Part 1: Introduction
The chronic pain medical treatment guidelines apply when the patient has chronic pain as determined by following the clinical topics section of the Medical Treatment Utilization Schedule (MTUS). In following the clinical topics section, the physician begins with an assessment of the presenting complaint and a determination as to whether there is a “red flag for a potentially serious condition” which would trigger an immediate intervention. Upon ruling out a potentially serious condition, conservative management is provided and the patient is reassessed over the next 3-4 weeks. If the complaint persists during this interval, the physician needs to reconsider the diagnosis and decide whether a specialist evaluation is necessary. The chronic pain medical treatment guidelines apply to patients who fail to recover and continue to have persistent complaints without definitive treatment, such as surgical options. This provides a framework to manage all chronic pain conditions, even when the injury is not addressed in the clinical topics section of the MTUS.
The chronic pain medical treatment guidelines consist of two parts. Part 1 is the introduction. Part 2 consists of pain interventions and treatments. With a few exceptions, Parts 2 is primarily an adaptation of evidence-based treatment guidelines, from the Work Loss Data Institute’s Official Disability Guidelines (ODG) Treatment in Workers’ Comp – Chapter on Pain (Chronic). The version adapted is dated October 31, 2007, and it is being adapted with permission from the ODG publisher. Any section not adapted directly from ODG is labeled “[DWC]”.
Chronic Pain: Chronic pain is defined as “any pain that persists beyond the anticipated time of tissue healing.”
Types of Pain: Pain mechanisms can be broadly categorized as nociceptive or neuropathic.
Nociceptive pain: Nociceptive pain is the pain caused by activation of nociceptors, which are sensory neurons found throughout the body. A nociceptor is “a receptor preferentially sensitive to a noxious stimulus or to a stimulus which would become noxious if prolonged.”
Neuropathic Pain: Neuropathic pain is “pain initiated or caused by a primary lesion or dysfunction of the nervous system.” Normal nociception would not be considered dysfunction of the nervous system.
Chronic pain has a huge impact on the individual and society as a whole. It is the primary reason for delayed recovery and costs in the workers’ compensation system. Most chronic pain problems start with an acute nociceptive pain episode. Therefore, effective early care is paramount in preventing chronic pain. Given the importance of pain in healthcare, it is presently the subject of intensive scientific research which in turn has generated a growing evidence base regarding the diagnosis, treatment and management of painful conditions.
The International Association for the Study of Pain (IASP) states that pain is “an unpleasant sensory or emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” (Merskey and Bugduk 1994) This describes pain as a subjective experience; therefore, unlike hypertension or diabetes, there is no objective measurement for pain intensity. Analysis of the objective data (psychosocial assessment, physical exam findings, imaging results, lab tests) is needed to evaluate the patient’s subjective report of pain.
The experience of pain is a complex phenomenon. Multiple models have evolved over time to explain it. Traditionally, the biomedical model explains pain through etiologic factors (e.g. injury) or disease whose pathophysiology results in pain. It is now understood that this classic biomedical approach to understanding and treating pain is incomplete. Its exclusive application can result in unrealistic expectations on the part of the physician and patient, inadequate pain relief, and excessive disability in those with pain that persists well after the original injury has healed.
The biopsychosocial model of pain instead recognizes that pain is ultimately the result of the pathophysiology plus the psychological state, cultural background/belief system, and relationship/interactions with the environment (workplace, home, disability system, and health care providers). Current research is investigating the neurobiological causes for persistent pain and how structural and functional changes in the central nervous system may serve to amplify and maintain the experience and disability of certain pain condition. (Siddall and Cousins 2007) This is an area of intensive research which will contribute to the scientific evidence base in years to come.
Within the biomedical model, pain mechanisms are broadly categorized as nociceptive or neuropathic. Inflammatory mechanisms may also play a role. While there are similarities, each mechanism has unique features and characteristics. This mechanistic approach may provide greater insight into appropriate therapeutic strategies.
Several reviews have detailed the mechanisms and mediators of pain and the components of the ascending and descending pain pathways. In nociceptive pain, signal transduction in nociceptor somatosensory afferent terminals converts mechanical, electrical, thermal, or chemical energy into an action potential which is transmitted to the dorsal horn of the spinal cord by specialized nerve fibers. The signal is then transmitted through ascending cortical pathways to the brain. Nociceptive signals within the brain are sent to two major areas: the somatosensory cortex, where the sensory component of pain is represented in the brain, and the limbic forebrain system, which is the neural substrate for the emotional component of pain experience responsible for feelings of suffering.
Since these areas of the brain interact with other areas of the brain, past memories, external environmental factors, and internal cognitive factors (i.e. psychosocial factors) influence or modulate the pain experience. How the brain integrates all the input is, in part, the basis for the biopsychosocial approach to the management of pain.
Neuropathic pain is “pain initiated or caused by a primary lesion or dysfunction of the nervous system.” (Turk and Okifuji 2001) The altered modulation of the pain response in patients with neuropathic pain causes a state of hyperexcitability and continuous pain signal output in the absence of peripheral tissue damage. “‘Neuropathic pain can result from injury or trauma (e.g. surgery), infection (e.g. post herpetic neuralgia), endocrine (e.g. diabetes, hypothyroidism), demyelination (e.g. multiple sclerosis), errors in metabolism, neurodegenerative disorders (e.g. Parkinson’s disease), or damage directly to the spinal cord or brain (e.g. thalamic stroke).’ (Backonja in Loeser, 2001)” (Mackey and Maeda 2004)