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Neuroanatomic
Acupuncture for Pain Objectives
Key Points
Overview What Is Neuropathic Pain? Neuropathic pain arises from neuropathic nerves-that is, nerves which have suffered damage or injury. Neuropathy can arise from damage to the nerve secondary to neoplasia, toxins, inflammation, degeneration, trauma, vascular compromise, infections, and metabolic derangements. While the central nervous system (CNS) resides within the protective (though sometimes restrictive) bony casement of the cranium and vertebrae, the delicate tissues comprising the peripheral nervous system lay vulnerable to trauma by compression, irritation, stretching, angulation, and friction. One of the most vulnerable and commonly impacted elements of the peripheral nervous system is the spinal nerve root, although any nerve within the peripheral nervous system may become "neuropathic." High amounts of neural traffic course through the spinal nerve, conveying sensory, motor, and autonomic information to its afferent or efferent destination. The spinal nerve is a mixed nerve, formed by the juncture of the dorsal and ventral roots associated with each given spinal cord segment. The dorsal and ventral nerve roots unite to form a spinal nerve at the site where they exit the vertebral canal through the intervertebral foramina. The dorsal root carries somatic and visceral sensory fibers. The ventral root contains alpha and gamma motor neuron fibers. These neurons control muscle contraction and tone. Preganglionic autonomic neuron axons accompany the motor neurons as they egress through the ventral root, but only at those levels of the cord endowed with sympathetic nerve cell bodies in the intermediolateral gray column of the spinal cord (i.e., the thoracic and lumbar levels). The Relationship between Neuropathic and Musculoskeletal Pain Peripheral nerve damage causes altered firing patterns; nerves that are functioning improperly become supersensitive and fire excessively.1 For example, neuropathic nerves often send volleys of discharges to the spinal cord well after the nociceptive input that initiated nerve firing has ended. Healthy nerves, in contrast, stop firing after nociceptive input stops. In other words, one characteristic of neuropathic pain is pain that continues in the absence of ongoing tissue damage. Neuropathic pain is almost always accompanied by muscle shortening and the presence of "tight spots" and/or "trigger points", due in part to the excessive neuronal firing which triggers ongoing muscular contraction. This shortening is palpable as ropy bands within the muscle, and is usually present in groups of muscles that share common innervation patterns, possibly exhibiting dermatomal, myotomal, and sclerotomal relationships. Areas supplied by neuropathic nerves are commonly cooler than normal due to vasoconstriction resulting from sympathetic nervous system hyperactivity. These areas may be edematous from compromised lymphatic and venous drainage. Palpatory findings of tense myofascial tissues, tenderness to palpation, and loss of range of motion signify neural dysfunction. Accompanying features can include autonomic changes and facilitation (also known as "wind-up") of spinal cord segments from which the dysfunctional spinal nerve roots arise. The Significance of Muscle Shortening Muscle shortening causes pain in several ways:
Acupuncture for Neuropathic Pain Muscle shortening is a common denominator of neuropathic pain syndromes. Neuropathic pain affects all structures innervated by the dysfunctional nerve, including joints, muscles, and tendons. Introducing an acupuncture needle into the shortened muscle, and specifically into "trigger points" within muscles, desensitizes the trigger point and alleviates pain. This process of needling tense and painful muscles is known as "intramuscular stimulation", or IMS.1 Performing IMS with an acupuncture needle rather than a hypodermic needle provides a finer degree of stimulation and feedback. The finely tapered point of an acupuncture needle is less traumatic to tissues than a hypodermic needle, and more faithfully transmits the nature and consistency of the tissues penetrated. It provides more refined feedback regarding the "feel" of normal vs. shortened muscles. Normal muscles offer little resistance to the needle as it enters the tissue, while shortened muscles may feel as though they are tensing around the needle, and the tissue may seem "gritty." Occasionally, needle penetration of a shortened muscle may instigate fasciculation, followed soon by relaxation. Tight tissue that does not fasciculate and spontaneously lengthen may require in situ needle placement without manipulation, usually for between ten and twenty minutes. Further needle manipulation, such as rotation or pecking maneuvers may be indicated. Additional approaches may be necessary to relieve tension: electroacupuncture, massage, moist heat, etc. Acute vs. Chronic Problems Pain conditions involving shortened muscles usually respond more rapidly and completely when they are treated soon after onset. Longstanding conditions recruit additional muscles into strain pattern, meaning there are more shortened muscles that require treatment. Chronically shortened muscles often contain fibrotic tissue; response to needling is slower and less dramatic in parallel with the degree of fibrosis.1 Patients with chronic pain problems typically require a longer course and more frequent treatment. In extremely fibrotic regions (e.g., sites of contracture), fibrosis may have displaced nearly all of the striated muscle tissue. In these cases, IMS may not elicit needle-grab (known also as "De Qi" reaction in acupuncture terminology), and this method of treatment may not confer relief of the pain, as the pain may not be the result of contracture.1 Paraspinal Muscle Involvement For fullest resolution of pain problems beyond the spine, IMS of paraspinal muscles corresponding to the myotome supplying neuropathic nerve(s) should accompany local IMS. One may find tender and/or taut bands in paraspinal muscles at the same spinal segmental levels as dysfunctional, more peripheral muscles. IMS of peripheral and paraspinal regions desensitizes both the dorsal and ventral primary rami of the spinal nerve. As such, palpation of the paraspinal muscles and deactivation of trigger zones along the spine is an important component of IMS. Additional Detail IMS treatment requires that a thorough understanding of muscular and neural anatomy. Practitioners should review muscle attachment sites, innervation, and typical pain referral patterns, and have an informed appreciation for the potential risks of treatment, in order to treat patients safely and effectively. Summary Pain in the musculoskeletal system is common, and frequently evades successful and complete resolution by conventional means. The technique of IMS, or trigger point therapy, can provide effective pain relief and may even assist in resolving systemic or autonomic dysfunctions by balancing nerve transmission peripherally and centrally. References 1. Gunn CC. The Gunn Approach to the Treatment of Chronic Pain. Intramuscular Stimulation for Myofascial Pain of Radiculopathic Origin. New York: Churchill Livingstone, 1996. 2. Mense S and Simons DG. Muscle Pain. Understanding Its Nature, Diagnosis, and Treatment. Philadelphia: Lippincott Williams & Wilkins, 2001. 3. Simons D, Travell JG, and Simons LS. Travell & Simons' Myofascial Pain and Dysfunction: The Trigger Point Manual. Volume I. Upper Half of Body. 2nd Edition. Baltimore: Williams & Wilkins, 1999. 4. Travell
JG and Simons DG. Myofascial Pain and Dysfunction. The Trigger Point
Manual. Volume II. The Lower Extremities. Baltimore: Williams &
Wilkins, 1983. Narda G.
Robinson, DO, DVM, DABMA, FAAMA |
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