Chasing map plasticity in neuropathic pain.

OBJECTIVE: Recently, somatosensory cortex stimulation has been proposed as a possible treatment for neuropathic deafferentation pain, based on a simple 4-step concept: (1) pain is associated with increased activity in the somatosensory cortex, (2) allodynia-evoked blood-oxygen-level dependence functional magnetic resonance imaging (fMRI) activation depicts the area involved in the pain, (3) if fMRI-guided, neuronavigation-based transcranial magnetic stimulation can transiently suppress the pain, then (4) an extradural electrode can be implanted targeting the same area. CASE DESCRIPTION: A patient who was successfully treated with this approach for over 6 years for trigeminal anesthesia dolorosa associated with a subjectively malpositioned eye after multiple recurrent facial skin tumor removals developed new pain after more extensive surgery. Reprogramming the implanted electrode was unsuccessful. The presence of the electrode yielded too many artifacts on a renewed fMRI, and therefore a positron emission tomography (PET) scan was performed under evoked allodynia. Fusing the previous fMRI with the new PET images depicted 2 novel targets for stimulation, 1 anterior and 1 posterior of the previous target and beyond the spatial configuration of the implant. After the addition of 2 new electrodes, the pain could again be controlled in a placebo-controlled way, but only when the 2 electrodes were activated.
CONCLUSIONS: Combining fMRI and PET scanning can potentially demonstrate continuing map plasticity under progressive somatosensory deafferentation. The functional imaging data can be used as target for pathophysiology-based somatosensory cortex stimulation.