Mirror-like spread of chronic pain linked to CNS changes

Evidence of altered interhemispheric conduction in a patient with mirror-like spread of chronic pain supports the theory that the spread of symptoms reflects a neurologic disease progression. The authors of the case report describe the controversy over the mechanisms of chronic pain spread. They say, "It is still debated whether the spread of symptoms reflects real progression of the disease rather than a somatoform sign associated with the psychological burden of chronic pain." Their neurophysiologic findings in a patient with complex regional pain syndrome (CRPS) that spread from one upper limb to another in a mirror-like fashion suggest that the spread of chronic pain is due to neurologic changes in the CNS. Magnetoencephalographic recordings showed that unilateral tactile stimuli elicited bilateral responses in the primary somatosensory cornices at the same time as the disease progressed to bilateral symptoms. The authors observe, "Such bilateral activation after unilateral stimuli is in striking contrast to the purely contralateral [primary somatosensory] activation observed in healthy subjects and suggests that the progression of CRPS symptoms was associated with pathologic interhemispheric spread of cortical activation."The CRPS occurred as a result of an electric shock from a meat cutter to the patient's right hand. The patient developed persistent pain, hyperalgesia, and autonomic symptoms within weeks of the accident, and, after seven years, similar symptoms appeared in the left upper limb. However, the symptoms developed abruptly in the left upper limb, in contrast to the gradual development of symptoms in the injured upper limb.Magnetoencephalographic recordings before the pain spread showed stimulation of the right index finger elicited a response in the contralateral parietal cortex, whereas recordings after the pain spread showed that stimulation of the right index finger elicited a bilateral response.The authors point out that the latency difference between the contra- and ipsilateral somatosensory responses (20 ms) agrees with the estimated conduction velocity of small callosal fibers connecting the distal parts of the hands. They consider that the mirror-like spread is possibly associated with increased commissural conductance, although the exact sites of this conduction cannot be confirmed from their data. Reference...