Redefining primary headaches.

In the light of the pathophysiologic knowledge acquired in the recent years, a tentative redefinition is now possible of some types of headache until now defined as idiopathic, and indistinctly described as primary headaches. Cluster headache and trigeminal neuralgia are known examples of diseases classified as primary, which are, in contrast, well-defined diseases to be distinguished from headaches without any recognized anatomic site of lesion or pathogenesis. Another still debated condition, chronic migraine, is proposed here as the consequence of "processes" to be ascribed to mechanisms activated by other comorbid conditions. The observations supporting the possibility that allodynia represents the implicit process leading to pain progression, which occurs in some migraineurs, are discussed.