Table 1 Explanation of aspects of CS

Dorsal horn of the spinal cord: in case of CS, sensory signals from the body can be increased in the dorsal horn, due to structural and functional changes, as an increase of receptors and neurotransmitters [8].

Ascending and descending pathways: sensory signals from the body go through afferent nerves to the dorsal horn of the spinal cord and further through ascending pathways to the brain. These signals are processed in the brain and are sent back to the body through the descendent pathways. The brain can increase the signals in case of danger, and inhibit them in case of no alarm. In case of CS there is reduced inhibition.

Hyperalgesia: increased sensitivity to painful stimuli

Allodynia: painful perception of non-painful stimuli

Temporal summation (TS): TS refers to the phenomenon of increased pain perception in response to repetitive noxious stimuli over time. In case of CS the amplification of stimuli in the ascending neuronal pathways leads to an increase of TS [9,10,11,12].

Conditioned pain modulation (CPM): CPM refers to the phenomenon that ‘pain inhibits pain’, the reduction in experienced pain for a tested stimulus due to the interference of a second stimulus (conditioning stimulus) applied at the same time but to a remote body location. In case of CS CPM will show a smaller reduction in pain sensitivity due to hyperexcitability of the central nervous system and reduction of descending inhibition [13,14,15].