IL-6 and hsCRP in Somatic Symptom Disorders and related disorders

Interleukin 6 (IL-6) and high-sensitivity C-reactive protein (hsCRP) are biomarkers of systemic low-grade inflammation (SLI) in depression and anxiety. The question if SLI in those conditions is related to comorbid chronic medical conditions has not been resolved. DSM-5 Somatic symptom disorders and related disorders (SSRD) are conditions with serious distress related to physical symptoms as main criterion. They can occur in patients with medically unexplained symptoms (MUS) and in patients with known comorbid chronic medical conditions. Often, comorbid depression and anxiety are present. SSRDs offer the opportunity to explore the role of SLI in relation to mental distress, including trauma, MUS, chronic medical conditions and comorbid mental disorder.

We hypothesized that increased IL-6 and hsCRP may be directly linked to SLI in SSRD, and that comorbid chronic medical conditions, childhood trauma, current stress and comorbid depression and anxiety may be risk factors that account for some of the variance of SLI in SSRD.

We explored these relationships in a large sample of 241 consecutive outpatients with SSRD.

Mean hsCRP level was 3.66 ​mg/l, and mean IL-6 level was 3.58 ​pg/ml. IL-6 and hsCRP levels were associated with each other: τ ​= ​0.249, p ​< ​.001; a medium size correlation. Comorbid chronic medical conditions, adverse childhood events other than sexual trauma, and current stress levels were not associated with IL-6 or hsCRP levels.

IL-6 and hsCRP are elevated in SSRD, indicating SLI in SSRD independently of comorbid chronic medical conditions. In clinical research, elevated IL-6 and hsCRP can be used as biomarkers of SLI and can indicate risk for childhood sexual abuse in SSRD. Elevated hsCRP may be a biomarker indicating risk for comorbid depression or high pain levels in SSRD as well.