CENTRAL REPRESENTATION OF PHANTOM LIMB PHENOMENON IN AMPUTEES STUDIEDWITH SINGLE-PHOTON EMISSION COMPUTERIZED-TOMOGRAPHY

To explore the possible mechanisms of phantom limb discomfort after am putation, three amputees with phantom limb pain were studied. This stu dy examined the change of regional cerebral blood flow using technetiu m-99m hexamethylpropyleneamine oxime-single photon emission computeriz ed tomography, which was arranged at the time of severe phantom limb d iscomfort and after the discomfort subsided or was completely relieved . Nine representative transverse slices parallel to the orbitomeatal l ine were selected for quantification. The cortical ribbon (2-cm thickn ess) was equally subdivided into 12 symmetrical pairs of sector region s of interest in each slice. The irregularly shaped regions of interes t were drawn manually around the right thalamus and basal ganglion and then mirrored to the left thalamus and basal ganglion. The contralate ral to ipsilateral ratio of regional cerebral blood flow for each area was calculated. The intensity of phantom limb pain was evaluated on a 0 to 10 visual analog scale. In Cases 1 and 2, the contralateral to i psilateral regional cerebral blood flow ratios of multiple areas of th e frontal, temporal, or parietal lobes were increased at the time of m ore severe phantom limb pain, and the ratios were normalized or even d ecreased when the phantom limb pain subsided. In Case 3, increased con tralateral to ipsilateral regional cerebral blood flow ratios were als o found over the frontal, temporal, and parietal lobe. However, most o f the increased regional cerebral blood flow ratios of regions of inte rest in the first study persisted in the follow-up study. Also, the re gional cerebral blood flow ratios of greater number of regions of inte rest of the same gyrus and new gyrus were Increased. There was no sign ificant right-left difference of regional cerebral blood flow over bil ateral thalami and basal ganglia in all three cases. The results sugge sted that phantom limb pain might be associated with cortical activati on involving the frontal, temporal, or parietal cortex, and it may imp ly the possibility of the existence of an ascending polysynaptic pathw ay that conveys the uncomfortable phantom limb sensation to the cerebr al cortex. These findings may also indicate that reorganization of the cortical blood flow occurs in amputees. However, it is still difficul t to conclude that the changes in regional cerebral blood flow were at tributable directly to pain. With no comparison group of amputees and because of the small number of cases, it is hard to generalize about c erebrocortical involvement in phantom pain, and it is possible that th e findings represent a normal phenomenon seen after amputation. Anothe r possibility is that the findings represent increased arousal caused by pain rather than an intrinsic pain pathway. Further study is worthw hile.