Migraine is probably best thought of as not one, two, or three illnesses, but several, even a multitude. Although characteristic types of headache attacks have been exceedingly well documented, we still do not know enough of life histories of individuals to categorize most disease entities, eg, common migraine or muscle contraction headache, as opposed to describing individual attacks.
Certainly the prevalence of the headache symptom is great and may well have been so since the evolution of man. Headache attacks have been described since ancient times, and their frequent unilateral nature gave rise to the term hemicrania, which eventually evolved into migraine. Wherever, in modern times, populations have been systematically studied, varying but usually large, percentages have been found to be subject to some degree of headache, although such systematic studies have not been many. Whether the prevalence of the symptom, in any or all of its forms, is similar