Breakthrough pain is usually classified according to its relationship to specific events [1]:

• Spontaneous pain (also known as “idiopathic pain”) – this type of pain occurs unexpectedly.
• Incident pain (also known as “precipitated pain” or, when appropriate, “movement-related pain”) – this type of pain is related to specific events, and can be sub-classified into three categories:

1. Volitional incident pain - is precipitated by a voluntary act (e.g. walking).
2. Non-volitional incident pain - is precipitated by an involuntary act (e.g. coughing).
3. Procedural pain - is related to a therapeutic intervention (e.g. wound dressing).

In the past “end-of dose failure” was often considered to be a subtype of breakthrough pain. End-of-dose failure describes an exacerbation of pain that occurs prior to the next dose of the background analgesic, and reflects declining levels of the background analgesic. However, now many experts believe that end-of-dose failure is not a subtype of breakthrough pain, since they perceive that end-of-dose failure represents inadequately controlled background pain (see Definition section) [2].

References

[1]. Davies A. Introduction. In: Davies A, editor. Cancer-related breakthrough pain. Oxford: Oxford University Press; 2006. p. 1-11.

[2]. Davies AN, Dickman A, Reid C, Stevens AM, Zeppetella G. The management of cancer-related breakthrough pain: recommendations of a task group of the Science Committee of the Association for Palliative Medicine of Great Britain and Ireland. European Journal of Pain 2009; 13(4): 331-8.