Biomarkers are tricky - the only thing I can think of is the role of the amygdala. Various studies have shown increased activity in pain states, and this makes sense in context of the amygdala being involved in generating fear and anxiety.

There are currently no robust biomarkers for either pain or anxiety, and I'm not sure how universal such a thing could be, as Jan mentioned, both conditions are very much dependent on previous experience, personality, and a range of other factors that are not easy to account for.

http://www.jmolecularpsychiatry.com/content/1/1/9

Thank both of you for reply.

according to rosie said, something happend in amygdala related to anxiety, yes i know. amygdala role also in descending pathway of neuropathic pain. so neuropathic pain alters the amygadala role. what type of molecular changes occured in amygadala. please let me know the molecular level of amygadala related to neuropathic pain induced anxiety. please tell me how to find out that level of study.

I am currently looking at cFos activation in the amygdala - it has already been shown in the spinal cord in neuropathic pain:

http://europepmc.org/abstract/MED/11293499/reload=0;jsessionid=xv40GljqeneApsJNvGj5.24

To be certain the activation in the amygdala is linked to pain, the activated neurons would require identification e.g. confirmation of excitatory or inhibitory, and identification of input/output regions.... and that these are differently activated in naive, sham, and neuropathic subjects ;)

Neuropathic pain is correlated with higher rates of depression and anxiety [Article Psychiatric co-morbidities in patients with chronic peripher...

Studies have also revealed a connection between anxiety and pain intensity in patients with pain disorders [Article Neuroinflammation and Comorbidity of Pain and Depression

Peripheral inflammation can trigger “sickness behavior” that includes symptoms such as pain, fatigue, affective disturbances, and sleep dysfunction. Increased levels of the proinflammatory molecules tumor necrosis factor (TNF) and interleukin-6 (IL-6) have been observed in patients with major depressive disorder, and higher levels of TNF were found in patients with comorbid neuropathic pain, compared with patients with pain without depression. [https://bit.ly/2AYSz5m]

Nicholson, B., & Verma, S. (2004). Comorbidities in chronic neuropathic pain. Pain medicine, 5(suppl_1), S9-S27.