HEADACHE IS A COMMON PATIENT COMPLAINT, both in the United States and globally. If persistent or severe, headaches can create a significant level of functional impairment. Both the general and subspecialized physiatrist will undoubtedly encounter headache as a part of their clinical practice. The goal of the chapter is to provide a brief overview of the characterization and management of common headache conditions.

Head pain by patient report was the fifth-leading cause of emergency department visits overall in the United States and accounted for 1.2% of outpatient visits, according to data from the National Hospital Ambulatory Medical Care Survey (2009) and National Ambulatory Medical Care Survey (2009), respectively.¹

Tension-type and migraine headaches are the most common causes of primary headache. Interestingly, systemic infection is the most common etiology of secondary headaches, with head injury being the second most common etiology (Table 39–1).

Headaches and migraines are more common in females than in males, as represented in several population-based studies. Additionally, migraines tend to be more common in the 25- to 55-year-old age group. The American Migraine Prevalence and Prevention study estimates a migraine prevalence of 11.7% in the United States using the International Classification of Headache Disorders (ICHD-2) criteria, with an additional 4.5% being classified as “probable migraine.” Severe headache and migraine combined prevalence ranges from 16.6% to 22.7% based on ongoing U.S. public health surveillance studies.¹ Data on tension-type headache prevalence is less readily available but is generally thought to be more prevalent than migraine. A review on the global burden of headache² reports that current adult prevalence for headache in general is 46%, 11% for migraines, and 42% for tension-type.

There are complex mechanisms of pain generation and pain processing for headache disorders. The basic principles involved in the generation of headache will be reviewed and will serve as a foundation for the management of headache disorders. With respect to headache, pain may be generated when nociceptors and pain pathways, which involve either the peripheral or central nervous system, are activated. Major pain-producing structures include the scalp, dural sinuses, meningeal or pial arteries, and the falx cerebri. Of these, the large intracranial vessels, dura mater and trigeminal nerve/nucleus, seem to be most involved in the generation of primary headaches (Fig. 39–1).

Most of the research in this field has been focused on migraine headaches. Intracranially, the innervation surrounding the cerebral vessels, cerebral sinuses, and dura mater is well characterized. These pathways are thought to be composed of largely unmyelinated fibers that arise from the trigeminal ganglion (especially the ophthalmic division, V1) for supratentorial structures and the upper cervical dorsal roots in the posterior fossa (Fig. 39–2). This trigeminovascular nociceptive information is then relayed through the thalamus to cortical areas for processing. Sensitization of intracranial components results in the manifestation of extracranial pain symptoms. Such pain is often mediated by the trigeminal nerve or the second cervical nerve root (see Fig. 39–2).

There is a genetic predisposition for migraine headaches with evidence that migraine in a first-degree relative increases an individual’s risk. Familial hemiplegic migraine is a rare subtype of migraine with aura that has been linked to specific gene mutations, the most common of which is CACNA1A, which codes for a voltage gated neuronal channel. Another well-defined group of patients predisposed to develop migraine headaches with aura are those with the CADASIL mutation, a nonamyloid arteriopathy caused by mutations in the NOTCH3 gene.

In contrast, the pathophysiology of tension-type headache is not well understood. There may be a genetic predisposition for tension headaches but this has not been characterized. Although muscle contraction seems to be implied in the name “tension headache,” this feature is not a prerequisite for diagnosis.

The International Headache Society published the International Classification of Headache Disorders (ICHD), a hierarchical headache classification system for use in both research and clinical practice. The second edition of this classification system (ICHD-2) was published in 2004 and has been widely used, and a beta version of a third edition (ICHD-3, beta) was published in 2013 (Table 39–2).

The classification of headaches is divided into two main categories: primary headache and secondary headache. The third general category, including facial pain, is addressed in a subsequent chapter in this textbook. In clinical practice these guidelines serve as a detailed resource of diagnostic criteria by which a practitioner can confidently arrive at an appropriate clinical headache diagnosis for even the most nuanced of cases. We will use this guideline here to define the clinical criteria of the major headache diagnoses to be discussed.

With regard to primary headache disorders, there are two major types: migraine headache and tension-type headache. Tension-type headaches are by far the most common. Also included in primary headaches are trigeminal autonomic cephalgias (e.g., cluster headache and paroxysmal hemicranias), as well as a myriad of “other” primary headache disorders such as cough headache, exercise headache, and headache associated with sexual activity, which are beyond the scope of this chapter.

A migraine without aura is defined as a recurrent (at least five attacks) headache disorder with each attack lasting between 4 and 72 hours (Table 39–3).

The headache must display at least two of the following characteristics: unilateral location, pulsating quality, moderate or severe pain intensity, and aggravation by routine physical activity. Additionally, the headache must be associated with nausea, vomiting, photophobia, or phonophobia (Table 39–4). There are specific descriptions in the guidelines of what would constitute aura (preceding visual, sensory, speech, or motor symptoms); the reader is directed to the guidelines for more details in this regard. To meet criteria for chronic migraine, a patient must have 15 or more headache days per month for at least 3 months; however, only 8 of those headache days are required to meet criteria for migraine (the remainder of the headaches may meet criteria for tension-type headache).

Tension-type headaches are a recurrent (at least 10 episodes) headache disorder with several phenotypic differences from migraine. The tension-type headache can last hours to days or even be unremitting. In contrast to migraine headaches, tension-type headaches must display two of the following characteristics: bilateral location, pressing/tightening quality of pain, pain that is mild to moderate in intensity, and no aggravation by routine physical activity. Additionally, the headaches should not be associated with more than one episode of mild nausea, photophobia, or phonophobia. With regard to frequency, less than 1 headache day per month is considered infrequent, 1 to 14 days per month is considered frequent, and chronic is defined as greater than or equal to 15 days per month for at least 3 months (Fig. 39–3).