Fig. 2.

Graphical representation of the literature search results and potential key biological processes underpinning the interconnectivity among fatigue, cognitive impairment, depression, and pain. The potential links between the biological processes and symptoms are color-coded, e.g., a blue circle or line indicates a link with depression. References shown in the colored boxes support the relationships represented in the figure. The dashed gray lines and associated references represent the way in which each of the biological mechanisms may directly impact the others. HPA, hypothalamic-pituitary-adrenal