Postherpetic neuralgia (PHN) is a debilitating
chronic pain condition, yet there is a lack of knowledge regarding underlying brain activity. Here we identify brain regions involved in spontaneous
pain of PHN (n=11) and determine its modulation with
Lidoderm therapy (patches of 5%
lidocaine applied to the PHN affected body part). Continuous ratings of fluctuations of spontaneous
pain during fMRI were contrasted to ratings of fluctuations of a bar observed during scanning, at three sessions: (1) pre-treatment baseline, (2) after 6h of
Lidoderm treatment, and (3) after 2 weeks of
Lidoderm use. Overall brain activity for spontaneous
pain of PHN involved affective and sensory-discriminative areas: thalamus, primary and secondary somatosensory, insula and anterior cingulate cortices, as well as areas involved in emotion, hedonics, reward, and punishment: ventral striatum, amygdala, orbital frontal cortex, and ventral tegmental area. Generally, these activations decreased at sessions 2 and 3, except right anterior insular activity which increased with treatment. The sensory and affective activations only responded to the short-term treatment (6h of
Lidoderm); while the ventral striatum and amygdala (reward-related regions) decreased mainly with longer-term treatment (2 weeks of
Lidoderm).
Pain properties: average magnitude of spontaneous
pain, and responses on
Neuropathic Pain Scale (NPS), decreased with treatment. The ventral striatal and amygdala activity best reflected changes in NPS, which was modulated only with longer-term treatment. The results show a specific brain activity pattern for PHN spontaneous
pain, and implicate areas involved in emotions and reward as best reflecting changes in
pain with treatment.