Nondermatomal somatosensory deficits in patients with chronic pain disorder: Clinical findings and hypometabolic pattern in FDG-PET

Patients with chronic pain disorders often show somatosensory disturbances that are considered to be functional. This paper aims at a more precise clinical description and at a documentation of functional neuroimaging correlates of this phenomenon. We examined 30 consecutive patients with unilaterally accentuated chronic pain not explained by persistent peripheral tissue damage and ipsilateral somatosensory disturbances including upper and lower extremities and trunk. The patients were assessed clinically and with conventional brain CT or MRI scan. In the last 11 patients functional neuroimaging was carried out (18-fluordeoxyglucose positron emission tomography = FDG-PET). Depressive symptoms were assessed with the Hamilton depression scale (HAMD-17) and pain intensity was rated with a visual analogue scale for pain (VAS). All patients suffered from mild to moderate depressive symptoms. All patients had experienced a prolonged antecedent phase of severe emotional distress; most of them remembered a “trigger episode of somatic pain” on the affected side. Somatosensory deficits were a replicable hyposensitivity to touch and heat perception of nondermatomal distribution. Conventional imaging procedures (brain CT or MRI scans) showed no structural changes. However, in 11 patients functional imaging with FDG-PET showed a significant hypometabolic pattern of changes in cortical and subcortical areas, mainly in the post-central gyrus, posterior insula, putamen, and anterior cingulate cortex. In summary, pain-related nondermatomal somatosensory deficits (NDSDs) are a phenomenon involving biological as well as psychosocial factors with replicable neuroperceptive clinical findings and a complex neurodysfunctional pattern in the FDG-PET. Abbreviations: ACC: anterior cingulate cortex; CRPS: complex regional pain syndrome; DLPFC: dorsolateral prefrontal cortex; DSM-IV: diagnostic and statistical manual of mental disorders, fourth revision; FDG-PET: 18-fluordeoxyglucose positron emission tomography; fMRI: Functional magnetic resonance imaging; HAMD: Hamilton depression scale; ICD-10: International classification of diseases, version 10; NDSD: nondermatomal somatosensory deficits; PFC: prefrontal cortex; PTSD: posttraumatic stress disorder; SPECT: single photon emission computerized tomography; SPM: Statistical parametric mapping; VAS: visual pain analogue scale.