ALTERATION OF CENTRAL EXCITATION CIRCUITS IN CHRONIC HEADACHE AND ANALGESIC MISUSE

Central excitatory circuits could be involved in the pathophysiology o f pain; particularly, the genesis of chronic pain. The ''second pain'' is the sensation that follows the initial pain after an appropriate n ociceptive stimulus. The second pain is amplified by repeating the sti mulus after brief intervals (temporal summation). This phenomenon is t he psychophysical correlate of the excitatory pain circuits. The tempo ral summation of the second pain was evaluated in four groups of subje cts: one group affected by migraine without aura, one by episodic tens ion headache, one by chronic daily headache, and a group of healthy su bjects. A percutaneous electrical shock was used as the nociceptive st imulus. The intensity of the second pain was significantly greater in the group of patients with chronic headache in comparison with the oth er groups. The patients with chronic headache were subdivided into thr ee groups on the basis of their clinical history: a group with transfo rmed migraine; a group with chronic headache ab initio, a form related to the first one; (both groups suffered from chronic daily headache w ith a frequent superimposition of episodes of migraine attacks) and th e third group consisted of patients with chronic tension headache. The temporal summation of the second pain was altered in the first two gr oups. The patients with chronic migraine abused ergotamine given as a symptomatic drug. Those who were able to discontinue this drug were re tested and reported a decrease of the second pain in comparison to the previous measurements. The results of the present study indicate that central excitatory circuits could be involved in the mechanism leadin g to the development of chronic daily headache.