Papers of the Week

During the past few years, the research of chronic neuropathic pain has focused on neuroinflammation within the central nervous system and its impact on pain chronicity. As part of the ERA-Net NEURON consortium we aimed to identify immune cell patterns in cerebrospinal fluid (CSF) of patients with herpes zoster neuralgia (HZ) and polyneuropathy (PNP), which may contribute to pain chronicity in these neuropathic pain conditions.CSF of 41 patients (10 HZ, 31 PNP) was analyzed by flow cytometry identifying lymphocyte subsets: CD4+- (T-helper-cells), CD8+- (cytotoxic T-cells), CD19+- (B-cells), and CD56+- (natural killer; NK) cells. At baseline and at follow-up, the somatosensory phenotype was assessed with QST. Additionally, the patients answered epidemiological questionnaires and the PainDETECT. Immune cell profiles and somatosensory profiles, as well as PDQ-scores were analyzed and correlated in order to determine specific immune cell patterns, which contribute to chronic pain.We found a negative correlation (p= 0.004, r=-0.596) between the frequency of natural killer cells and mechanical pain sensitivity (MPS), one of the most relevant QST markers for central sensitization; a high frequency of NK-cells correlated with low MPS. The analysis of the individual follow-up showed a worsening of the pain condition if NK-cell frequency was low.Low NK-cell frequency is associated with signs of central sensitization (MPS), whereas high NK-cell frequency might prevent central sensitization. Therefore, NK-cells seem to play a protective role within the neuroinflammatory cascade and may be used as marker for pain chronicity.