Clinical aspects of headache disorders
Headache affects more than 45 million individuals in the USA, which makes it one of the most common nervous system disorders (National Institute of Neurological Disorders and Stroke, 2002). The International Headache Society’s diagnostic criteria for headache disorders (ICHD-II, Headache Classification Committee, 2004) classifies primary headache disorders as those in which headache itself is the illness, with no other etiology diagnosed. Examples include migraine and tension-type headache (TTH). Headache disorders can be further classified as episodic (<15 headache days per month) or chronic (≥15 headache days per month for more than 3 months).
Migraine is a primary headache disorder characterized by enhanced sensitivity of the nervous system (Silberstein, 2000) associated with a combination of neurological, gastrointestinal and autonomic disturbances (Silberstein, 2004). The ICHD-II has provided criteria for a total of seven subtypes of migraine (including migraine with and migraine without aura). The ICHD-II diagnostic criteria for migraine without aura (Headache Classification Committee, 2004) include
headache associated with at least two of the following: unilateral location, pulsating quality, moderate or severe pain intensity and aggravation by or causing avoidance of routine physical activities
at least one of the following during headache: nausea and/or vomiting, photophobia and phonophobia
headache not attributable to another disorder.
It is estimated that 28 million Americans, including 18% of women and 7% of men, are afflicted with severe, disabling migraines (Lipton et al., 2001). The World Health Organization (2012) ranked migraine as one of the world’s most disabling illnesses, profoundly impacting quality of life and causing functional impairment and disruption of household or social activities. The economic burden of the disease to society is also considerable. In the USA, the yearly medical costs exceed 1 billion dollars, and costs to employers due to migraine-related absenteeism and reduced productivity is 13 billion dollars (Hu et al., 1999).