Analysis of the perception of and reactivity to pain and heat in patients with Wallenberg syndrome and severe spinothalamic tract dysfunction

Background-The aim of the study was to assess the consequences of severe sp inothalamic tract lesions resulting from lateral medullary infarct and to s how that a specific pain perception can be elicited by strong thermal stimu lation. Case Descriptions-Both patients examined presented with severe thermoalgic dissociation of the limbs contralateral to the lesion, with normal discrimi native somatosensory perception and motor strength. They reported pain perc eption when touching very warm (>50 degrees C to 60 degrees C) objects and a brisk, occasionally uncontrolled withdrawal reaction of the arm and hand under the same conditions, without any perception of the heat nature of the stimulus. Warm stimulation, <45 degrees C, elicited no thermal perception or discrimination. Pain perception could be elicited in both patients by in creasing the temperature, with a reproducible threshold of 47 degrees C to 49 degrees C. Pain always occurred after a prolonged delay of 8 to 10 secon ds in response to threshold heat, and was described as deep and osseous, an d clearly different from that perceived on the nonaffected side. The delay was much shorter when the temperature was increased by 4 degrees C to 5 deg rees C. Cold stimulation elicited similar pain perception in one patient. A nalysis of subjective perception of laser stimulation showed a much higher pain threshold on the affected hand. There were no laser-evoked potentials on this side, which suggested major spinothalamic injury. Assessment of the RIII noxious reflex revealed persistent response withdrawal reactions, wit h an increased threshold on the affected side, and partial consciousness of the noxious nature of the stimulus. Conclusions-To our knowledge, this is the first description of the appearan ce of pain perception of high temperatures in patients with severe spinotha lamic injury who are suffering from a complete loss of temperature percepti on. This implies that noxious thermal stimulation can still be perceived vi a extra spinothalamic pathways (which are slow and multisynaptic), such as the spinoreticulothalamic tract. Patients with Wallenberg syndrome should b e informed and made aware of their residual perception of and reactions to noxious stimulation.