Pain in the absence of any pathophysiologic cause or injury
The clinician’s search for a pain diagnosis is typically predicated on the notion that there must be an underlying tissue injury of severity equal to the severity of the patient’s pain complaints. This approach to a pain evaluation rests on 2 assumptions that are not true for all patients:
- Pain is simply a sensory experience that is always caused by tissue damage of some type.
- The severity of the pain experienced by a patient should be tightly bound to the severity of the pain stimulus (ie, tissue damage).
These assumptions are true of acute nociceptive pain, they may or may not be true for NPP, but they do not apply to the third type of pain—pain for psychological reasons. While tissue pathology in humans and animals with nociceptive pain is usually visible, measurable, and correlates with observed pain behaviors, the damage to nerve tissue and the ensuing changes in nervous system function with NPP are not always visible or able to be imaged. These changes produce pain that can appear more severe than expected based on a brief exam. Some of the time, however, characteristic symptoms and physical signs of NPP will be present, and perhaps electrodiagnostic or other tests will be abnormal, thus providing some objective sense of changes in nervous system function.
In contrast, pain behavior due to the third type of pain usually appears very much out of proportion, and unbound to, tissue pathology. Furthermore, the patient’s pain behaviors often reflect heightened emotional pain processing (TABLE 29). The resulting emotionally charged presentation can be alarming and suggestive of extreme tissue injury, but there may be absolutely no evidence of tissue injury or pathology.
Functional change in the CNS
There is evidence from experimental studies that psychologic factors change nervous system function. In one review, the authors concluded, “Pain…can vary widely between people and even within an individual depending on…the psychological state of the person.”10 In a second review, the authors concluded that our emotional state has an enormous influence on pain; a negative emotional state increases pain, whereas a positive state lowers pain.11
But can psychological factors induce long-term changes in nervous system function analogous to the systems neuroplasticity responsible for irreversible changes in NPP? And can psychologically induced changes in nervous system sensory processing lead to pain without any tissue or nerve damage?
We theorize that a functional change in the CNS can occur in response to certain emotional states or traumatic experiences (eg, child abuse, assault, accidents). (More on this in a bit.) When such changes occur, mildly painful stimuli are amplified and processed through overly sensitized, dysregulated, ramped-up emotional and somatosensory pain circuits in the brain. This is analogous to the functional changes in the nervous system that occur with NPP; however, when the nervous system changes are due to psychological factors, there may be no tissue or nerve injury.