Thalamic Imbalances Surprising

This article is hard to understand, given existing theory on the thalamus. Wallenberg sydrome is pain and other symptoms due to a stroke in the medulla.


Garcia Larrea et al from the Hospital Neurologique in Lyon France have reported what has to have every pain scientist scratching their heads.

They reported PET scan results in a patient with central pain as part of Wallenberg syndrome. The patient had a stroke on the left side. Over the short term, loss of sensation was noted on the right and also on the left, including the face. Loss on the right face went only as high as the third division of the trigeminal nerve, which would mean about to the upper lip or a little higher. Over time, the patient developed neuropathic pain on the left face, but retained loss of sensation on the right side. This appears, at first, to violate Boivie’s rule, which is that “one must lose some sensation to become a candidate for severe central pain”, except that there was LIGHT sensory loss on the left as well, so Boivie’s rule is not touched, we just are reminded that light touch loss is more likely to be associated with neuropathic pain than profound diminution in the sense of touch. The sensory loss was dissociated side to side from the neuropathic pain!

Obviously everyone would wonder what is going on in this patient’s thalamus. The results were not only surprising, they were staggering. There was decreased blood flow to the RIGHT thalamus, OPPOSITE to the painful left side. Three months of motor cortex stimulation was given and the patient reported sixty percent reduction in the left facial pain (we don’t like the number sixty, a patient can be torqued to say this much). At the time of the sixty percent improvement the thalamic asymmetry in blood flow had been eliminated. It may be coincidence, or it may be the first real proof we have that central pain probably stems from abnormal signals in the thalamus, imbalance being one of the possible ones. The authors concluded that PET hypoactivity in the thalamus contralateral (opposite side) to the pain reflects not only loss of sensation but provides clues as the pain pathophysiology. We certainly would like to see more studies such as this.

Rationally, it has come to the time when ALL patients with severe Central Pain should have serial functional MRI, but with managed care ripping and tearing through American Medicine toward the bottom line they can show to investment bankers, such patients will probably be lucky to see a doctor who believes them, let alone get functional MRI or PET scanning of the brain.