Functional Dyspepsia (FD) is a prevalent “functional somatic syndrome” (FSS) defined by chronic epigastric symptoms in the absence of organic abnormalities likely to explain them.
Co-morbidity with mood and anxiety disorders is high, as well as with other FSS, DSM-IV “somatoform disorders” and, potentially, DSM-V “somatic symptom disorders” (SSD). FD is
characterized by abnormal regional cerebral activity in cognitive/affective pain modulatory circuits, but it is unknown which neurotransmitter systems are involved. We aimed to assess and compare in vivo cerebral cannabinoid-1 (CB1) receptor availability between FD patients
and age-, gender- and BMI-matched healthy controls.
Twelve FD patients and 12 matched healthy controls were investigated using positron emission tomography (PET) with the CB1 receptor radioligand [18F]MK-9470. Nine of the
patients received a second PET scan after a naturalistic follow-up period of 36±9.6 months (range: 25.2 – 50.4 months).
FD patients had significantly higher CB1 receptor availability in cerebral regions involved in
(visceral) nociception (brainstem, insula, anterior cingulate cortex) as well as in homeostatic
and hedonic regulation of food intake [hypothalamus, (ventral) striatum] (p<0.05 corrected for multiple testing, region of interest analysis), which persisted after a follow-up period of 36±9.6 months.
These findings suggest that the abnormal brain activity in several of these regions, previously demonstrated in FD, may be due to sustained endocannabinoid system dysfunction, identifying it as a potential novel target for treatment and warranting further studies to elucidate whether it is also a feature of other FSS or, more generally, SSD.