We studied 18 patients with a single ischemic thalamic lesion, who had somatosensory disturbances and/or central
pain in the opposite hemibody, by correlating their clinical symptoms, somatosensory evoked potentials (SEPs), and computed tomography (CT) findings. Patients were divided into three groups: (1) those with somatosensory deficits, central
pain, and abnormal SEPs, which comprised two thirds of the patients (classic thalamic
pain syndrome), (2) those with somatosensory deficits, no central
pain, and abnormal SEPs (analgetic
thalamic syndrome), and (3) those with almost normal sense perception, central
pain, and normal SEPs (pure algetic
thalamic syndrome). CT evidence of a paramedian or anterolateral thalamic lesion might be an
indicator for the development of central
pain, because these types of
infarctions occurred only in patients with the classic
thalamic syndrome or the pure algetic
thalamic syndrome. The differentiation of the
thalamic syndrome into three subtypes is of prognostic value, because patients with a loss of cortical SEPs and a posterolateral ischemic thalamic lesion on the CT scan probably will not exhibit central
pain.