Myofascial pain in dogs (Proceedings)

Myofascial Pain is a rarely recognized pain generator for both acute and chronic pain in dogs. It is both defined by and diagnosed by the presence of muscle pain originating from myofascial trigger points (MTrPs) within the muscles.1 Only a handful of articles and conference presentations have addressed MTrPs in dogs, some of which are out of date in regard to current theories and findings accepted in human medicine. A better understanding of Myofascial pain is needed by both the primary care veterinarian and specialist to better manage many commonly seen pain patients.

Writings concerning muscle pain in poeple date back to the 1500's when the French physician Guillaume de Baillou (1538-1616) published "Liber de Rheumatismo" and referred to it as "muscular rheumatism. Thomas Sydenham (1624-1689) considered the "Father of English Medicine" published "Observations Medicae" in 1676 and referred to muscle pain as "Rheumatism". In 1816 the British physician Balfour described "patients as having a large number of nodular tumors and thickenings which were painful to the touch, and from which pains shot to neighboring parts". Numerous other references to muscle pain can be found however most current day knowledge of myofascial pain is based on the works of Janet Travell, MD (1901-1997).

Dr. Travell was a fascinating woman who was both a cardiologist and researcher. Some of her other accomplishments were serving as White House physician to both Presidents Kennedy and Johnson. In her early medical career, Dr. Travell served simultaneously on pulmonary, cardiology and general medical services, in all services she observed, even with dying patients, the major complaint was pain.2 When patients were asked how they were doing they would respond with varying complaints of pain, "I have a terrible pain in my shoulder. I can't sleep. I can't lay on that side." While different medical services would often have explanations for pain none had objective evidence of disease to account for the patient's pain. Dr. Travell, on the other hand, would examine patients and find that all groups had isolated tender spots in the muscles which, when compressed, reproduced the patient's pain. The common problem was myofascial pain syndrome due to myofascial trigger points.

Dr. Travell's observations and research in the area of myofascial pain led to numerous publications and in collaboration with David Simons, MD, wrote Volume 1 Upper Half of Body, Myofascial Pain and Dysfunctions – The Trigger Point Manual in 1983, and Volume 2 Lower half, in 1993. An updated second edition of Volume 1 was released in 1999, two years following the death of Dr. Travell. Review of most every publication regarding myofascial pain in human medicine will show reference to Doctors Travell and Simons' work and publications.

Janssens was perhaps the first to describe MTrPs in dogs in 1991 with his paper describing Myofascial Pain Syndrome in 48 dogs.3 In 1992 he published an additional paper on trigger point therapy.4 In 1999, Frank published a paper using the human model to establish diagnostic criteria in the dog.5 With the exception of these publications and the occasional conference proceedings lecture, little mention of myofascial pain in dogs exists.

The Myofascial Trigger Point

The human model for MTrP can serve, with some exceptions, in the dog. Certain physical features are present in MTrP: 1) an area of exquisite tenderness (localized pain) in a taut muscle band; 2) referred pain elicited by stimulation of the MTrP (referred pain cannot be assessed in the dog); 3) local twitch response (LTR) or contraction of the taut band upon palpation or stimulation; 4) in poeple, reproduction of the patient's spontaneous pain pattern when stimulated; 5) weakness of the muscle without atrophy; 6) restricted range of motion.2

In the dog palpation of the MTrP results in pain and a so-called "Jump Sign" described by Frank.3 The observed response to palpation of the area of exquisite tenderness can vary with the severity of the problem and to some extent the individual. Responses include turning of the head towards the area, attempts to bite, and vocalization, including yelping and growling and efforts to withdraw the affected region or escape. However, the "Jump Sign" described in dogs by Frank and for people in the second edition of Travell & Simons, is not to be confused with a more important diagnostic criteria of local twitch response (LTR).2

Local twitch response (LTR) is described in Travell & Simons as a transient contraction of a group of tense muscle fibers (taut band) that traverse a trigger point. The contraction of the fibers is in response to stimulation of the same trigger point, or sometimes of nearby trigger point. Observation of a LTR is not essential for diagnosis of a MTrP however if present it is considered very significant. Hong considered a LTR as probably the most specific single clinical test of MTrP however it is often difficult to elicit by palpation only.6 In dogs due to hair coat, muscle location (i.e. m. pectineus) and examiner's position in relation to the muscle being examined, LTR may not be observed during evaluation. However, during MTrP therapy with either trigger point dry needling (TrP-DN) or trigger point injection, the LTR becomes both the primary diagnostic criteria as well as validation of correct therapy. Treatment will be discussed later.

