Copyright © 2013 by Saunders, an imprint of Elsevier Inc. Chapter 8: Neuropathic Pain, Pain Matrix Dysfunction, and Pain Syndromes Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Chronic Pain as a Disease Pain involves inhibitory and excitatory circuits in the CNS that either diminish or amplify pain messages. Neural mechanisms for regulating pain amplify signals, creating pain in the absence of noxious stimuli in neuropathic pain, pain matrix dysfunction, and pain syndromes. Pathologic pain has no beneficial biological function. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Four types of Chronic Pain Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Copyright © 2013 by Saunders, an imprint of Elsevier Inc. Neuropathic Pain International Association for the Study of Pain defines neuropathic pain as “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system.” Individuals with genetic codes that produce less of the enzyme that regulates the levels of catecholamine and encephalin are twice as likely to develop neuropathic pain as those who produce more of the enzyme. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Symptoms of Neuropathic Pain Paresthesia: painless abnormal sensation in the absence of nociceptor stimulation Dysesthesia: unpleasant abnormal sensation, either evoked or spontaneous Allodynia: pain evoked by a stimulus that normally would not cause pain Secondary hyperalgesia: excessive sensitivity to stimuli that are normally mildly painful in uninjured tissue Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Five Mechanisms Produce Neuropathic Pain Ectopic foci Ephaptic transmission Central sensitization Structural reorganization Altered top-down modulation Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Mechanisms of Neuropathic Pain Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Copyright © 2013 by Saunders, an imprint of Elsevier Inc. Ectopic Foci When myelin is damaged, signals from the exposed axon stimulate excessive production of mechanosensitive and chemosensitive ion channels. Channels are inserted into the demyelinated membrane, producing abnormal sensitivity to mechanical and chemical stimuli. Demyelinated regions take on the new, pathologic role of generating action potentials in addition to the normal role of conducting action potentials. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Ephaptic Transmission Cross-talk between axons in regions of demyelination Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Central Sensitization Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Structural Reorganization Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Sites that Generate Neuropathic Pain Neuropathic pain can arise from abnormal neural activity in the following: Periphery (e.g., nerve compression in carpal tunnel syndrome) CNS in response to deafferentation Dorsal horn Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Peripheral Generation of Neuropathic Pain Injury or disease of the peripheral nerves often results in sensory abnormalities. Complete nerve resection results in a lack of sensation from that nerve’s receptive field. Partial damage can result in allodynia and sensations similar to an electric shock. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Peripheral Generation of Neuropathic Pain Peripheral abnormalities causing neuropathic pain include the following: Development of ephaptic transmission that occurs in demyelinated regions Ectopic foci in an injured nerve that occurs at the nerve stump, in areas of myelin damage, or in dorsal root ganglion somas Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Central Response to Deafferentation Deafferentation can be complete or partial. Neurons in the CNS may become abnormally active when peripheral sensory information is completely absent. Avulsion of dorsal roots from the spinal cord produces deafferentation and causes an individual to feel burning pain in the area of sensory loss. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Central Response to Deafferentation Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Copyright © 2013 by Saunders, an imprint of Elsevier Inc. Phantom Pain Phantom limb sensation refers to individuals who have had a limb amputated but experience sensations that seem to originate from the missing limb. Phantom sensation that is painful is called phantom pain; reports of this are more rare. Phantom pain must be differentiated from residual limb pain; treatment for residual limb pain is different than for phantom limb pain Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Copyright © 2013 by Saunders, an imprint of Elsevier Inc. Central Pain Central pain is caused by a lesion of the CNS and is usually localized to the area of the body deafferented by the lesion. Neuropathic central pain refers to burning, shooting, aching, freezing, or tingling pain. SCI central pain: the thalamus may be the site of pain generation because after a SCI, the neurons in the VPL thalamic nucleus are spontaneously active without input from the spinal cord. MS central pain depends on the location of the lesion. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Pain Matrix Dysfunction Top-down regulation of pain is disturbed when the pain matrix malfunctions. Antinociception is reduced and/or pronociception is intensified; the result is increased pain. Fibromyalgia, episodic tension-type headache, migraine, and chronic whiplash-associated disorder involve disturbance of top-down regulation of pain. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Copyright © 2013 by Saunders, an imprint of Elsevier Inc. Fibromyalgia Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Episodic Tension-Type Headache Criteria for ETTH: Mild-to-moderate pain, usually bilateral Lasting 30 minutes to 7 days Not aggravated by physical activity Not associated with nausea or vomiting Photophobia or phonophobia, but not both, may accompany the headache. Mechanism appears to be supersensitivity to nitric oxide. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Copyright © 2013 by Saunders, an imprint of Elsevier Inc. Pain Syndromes Two syndromes involve other systems in addition to the pain system: Complex regional pain syndrome involves the somatosensory, autonomic, and motor systems. Chronic low back pain syndrome involves muscle guarding, disuse, and abnormal movements. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Complex Regional Pain Syndrome Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Complex Regional Pain Syndrome Former names Causalgia Shoulder-hand syndrome Sympathetically maintained pain Reflex sympathetic dystrophy Sudeck’s atrophy Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Chronic Low Back Pain Syndrome Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Surgical Treatment of Chronic Pain In theory, dorsal rhizotomy should alleviate pain; however, it often fails in practice. Persistence of pain after spinothalamic tractotomy may be the result of CNS changes in response to the original maintained pain or to pain-mediating fibers traveling in the dorsal columns. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Pharmacological Treatment of Pain Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Psychologic Factors in Chronic Pain Expectations, cognition, and emotions affect the experience of pain. Anxiety, depression, and catastrophizing predict reactions to pain and the ability to cope with pain. Amount of pain an individual expects influences the processing in both the medial and lateral pain systems. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Psychologic Factors in Chronic Pain Therapists must address all three Ds of chronic pain: Distress Disuse Disability Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Psychologic Factors in Chronic Pain Psychologic interventions may decrease activation of the pain system and also improve coping skills. Relaxation (breathing, muscle relaxation) Biofeedback Imagery Cognitive behavioral therapy Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Psychologic Factors in Chronic Pain Placebo-associated improvement is defined as, “any genuine psychological or physiologic effect which is attributable to receiving a substance or undergoing a procedure, but is not due to the inherent powers of that substance or procedure”. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Psychologic Factors in Chronic Pain Approaches include: Providing positive (yet honest) communication about the therapy. Providing encouragement and education. Developing trust, compassion, and empathy. Understanding the person as an individual. Creating rituals that provide meaning and expectancy for the person. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Conflicts Between Patient and Provider Goals People with chronic pain often want health care providers to acknowledge them as individuals and to have their pain recognized as biologically based. Health care providers are frequently more concerned with the diagnosis and treatment than with providing biological explanations for chronic pain. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.

Conflicts Between Patient and Provider Goals Most important factor in achieving a positive patient–physical therapist interaction is the therapist’s ability to explain treatment recommendations in a way that is consistent with the patient’s existing beliefs about his or her chronic pain. Copyright © 2013 by Saunders, an imprint of Elsevier Inc.