Headache
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Evidence has accumulated in recent years indicating structural, physiologic, and biochemical alterations in the brain of patients with chronic migraine (CM). Altered pharmacologic responses to opioids and other analgesics have also been reported. Structural or morphologic changes include reduced cortical gray matter of the pain processing areas of the brain and iron accumulation in the periaqueductal gray matter (PAG), red nucleus, and basal ganglia structures. ⋯ Suppression of cortical spreading depression by these agents is correlated with the dosages and the duration of treatment. The beneficial effect of botulinum toxin in CM may be due to its antinociceptive effect. Changes in the glutamate and calcitonin gene-related peptide at the peripheral nerve endings reduce peripheral sensitization, which eventually leads to reduced central sensitization.