Referred pain can only be speculated in the canine patient but could be the explanation for some previous unexplainable findings. Dr. Travell spent years mapping out referred pain patterns in humans and this has become refined to the point that patient description of pain can direct examination to a certain muscle. Significant limitations in communication prevent this type localization in dogs. However, when patient attention to an area (licking, biting, scratching, etc) is noticed without underlying causes determined, referred pain should be a consideration.

Integrated Hypothesis of Trigger Point Formation

To more completely understand the nature of myofascial pain three clinical attributes of MTrP must be understood. The first attribute is myopathic (or endogenous) dysfunction of the muscle that is characterized by a constant and discrete hardness within the muscle referred to as a taut band. The second attribute is a sensory abnormality characterized mainly by pain.

A third is motor dysfunctions that can be local or referred inhibition of the same or other muscles (clinical muscle weakness) or referred spasm in other muscles.7

The true mechanism that leads to the development of a taut band within the muscle is thought to be altered activity of the motor endplate, or neuromuscular junction. Altered biochemical activity at the endplate, increased concentrations of acetylcholine (Ach), changes in Ach receptor (AchR) activity as well as changes in acetylcholinesterase (AchE) are known mechanisms that could explain the dysfunctional endplate. Alterations at the endplate lead to sarcomere contraction within the muscle fibers resulting in the development of the taut band.

Pain is thought to be due to the release of substances from damaged muscle, such as adenosine triphospate (ATP), bradykinin (BK), 5-hydroxytyptamin (5-HT, serotonin), prostaglandins, and potassium. These substances activate muscle nociceptors inducing pain. In myofascial pain syndrome all taut bands are sensitive due to the presence of the MTP within the band. Pain may be spontaneous or only present when stimulated mechanically or metabolically.

Shah et al. showed definitive biomechanical changes within the active MTrP using microdialysis (insertion of a small sampling needle inside an active MTrP).8,9 The milieu sampled from inside the MTrP was found to have significantly increased levels of bradykinin, substance P, IL-1, Tumor Necrosis Factor-α, Calcitonin Gene Related Peptide (CGRP) and serotonin, as well as a lowered pH. The authors showed that unmistakably there were much greater changes of milieu in active MTrP, than latent ones, which explains why active MTrP are so much more painful spontaneously. Additionally, intramuscular hypoperfusion has been clearly demonstrated creating a hypoxic state within the MTrP. Increased levels of CGRP may add to motor endplate abnormalities by increasing the release of ACH from the motor nerve terminal. Noxious stimuli of the muscle nociceptor in damaged muscle results in the release of neuropeptides (Substance P and CGRP) from the nociceptor terminal.

Perpetuating Factors

Muscle nociceptors are activated by noxious stimuli thus starting a cascade of events resulting in the formation of a MTrP within the muscle and subsequent myofascial pain. Understanding precipitating and perpetuating factors in the canine patient that create a noxious stimuli therefore become important in the clinical understanding of myofascial pain and the presence of MTrPs.

     1. Trauma – Contusions, sprains and strains may give rise to MTrPs. Of current interest in human medicine is evidence that supports muscle fiber destruction with eccentric exercise.10,11 Eccentric exercise is defined, as muscle contraction while the muscle unit is lengthening in contrast to concentric exercise; muscle contraction while the muscle unit is shortening.

     2. Chronic repetitive overloading or mechanical overuse of muscles may lead to fatigue and gradual onset of myofascial pain.12 This is the most likely explanation of the development of MTrPs in the canine osteoarthritic patient.

