[Role of the lemniscal system in pain modulation--a consideration based on clinical experience]

Ten patients with intractable pain of central origin were operated on for pain relief by implanting the chronic stimulating electrode (Medtronic Co.) in the posterior limb of the internal capsule, thalamic sensory nuclei or mesencephalic lemniscus medialis, and the results were briefly described. Localization of the lesion demonstrated by CT was projected on the Schaltenbrand & Bailey's atlas in each of these patients and the deep brain structure involved was identified. The lesions were located mainly in the posterolateral thalamus including posteromedial part of the internal capsule (thalamic pain), however, they were located outside of the thalamus in some cases (suprathalamic pain). Two particular patients were described in detail because clinical courses, especially operative results were esteemed to be suggestive of an important role of lemniscal system in pain modulation. A 48-year-old man (Case 7) developed severe spontaneous burning pain on the right half of the body after extensive putaminal hemorrhage. Stimulation of the posterior limb of the internal capsule or of the thalamic sensory relay nuclei elicited no pain relief. Consequently a lesion was stereotaxically made in the most medial portion of the lemniscus medialis of the rostral mesencephalon. This operative procedure provoked previously unrecognized significant dysesthesia and hyperpathia predominantly of the extremities as well as aggravation of hypesthesia and hypalgesia. The second patient (Case 8) was a 44-year-old man who developed dysesthesia, hyperpathia and spontaneous pain of the left hand and face after hemorrhage in the right sensory cortex. Stimulation of the mesencephalic lemniscus medialis of the right side elicited comfortable warm sensation in contralateral upper half of the body including hand, fingers and face with simultaneous diminution of pain. These two cases were suggestive of the role of lemniscus medialis in pain modulation. Blockade of the lemniscus medialis elicited, and its facilitation inhibited the pain. Lemniscal and extralemniscal (spinothalamic) system have been proven to be intermingled in the thalamic and suprathalamic levels. Though both of the systems might be involved in the manifestation of central pain including our present ten cases, it was discussed and postulated that the facilitation of the lemniscal system might inhibit the activity of spinothalamic system, thus resulting in pain relief.