Excerpt from Pathophysiology and Treatment of Migraine and Related Headache

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Headache is a pervasive symptom and the most common problem neurologists encounter in their clinical practices. It affects an estimated 60-80% of Americans at any time. The history of headache can be traced almost to the beginning of the history of humankind. The first description of headache dates back to the third millennium BCE. Headache has been written about extensively since the time of the Babylonian civilization. Migraine headache and hemicrania are discussed in the Bible. Some famous historical figures (eg, Napoleon) are known to have had terrible headaches.

Much debate exists among headache specialists regarding the evolutionary mechanisms; however, all agree on the paucity of literature related to this topic. This lack most likely exists because headache is a subjective symptom, because no objective measures or standardizations are available, and because species studies are limited to humans. Two common evolutionary mechanisms of disease production have been described. The first is a protective mechanism in response to what the body perceives as an external environmental stress. The second, and simpler, mechanism is pathogen-mediated disease production (eg, disease due to infections caused by bacteria, viruses, or other pathogens). The first seems most likely to apply to headache.

Several observations give credence to the theory that the evolution of headache may be an internal protective response developed against environmental stressors. When exposed to extremes of temperature, humans can develop the classic vascular headache. The same is true for people who have had a sudden lack of sleep or food.

Common triggers of vascular headaches are stress, heat, or a lack of sleep or food. People with a predisposition to headache may have a lower threshold of response to these external stressors than other people. Patients with migraine may have inherited the predisposition for this lowered threshold. Therefore, some experts have theorized that headache is a slow, adaptive response. Most primary headaches develop slowly over minutes, if not hours. The pain associated with headache is transmitted by the slowest of all unmyelinated nerves.

For clinical purposes, the International Headache Society (IHS) (which revised the classification of headaches in 2004 [IHS-2]) divides headaches into 2 broad categories: primary headaches and secondary headaches. Primary headaches, which are headaches with no organic or structural etiology, include vascular (migraine) headache, trigeminal autonomic cephalalgias (which includes cluster headache), tension headache, and other secondary headaches (ie, hemicrania continua, new daily persistent headache, exertional headache, hypnic headache, thunderclap headache). Secondary headaches are those due to an underlying structural or organic disease and include 9 subcategories.

For excellent patient education resources, see eMedicine's Headache Center. In addition, visit eMedicine's patient education articles Causes and Treatments of Migraine and Related Headaches, Cluster Headache, Migraine Headache, Alternative and Complementary Approaches to Migraine and Cluster Headaches, Tension Headache, and Understanding Migraine and Cluster Headache Medications.

Please click here to view the full topic text: Pathophysiology and Treatment of Migraine and Related Headache