     3. Nerve Root Compression may lead to sensitization of the spinal cord segment resulting in MTrPs in the innervated muscles.13,14

Additional Factors for consideration in canine MPS that evidence supports in human medicine;

• Hypothyroidism and other endocrinopathies are known to cause myofascial pain in people.15

• Visceral-Somatic pain syndromes – Gerwin describes numerous visceral disorders that induce central sensitization and produce myofascial pain, due to MTrPs, regionally in areas innervated by the same spinal cord segments that innervate affected viscera.16 The majority of cells in the dorsal horn of the spinal cord that receive input from the viscera also receive input from receptors in the skin and/or deep tissues. Cardiac disease, gastrointestinal disorders, hepatic and biliary disorder, irritable bowel syndrome and interstitial cystitis are all conditions known to cause myofascial pain and MTrPs in people.

• Nutritional deficiencies – Iron and Folic Acid, in addition to Cobalamin have been described in causing myofascial pain in people.15

Myofascial Examination Techniques

As mentioned previously, the myofascial examination should be combined with a complete physical examination including orthopedic and/or neurologic portions. The purpose of the examination is to identify the presence of a taut band(s) running longitudinally within the muscle and the myofascial trigger point within that band. In larger muscles multiple taut bands maybe present. When the trigger point is found a reaction or "Jump Sign" is usually seen. Active MTrP points can be very painful so gentle examination combined with proper restraint by an assistant are often needed.

The development of palpation skill is essential in locating taut bands and expert instruction maybe of benefit in the beginning to verify findings. Two basic palpation techniques are used to examine muscles, "pincer" and "flat palpation". Both techniques are always done across muscle bellies as to better identify taut bands.

Grasping the muscle belly between the thumb and index finger and applying pressure best describes pincer palpation. Pincer palpation is used to examine muscles like the m. biceps brachii, all portions of the triceps, cranial and caudal muscles of the thigh and ventral cervical muscles. Flat palpation is accomplished by applying pressure directly to the muscle body across muscle fibers with the index and middle fingers. This works on muscle like the m. infraspinatus, m. supraspinatus, m. subscapularis, dorsal cervical, thoracic and lumbar paraspinals, m. latissimus dorsi, m. iliopsoas, gluteals, m. pectineus, etc.

Myofascial Therapy and Treatment Considerations

Numerous therapeutic modalities have been described in the literature for the treatment of MTrPs in people. Therapeutic lasers, extracorporeal shockwave and manual techniques are all described however trigger point dry needling (TrP-DN) and trigger point injections are perhaps the most common therapies offered by trained professionals.17 For purposes of this paper TrP-DN will be discussed.

Trigger point dry needling is performed with an acupuncture needles however dry needling is not to be confused with the selection of specific points located on numerous meridians as in acupuncture. Needle insertion is determined by location of taut band and MTrP. Laser sharp needles such as Seirin J type, Number 5 in 30mm, 40mm and 50mm lengths work exceptionally well due to their ease of insertion.18 Each J type needle is within an insertion tube that aides in initial needle insertion into tissue. Treatment consists of identification of the MTrP within the muscle; placement of the needle in the insertion tube over the MTrP and quickly tapping the needle handle to insert the needle several millimeters into the dermis. The needle is then directed into the area of the MTrP and worked slowly in and out of the muscle without removing the needle completely from the tissues. A local twitch response must be observed or palpated when the MTrP is entered in order to ensure effective treatment. This in and out motion and repeated redirection of the needle is continued until no further local twitch responses are seen.

The microdialysis research by Shah et al., mentioned earlier, showed that abnormalities found within the active MTrP were corrected following LTR. The change in biochemical composition following LTR is the basis for these invasive types of therapy. CGRP levels are reduced following LTR thereby bringing acetylcholinesterase (AchE) activity back to more normal levels. Hypoperfusion and resultant hypoxia are improved and acidic pH is corrected.

The number of treatments required to resolve myofascial pain is entirely based length of time the problem has existed, the number of MTrP and perpetuating factors. MTrP resulting from acute injury maybe be inactivated with one treatment session whereas chronic problems, especially when central sensitization has occurred, may require 4 to 8 sessions.

All clients should be educated in passive stretching exercises of the muscle(s) involved. Application of a form of safe warmth or heat to the treated area may be of benefit in the hours following therapy. In the osteoarthritic patient passive stretching can continue for the remainder of the patient's life.

