Neurobiology of chronicization.

In the past few years, research on chronicization of headache has focussed primarily on migraine, even though there are other types of primary headache that over time can turn into chronic forms. Only a minority of migraine sufferers will develop a chronic condition, with attacks that are likely to vary in their clinical features. As a result, in chronic migraine the specific diagnostic criteria for this headache type do not always exhibit the typical features of migraine. Among the factors that play a major role in favouring chronicization are a high frequency of migraine attacks since the beginning, overuse of symptomatic medication and onset of depression or arterial hypertension. Several neurophysiology, biochemistry and functional neuroimaging studies suggest that chronic migraine may be associated with structural, functional and metabolic changes in the brain, especially involving the brainstem.