Myofascial pain syndrome is a difficult-to-diagnose and seldom-treated condition in dogs. This is despite the fact that it's been a recognized pain issue for more than 400 years and entered mainstream human medicine almost 80 years ago. It's rarely taught in the university setting, and there are no books about it.
The trick of trigger points
Myofascial pain syndrome is always associated with a taut band of muscle fibers within the affected muscle. Multiple trigger points—extremely tender spots—are within these fibers where the myosin and actin have become fixed in the contracted state. This constant contraction can result in both loss of motor function and chronic pain.
The motor component may occur secondary to injury, but, in my experience, it more often is the result of a constant low-grade contraction of the affected muscle. When a muscle is used in slight contraction, fibers always are the first to be put to work and the last to get rest.
We've all experienced this when we try to hold our arms overhead to perform a task. Very quickly it feels as though we're holding a heavy weight; this is because we're using only a few muscle fibers for a simple task, and as those fibers become exhausted, there are no others helping out. The constant contraction eventually causes the working fibers to use all the ATP (energy) required to "un-contract" the muscle. It also puts pressure on local blood vessels, causing a localized ischemia that blocks sources of energy (oxygen-saturated blood) from reaching the affected area when it's needed most. This becomes an insidious pattern resulting in trigger points that can last for many months.
The sensory component of a trigger point can be appreciated by direct palpation of that point. Gentle palpation of the taut band or trigger point often leads to the dog reacting with a jump or with a look toward the side of palpation. More vigorous palpation commonly results in vocalization with a menace and escape response.
Why do animals develop trigger points? Consider an orthopedic procedure or osteoarthritis of the hindlimb. To keep weight off the painful bone or joint, a slight contraction of muscles, such as the iliopsoas, sartorius or rectus femoris, occurs whenever the dog is standing. This protects the painful bone or affected joint but eventually causes trigger points to form. Trigger points usually are multiple and clustered within a muscle. In fact, it's not unusual to final a dozen points in a single muscle.
Diagnosing a trigger point requires practice. The muscle should be gently palpated with a flat hand across the muscle, or in the case of a muscle with large accessible muscle bellies, with a pincer palpation. The key to finding trigger points is to palpate perpendicular to the muscle fibers by using a very gentle technique.
When you encounter a taut band as you move across the muscle, it will feel like a slight thickening that's a little smaller than the diameter of a pencil. If you're unsure if this is a trigger point, use your fingers to apply additional pressure to see if it elicits one of the responses previously mentioned.
The most effective and least expensive treatment for trigger points in dogs is dry needling. Some patients will require sedation and others won't, depending on the level of pain they're experiencing and their personalities.
An acupuncture needle is used to explore the taut band and find the trigger point. When contact with a trigger point is made, an involuntary twitch occurs that involves a spinal reflex loop. This is seen even if the animal is anesthetized. When the contraction is released, the relief experienced by the patient is almost immediate.
The recommended treatment varies depending on the patient and the muscle, but it usually lasts about 20 minutes and is administered weekly until the dog is more comfortable. Not every trigger point is treated, just the ones causing the problem. Trigger points are forever. Once treated, they can remain latent for weeks, months or even years, but all have the potential to become active again.
All veterinary professionals should be familiar with myofascial pain syndrome and how it can negatively impact a dog's recovery from surgery, injury or illness. Fortunately, treatment can be extremely effective in improving the lives of these dogs.
Currently there are no formal training programs to learn how to treat myofascial pain in animals. The International Veterinary Academy of Pain Management will offer a one-day seminar on the topic in association with the 2013 American Animal Hospital Association conference in Phoenix. You also can learn more about trigger-point therapy by contacting the Colorado Veterinary Medical Association/CSU acupuncture program or by visiting Myopain Seminars at myopainseminars.com.
Michael C. Petty, DVM, CCVP, CCRT, is a faculty member of the Canine Rehabilitation Institute, Wellington, Fla., and owner of Arbor Pointe Veterinary Hospital, Canton, Mich.