I have been asked the above question hundreds of times, in one form or another, by patients, attorneys, or insurers.
The reality is that pain symptoms are by definition subjective. They are after all symptoms, akin to the symptoms that one might experience after having a stroke. To document objective evidence of pain requires expensive testing of the central nervous system, which is not the standard of care, and in a non research setting would be considered medically unnecessary. However, the research has already been done and is readily available.
Chronic back pain is one of the most frequent reasons for permanent impairment in people under age 65, and yet is considered a subjective symptom and often denigrated as unprovable by third party insurers, who seek “objective” evidence of disability. The reality is that chronic pain is associated with reduced brain gray matter and impaired cognitive ability, which is reversible with appropriate and adequate treatment.
Evidence suggests that the mechanisms of chronification of pain are related to cortical reorganization, an objective functional neuroplasticity change.
Brain neuro-imaging with structural MRI in patient’s experiencing chronic low back pain documents a significant decrease of gray matter in the brainstem and the somatosensory cortex which correlates with increasing intensity of pain. Interestingly an increase in gray matter bilaterally in the basal ganglia and the left thalamus, the pain transmission centers, also correlates with increasing intensity of pain. These data support the hypothesis that ongoing nociception is associated with cortical and subcortical reorganization on a structural level, which may play an important role in the process of the chronification of pain, and that the thalamic pain processing center increases in size and functionality.
Appropriate and adequate treatment of chronic pain reverses many of these functional and structural brain abnormalities, and restores gray matter in the brainstem and the somatosensory cortex.
Affective components and intensity of pain correlate with structural differences in gray matter in chronic back pain patients, T. Schmidt-Wilcke, et al. May; PAIN Volume 125, Issue 1 , Pages 89-97, November 2006
Effective Treatment of Chronic Low Back Pain in Humans Reverses Abnormal Brain Anatomy and Function
David A. Seminowicz, et al. The Journal of Neuroscience, 18 May 2011, 31(20): 7540-7550; doi: 10.1523/JNEUROSCI.5280-10.2011