A LONGITUDINAL-STUDY OF SOMATESTHETIC PERCEPTUAL DISORDERS IN AN INDIVIDUAL WITH A UNILATERAL THALAMIC LESION

Several aspects of tactile, thermal and pain perception were evaluated in an individual (R.S.) with a hemorrhagic lesion centered in her lef t lateral thalamus. Over a 4-year period, psychophysical evaluations w ere undertaken every 6-8 months, and five magnetic resonance (MR) stud ies were conducted. Early tests (1991-1992) revealed large contralater al deficits in R.S.'s perception of touch, innocuous temperature, and mechanically evoked cutaneous pain -more so for the upper versus the l ower extremity. R.S. showed a similar pattern for heat pain sensitivit y, but a more modest deficit than for mechanically evoked pain. She sh owed a deficit for cold pain sensitivity on her foot, but not for her hand. Thresholds for all types of stimuli ipsilateral to the lesion we re within a normative range. Late in 1993, R.S. demonstrated improveme nts in sensory capacity for touch and mechanically evoked pain contral aterally, although deficits were still evident. During the same period , heat pain sensitivity improved contralaterally, and strikingly, a pe rmanent, ipsilateral hypersensitivity to heat pain developed in her ha nd. Throughout the entire testing period, R.S.'s ratings of perceived unpleasantness matched the patterns of perceived pain intensity. Thus, the discriminative and the affective dimensions of her pain would cha nge in tandem. However, perceptible innocuous thermal stimuli evoked n o affective response when applied contralaterally, despite being descr ibed as pleasant when presented ipsilaterally. Throughout the testing period, R.S. reported a persistent numbness on her right hemi-body. On ly during a 3-month period in 1995 did she experience spontaneous pain , which was referred to her right foot. The only change in psychophysi cal performance related to her right foot was a transient but intense thermal allodynia several months prior to her spontaneous pain. The MR studies over this 4-year period showed changes in the extent of edema , gliosis and/or ischemia that could be related to perceptual changes. Thus, the conspicuous observations in this thalamic lesion case were: (i) differential effects upon the various pain modalities (mechanical , heat and cold); (ii) development of thermal allodynia without mechan ical allodynia, including an ipsilateral effect; (iii) a deficit in po sitive affective responses to temperature; and (iv) the different time courses for changes in evoked somesthetic capacity versus spontaneous paresthesias and pathological pain. (C) 1997 International Associatio n for the Study of Pain. Published by Elsevier Science B.V.