Decreased central mu-opioid receptor availability in fibromyalgia

Abstract

The underlying neurophysiology of acute pain is fairly well characterized, whereas the central mechanisms operative in chronic pain states are less well understood. Fibromyalgia (FM), a common chronic pain condition characterized by widespread pain, is thought to originate largely from altered central neurotransmission. We compare a sample of 17 FM patients and 17 age- and sex-matched healthy controls, using mu-opioid receptor (MOR) positron emission tomography. We demonstrate that FM patients display reduced MOR binding potential (BP) within several regions known to play a role in pain modulation, including the nucleus accumbens, the amygdala, and the dorsal cingulate. MOR BP in the accumbens of FM patients was negatively correlated with affective pain ratings. Moreover, MOR BP throughout the cingulate and the striatum was also negatively correlated with the relative amount of affective pain (McGill, affective score/sensory score) within these patients. These findings indicate altered endogenous opioid analgesic activity in FM and suggest a possible reason for why exogenous opiates appear to have reduced efficacy in this population.

Figure 1.

Reduced MOR BP in FM patients. A–C, Regions showing reduced MOR BP: left NAc (L Nac; A), left amygdala (L Amy; B), and right dACC (R dACC; C). Plots of individual MOR BP values extracted from PET images are depicted to the right of each corresponding region of interest. FM and healthy control (HC) participants are shown in black and white circles, respectively.

Figure 2.

MOR BP is negatively correlated with affective pain. The scatter plot of left accumbens (L Nac) MOR BP and clinical pain (SF MPQ, affective score) reveals a significant negative correlation (r = −0.53; p < 0.05).

Figure 3.

Relative magnitude of the affective pain dimension is associated with reduced MOR BP throughout the cingulate and striatum in FM. A–C, Regions showing significant correlations with SF MPQ affective/sensory (Aff/Sens) scores: left dACC and pCC (A), right aCC (B), and right putamen (Put; C). Scatter plots of individual MOR BP values extracted from PET images are plotted against affective/sensory scores below each image.