Stimulus-Dependent and Spontaneous Pain

I think that one of the key things we should look for in the patient assessment is the behaviour of pain. Is the pain Stimulus-dependent and/or Spontaneous pain.

The “evoking” of pain can be an important aspect to ascertain in the subjective and objective examination. The diagrams at the end of this post (from Costigan et al, 2009) summarise the different pain states in regards to this.

As can be seen, Nociceptive pain is reported to only occur in response to a painful/noxious stimulus. In a purely Nociceptive pain state there should be no evidence of spontaneous pain or pain arising from a non-painful stimulus (e.g. Allodynia). That is, it is purely Stimulus-Dependent. I would also describe Nociceptive pain as Mechanical pain. e.g. If I move my sore shoulder in the painful direction it hurts. If I don’t move it in that direction I doesn’t hurt.

In comparison, Inflammatory, Neuropathic and Dysfunctional/Functional pain can demonstrate spontaneous pain, pain arising from a non-painful stimulus (Allodynia) and pain hypersensitivity (Hyperalgesia). They can also show Stimulus-dependent pain. Whilst constancy of pain is not referred to in any of the references I have read, I would assume that these three pain states/types can also demonstrate constant pain given that they can demonstrate spontaneous pain.

Certainly a mix of pain types can occur, and just because someone has constant pain does not mean they do not have a significant mechanical/nociceptive component.

I have referred to “Mechanical” pain above as Nociceptive pain. I think we can also use the term “Non-mechanical” pain. This would relate to symptoms that are constant in nature and/or occur without a stimulus. Based on this post we could place Inflammatory, Neuropathic and Dysfunctional/Functional pain.

How I feel we can identify pain types will be covered in the next post in regard to my subjective framework for identifying pain type(s). The key message that I take from the above is that if a patient is reporting spontaneous and/or constant pain that they must have an Inflammatory, Neuropathic or Dysfunctional/Functional pain component to their presentation. Alternatively they may have elements of peripheral or central sensitisation, but as discussed previously, these pain mechanisms are more likely to occur in Inflammatory, Neuropathic or Dysfunctional/Functional pain states.

Any thoughts?

These are the diagrams from Costigan et al (2009):

References:

• Costigan M, Scholz J, Woolf CJ (2009). Neuropathic pain: a maladaptive response of the nervous system to damage. Annu. Rev. Neurosci. 32 (1-32).