Heterogeneous Cerebral Blood Flow during Spontaneous Attacks of Migraine with and without Aura: A 99 mTc-HMPAO-SPECT Study

Modifications of Cerebral Blood Flow (CBF) during migraine attacks have been studied by several authors, using the Xenon 133 technique, sometimes with contradictory results : in common migraine particularly, the most of the authors noted a long-lasting and diffuse hyperemia However the Scandinavian group was unable to detect significant modification of CBF, suggesting that migraine attacks with and without aura have a different pathophysiology ; the mode of provocation of the attack (by drinking red wine) might explain their negative results in common migraine (I). PATIENTS : Eight patients (6 women, 2 men aged from 36 to 63 years) have been studied during the aura (scotoma) in one case and during the headache phase of a common migraine in the 7 other cases. The delay between the beginning of the headache and the CBF recording varied from 1 to 48 hours. A second CBF measurement was made several weeks later, at a distance of a migraine attack (minimum 6 days) ; thus each subject was his own control and we could compare the CBF modifications during the headache phase and in the pain-free period. METHOD : Fifteen mCi of 99 mTc-HMPAO (Amersham) were administered intravenously ; at the time of injection, patients were supine, motionless, eyes opened, in a silent room. Afterwards, symptomatic treatment for the acute attack of migraine was given if needed, on the assumption that the distribution of the tracer prior to treatment was fixed. SPECT data collection was carried out 15 to 45 min. post-injection using a rotating gamma camera (Gammatome 2, Sopha Medical). Sixteen slices (thickness 1 cm) parallel to orbitomeatal plane were achieved per study, and corrected images were obtained with normalization by the average count rate of the whole brain. "Pathological" regions were selected visually as those with the most pronounced side differrnces. The difference was calculated as the side difference divided by the "normal" side ("side to side asymmetry"in percent). Tracer activity was expressed as a ratio of the regional activity per pixel to the total activity of the whole brain (activity index). Normalization allowed us to compare 2 successive measurements in the same patient. RESULTS : In each subject, we found during the headache period, one or several areas of abnormal flow, presenting either as a hyperfixation of the tracer (5 times in 4 subjects), or as a hypofixation (9 times in 7 patients) (figure 1). The unique subject recorded during an aura (a scotoma in the left hemianoptic field) presented a 26 Yo hypofixation area in the right posterior parietal region. In migraines without aura, we found in 6 cases out of 7, zones of hypofixation between 11 and 21 % without any clinical correlation ("clinically silent oligemia areas"). Hyperfiation zones were less frequent and did not correlate with the side of the headache. Hypo and byperfuation foci could coexist during the same attack (patient number 2). In all subjects, these abnormalities tended to disappear after the migraine attack, but in some of them the asymmetry persisted at a lesser degree (figure 1). DISCUSSION : 99 mTc HMPAO-SPECT is a semi-quantitative method : regional tissue counts cannot be expressed in absolute units of flow and the images can be viewed only as relative distribution of rCBF. For this reason we only speak about hypo or hypesixation areas instead of hypo or hyperflows. Nevertheless we observed in all cases of common migraine, a very heterogeneous distribution of the tracer, which necessary implies CBF abnormalities. These abnormalities were more often areas of hypofixation, maybe because hyperflows are known to be underestimated by HMPAO technic. Our results are in complete disagreement with those of Costa et a1 (2) which, with the same method, found a normal CBF distribution in all four common migraine patients. On the other hand, Levine et a1 (3), using the 133Xe inhalation method, reported rCBF asymmetries during the headache-free period in 56% of patients with common migraine. In our