach to the patient presenting with severe, new-onset headache is also discussed in Chapter 7.
A classification system for headache disorders has been established by the International Headache Society (IHS)—the International Classification of Headache Disorders, now in its third edition. The most recent version divides headache disorders into primary syndromes (in which the headache and associated features constitute the disorder itself) and secondary disorders (in which the headache results from exogenous causes).
SECONDARY HEADACHE
Concerning underlying conditions that are associated with headache are described in the following text and detailed further in Chapter 7; however, it should be noted that the vast majority of patients presenting with severe headache have a benign cause. The management of secondary headache focuses on diagnosis and treatment of the underlying cause.
Meningitis: Acute, severe headache with fever and stiff neck suggests meningitis (see
Chapter 61). Often, there is significant worsening of pain with eye movement. Lumbar puncture is necessary for diagnosis. Meningitis can be easily mistaken for migraine in that the cardinal symptoms of pounding headache, photophobia, nausea, and vomiting are frequently present, perhaps reflecting the underlying physiology in some of these cases.
Subarachnoid hemorrhage: Acute, severe headache with stiff neck but without fever suggests subarachnoid hemorrhage (see
Chapter 39). A ruptured aneurysm, arteriovenous malformation, or intraparenchymal hemorrhage may also present with headache alone. In rare cases (particularly if the hemorrhage is small or below the foramen magnum), head computed tomography (CT) can be normal. Thus, lumbar puncture may be required for definitive diagnosis of a subarachnoid hemorrhage.
Brain tumor: Brain tumor is a rare cause of headache and even less commonly a cause of severe pain. The head pain is generally nondescript—an intermittent deep, dull ache of moderate intensity, which may worsen with exertion or change in position and may be associated with nausea and vomiting. Such symptoms are caused by migraine far more often than from brain tumor. The headache of brain tumor awakens patients from sleep in about 10% of cases. Vomiting that precedes the development of headache by weeks is highly characteristic of posterior fossa brain tumors. Head pain triggered by Valsalva maneuvers such as bending, lifting, or coughing can be due to a posterior fossa mass. De novo headache in a patient with known malignancy may suggest cerebral metastases and/or carcinomatous meningitis.
Temporal arteritis: Temporal (giant cell) arteritis is an inflammatory disorder of arteries that frequently involves the extracranial carotid circulation. The average age of onset is 70 years, and women account for 65% of cases. About half of patients with untreated temporal arteritis develop blindness due to involvement of the ophthalmic artery and its branches. Because treatment with glucocorticoids is effective in preventing this complication, prompt recognition of the disorder is important. Headache is the dominant symptom and often appears in association with malaise and myalgias. Head pain may be unilateral or bilateral and is located temporally in 50% of patients but may involve any and all aspects of the cranium. The quality is almost always described as dull and boring, with superimposed episodic stabbing pains and exquisite scalp tenderness. Patients often describe a superficial origin of their headache (external to the skull, rather than originating deep within the head as in migraine). Headache is usually worse at night and often aggravated by exposure to cold. Additional findings may include reddened, tender nodules or red streaking of the skin overlying the temporal arteries and tenderness of the temporal or, less commonly, the occipital arteries. The management of temporal arteritis is further discussed in Chapters 7 and 42.
Glaucoma: Glaucoma may present with a prostrating headache associated with nausea and vomiting. The headache often starts with severe eye pain. On physical examination, the eye is often red with a fixed, moderately dilated pupil.
PRIMARY HEADACHE SYNDROMES
Primary headache syndromes are disorders in which the headache and associated features occur in the absence of exogenous etiologies. The most common are migraine, tension-type headache, and the TACs, notably cluster headache; the complete list is in
Table 54.1.
MIGRAINE
EPIDEMIOLOGY
Migraine is the second most common cause of headache and ranks among the top 20 causes of disability worldwide by the World Health Organization. It afflicts approximately 12% of the population annually (15% of women and 6% of men over a 1-year period). Migraine is a recurring syndrome of head pain along with symptoms of neurologic dysfunction, such as sensitivity to sensory stimuli (light, sound, smell, or movement); nausea and vomiting often accompany the headache.
The migraine brain is particularly sensitive to environmental and sensory stimuli; migraine-prone patients do not habituate easily to sensory input. Headache can be initiated or amplified by various triggers, including bright lights, sounds, smells, or other afferent stimulation; hunger; stress or the let down from stress; physical exertion; stormy weather, altitude, or barometric pressure changes; hormonal fluctuations during menses; lack of or excess sleep; and alcohol or other chemicals, such as nitrates. Identifying a patient’s susceptibility to specific triggers can be useful in advising lifestyle adjustments as part of the treatment plan.
DIAGNOSIS AND CLINICAL FEATURES
Diagnostic criteria for migraine headache are summarized in
Table 54.2. Migraine has several forms that have been defined: migraine with and without aura, episodic migraine, and chronic migraine (see
Table 54.1). The migraine aura, such as the visual disturbances with flashing lights or zigzag lines moving across the visual field or other neurologic symptoms, is reported in only 20% to 25% of patients. Patients with episodes of migraine that occur on 15 or more days per month are considered to have chronic migraine. Most patients with disabling headache likely have migraine, as opposed to tension-type headache, which is the most common primary headache disorder (discussed later in this chapter).
Patients with acephalgic migraine (typical aura without headache, 1.2.1.2) experience recurrent neurologic symptoms, frequently with nausea or vomiting, but with little or no headache. Vertigo can be prominent; it has been estimated that one-third of
patients referred for vertigo or dizziness have a primary diagnosis of migraine. Migraine aura can have prominent brain stem symptoms (such as diplopia, ataxia, altered consciousness, dysarthria, tinnitus, and vertigo) and the terms
basilar artery and
basilar-type migraine have now been replaced by
migraine with brain stem aura (see
Table 54.1).
TREATMENT OF MIGRAINE
Once a diagnosis of migraine has been established, it is important to assess the extent of a patient’s disease and level of functional impairment. The Migraine Disability Assessment Score (MIDAS) is a well-validated, easy-to-use tool. A headache diary also helps assess disability as well as the frequency of abortive medication use. Patient education is an important aspect of migraine management. It is useful for patients to understand that migraine is an inherited vulnerability for head pain and associated neurologic symptoms and that although the disorder cannot be “cured,” migraine can be modified and managed by lifestyle adjustments and medications. Furthermore, patients should be reassured that migraine is generally not associated with serious or life-threatening illnesses.
Nonpharmacologic Management
Migraine can often be managed at least in part by a variety of nonpharmacologic approaches. Many benefit by identifying and avoiding specific headache triggers. A regulated lifestyle is important, including a healthy diet (with a regular eating schedule), exercise, routinized sleep patterns, avoidance of excess caffeine and alcohol, and minimizing acute changes in stress levels (such as through biofeedback, meditation, or yoga). Lifestyle modifications that are effective in reducing headache frequency should be maintained on a routine basis, as these provide a simple, costeffective approach to migraine management. If these measures fail to prevent an attack, abortive pharmacologic measures are then needed.
