TONIC PAIN - A SPET STUDY IN NORMAL SUBJECTS AND CLUSTER HEADACHE PATIENTS

Whether the pathogenesis of cluster headache (CH) is peripheral or cen tral is still matter of debate. An involvement of central structures r elated to pain perception and modulation, which also causes an alterat ion of the physiological pattern of pain perception in CH, has been hy pothesized. We investigated the pattern of brain response to pain in n ormal subjects and CH patients by evaluating the cerebral blood flow ( CBF) changes using an experimental model of tonic aching pain stimulat ion, the cold water presser test (CWPT). CBF was assessed quantitative ly by the Xe-133 inhalation method and single photon emission tomograp hy (SPET), at rest and during CWPT, as previously described (Di Piero et al., 1994). CWPT was performed in 12 volunteers and in seven patien ts with CH. All the CH patients had a left-sided headache and were stu died in a headache-free phase out of the cluster period. During CWPT, volunteers showed a significant CBF increase in the contralateral prim ary sensorimotor (P < 0.001), frontal (P < 0.01) and temporal (P < 0.0 02) regions and thalamus (P < 0.01) and in the ipsilateral temporal (P < 0.005) and anterior cingulate (P < 0.01) regions. During left-hand stimulation (ipsilateral to the headache side) by CWPT in CH patients, CBF changes were significantly lower than those observed in volunteer s in the contralateral primary sensorimotor region (P < 0.0005) and th alamus region (P < 0.01). Then were no significant differences in the brain response observed during the stimulation of the hand contralater al to the headache side. In conclusion, in a headache-free phase out o f the cluster period, the pattern of cerebral activation during tonic pain stimulation of the hand ipsilateral to the headache side is criti cally modified in CH patients in areas which are probably involved in the detection of the stimulus intensity. This modification may reflect a marker of a biological modification of the pain conveyance system. The fact that it is also present out of the active period of the disea se, suggests a possible involvement of central tonic pain mechanisms i n the pathogenesis of CH. (C) 1997 International Association for the S tudy of Pain.