Relevance of spinal neuroinflammation to neuropathic pain: an exploratory clinical study evaluated by ¹¹C-DPA-713 PET and TSPO-related biomarkers.

Objectives: Some preclinical studies revealed that the translocator protein (TSPO) was upregulated in astrocytes and microglia of the spine in a model of neuropathic pain. In the present study, we evaluated TSPO-PET in the patients with pure neuropathic pain to validate the relevance of spinal neuroinflammation. Methods: Five healthy controls (HC) and five patients with pure neuropathic pain (NP) diagnosed by the IASP guideline were enrolled in the present study. After measuring TSPO-related biomarkers (plasma 24-OHC and BDNF), spinal ¹¹C-DPA-713 PET were conducted in all subjects. Patients with neuropathic pain completed the questionnaires for pain symptom before and after PET examination, assessing BPI, HADS, Pain DETECT, Pain drawing, and NRS.

Results: In NP group, averaged Pain DETECT score was 19.2 before PET examination. Both of averaged SUV_max and SUV_mean of ¹¹C-DPA-713 uptake did not show significant differences between HC (1.44 ± 0.14 and 1.06 ± 0.08) and NP group (1.35 ± 0.30 and 1.05 ± 0.25). Plasma 24-OHC and BDNF did not show significant differences between HC and NP group without significant correlations with ¹¹C-DPA-713 uptakes.

Conclusions: The present exploratory study revealed that no definite evidence of spinal neuroinflammation was observed in the pure neuropathic pain. Therapeutic intervention for inhibition of spinal microglia and astrocyte activation would not be effective to relieve the symptom from neuropathic pain.

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