Conclusions

It is the author's opinion that myofascial pain is a common and treatable cause of pain in dogs though rarely recognized. While literature and research is lacking in veterinary medicine the ever-increasing amount in human medicine should serve as our guide. With the current interest in the management of pain in the canine, myofascial pain must be recognized, documented and discussed.

As veterinary medicine becomes more specialized it becomes easy to focus on only one problem in a single body system rather than the whole patient. Likewise preconceived explanations for pain should never replace complete detailed examination of the entire patient. The veterinary profession should consider Dr. Travell's past words of wisdom to the medical profession.

"In this age of specialization, few clinicians are broad enough to see the whole patient and his/her problem.........understanding with the delicate interplay between patient's mind, body, environment is a paramount importance in helping a patient overcome illness."

Reference:

1 Gerwin RD: Myofascial Pain Syndromes from Trigger Points. Current Pain and Headache Reports 1999, 3: 153-159

2 Travell JG, Simon DG, Simons LS: Myofascial Pain and Dysfunction - The Trigger Point Manual, 2nd Edition, Williams & Wilkins, Baltimore, Maryland 1999

3 Janssens L A: Trigger Points in 48 Dogs with Myofascial Pain Syndromes. Vet Surg 1991 20(4):274-278.

4 Janssens LA: Trigger Point Therapy. Problems in Veterinary Medicine-Vol 4,No.1 March 1992.

5 Frank EM: Myofascial Trigger Point Diagnostic Criteria in the Dog. Journal of Musculoskeletal Pain 1999, 7: No. 1/2: 231-237.

6 Hong CZ: Lidocaine injection versus dry needling to myofascial trigger points: the importance of the local twitch response. Am J Phys med Rehabil 1994, 73(4):256-63.

7 Gerwin RD, Dommerholt J, Shah JP: An Expansion of Simon's Integrated Hypothesis of Trigger Point Formation. Curr Pain Headache Rep 2004, 8 (6):468-75

8 Shah J, Phillips T, Danoff JV, Gerber L: A novel microanalytical technique for assaying soft tissue demonstrates significant quantitative biochemical differences in 3 clinically distinct groups: normal, latent and active. Arch Phy Med Rehabil 2003, 84: A4.

9 Shah J, Danoff J, Desai M, Parikh S, Nakamura L, Phillips T, Gerber L: Biochemicals Associated With Pain and Inflammation are Elevated in Sites Near to and Remote from Active Myofascial Trigger Points . Arch Phys Med Rehabil Vol 89, January 2008: 16-23.

10 Stauber WT, Clarkson PM, Fritz VK, Evans WJ: Extracellular matrix diruption and pain after eccentric muscle action. J Appl Physiol 1990, 69:868-874

11 Proske U, Morgan DL: Muscle damage from eccentric exercise: mechanisms, mechanical signs, adaptation, and clinical applications. J Physio 2001, 537:333-345

12 Borg-Stein J, Simons DG. Focused review: Myofascial pain. Arch Phys Med Rehabil 2002, 83:S40-S47.

13 Hsueh TC, Yu S, Kuan TS, Hong CZ: Association of active Myofascial trigger points and cervical disc lesions. J Formos Med Assoc 1998, 97:174-180.

14 Chu J: Does EMG (dry needling) reduce Myofascial pain symptoms due to cervical nerve root irritation? Electromyogr Clin Neurophysiol 1997, 37:259-272.

15 Gerwin RD: The management of Myofascial pain syndromes. J Musculoskeletal Pain 1993,1, No. 3/4:83-94.

16 Gerwin RD: Myofascial and Visceral Pain Syndromes: Visceral-Somatic Pain Representation. J Musculoskeletal Pain, 10, No. 1/2:165-175.

17 Simunovic Z, Trobonjaca T, Trobonjaca Z: Treatment of medial and lateral epicondylitis - tennis and golfer's elbow-with low level laser therapy: a multicenter double blind, placebo-controlled clinical study on 324 patients. J Clin Laser Med Surg 1998 Jun; 16(3) 145-51.

18 Seirin-America: 234 Libbey Pkwy., Weymouth, MA 02189. (800) 337-9338.