Myofascial pain originates from muscles, fasciae and all connective tissues linking them together. In dogs, skeletal muscle accounts for approximately 44 percent of body weight, and up to 57 percent in Greyhounds (Broadhurst, 2019). Despite this, for many years muscle and fasciae were not considered a potential cause of pain in small animals.
Myofascial trigger points (MFTP) characterise myofascial pain. They are often described as firm nodules within a taut band of muscle (Broadhurst, 2019; Formenton et al., 2023; Janssens, 1991; Lam et al., 2024; Langevin, 2021). They are painful on palpation, elicit a characteristic twitch response and can have a referred pain pattern towards distant areas of the body. MFTP can lead to both local motor changes, such as weakness, reduced accuracy of movement and increased muscle fatigue, and autonomic changes, such as piloerection, changes in temperature, flushing, sweating, and so on (Lam et al., 2024). In dogs, changes in the coat patterns have been described (Figure 1) (Broadhurst, 2019).
The myofascial unit
A detailed knowledge of the muscular anatomy of canine and feline patients is a prerequisite to diagnosing myofascial pain. It is beyond the scope of this article to describe the myofascial system, which comprises more than 700 muscles in the dog, all intimately wrapped and connected by fascia (Elbrønd and Schultz, 2015; Myers, 2014).
The functions of fascia are multiple, and include support of the body’s structure and organs, protection, transmission of force, proprioception and coordination. It is thought that 30 percent of the force produced by a muscle is transmitted through the fascia. The fascia ensures that all the muscular units function together as well as glide freely against each other for optimal movement (Broadhurst, 2019; Langevin, 2021; Myers, 2014).
Since all the muscles are interlinked via fascia, a local change in its health, stiffness or shape may affect the whole body
Fasciae are highly innervated fibrous structures (Langevin, 2021). Small deformations in the fascia produce local changes that travel like a wave in a phenomenon called mechanotransduction, changing the shape and chemical properties of the fascia on the way. Since all the muscles are interlinked via fascia, a local change in the health, stiffness or shape may affect the whole body (Elbrønd and Schultz, 2015; Myers, 2014).
Aetiology of myofascial pain and myofascial syndrome
The cause of myofascial trigger points remains unclear. It has been postulated that they may arise from motor end-plate dysfunction and increased release of acetylcholine (Simons et al., 2002). This would lead to a focal area of sustained muscular contraction, followed by local ischaemia, hypoxia and reduced pH. These chemical changes stimulate free nerve endings to produce a nociceptive input. This also alters normal muscular function and induces weakness and movement inaccuracy (Langevin, 2021).
Myofascial pain may be primarily due to fatigue, muscular overload or muscular or fascial injury. When no other underlying condition is diagnosed, this is referred to as myofascial pain syndrome. Primary myofascial pain is described in dogs, with different patterns depending on activity levels, sport or working activity (Formenton et al., 2023; Janssens, 1991). For instance, piriformis syndrome, a condition where the piriformis muscle irritates the ipsilateral sciatic nerve, is well described in humans and has also recently been described in dogs (Toijala et al., 2021).
Myofascial pain may be secondary to underlying painful conditions such as osteoarthritis, spondylosis, nerve damage, and so on. Neurogenic inflammation, chronic inflammation and peripheral sensitisation are among potential causes.
Cases of MFTP due to underlying visceral pain have also been described in humans in a process known as somatovisceral convergence. Abdominal MFTP may remain long after the visceral inflammation has resolved, thus mimicking abdominal pain in the absence of visceral disease (Lam et al., 2024).
Presentation and diagnosis
The prevalence of MFTP in dogs and cats is unknown (Formenton et al., 2023). This may be due to the recent recognition of this condition and the fact that the diagnosis remains purely clinical and few clinicians are trained in recognising it. Objective diagnostic tools such as diagnostic ultrasound, vibration sono-elastography, Doppler flow studies and magnetic resonance elastography have been researched in humans but without clear reliability yet (Janssens, 1991; Lam et al., 2024).
To look for myofascial pain, the clinician should start with a detailed observation of the patient, both dynamic (gait at walk and trot) and static (standing, sitting, lying down). An asymmetry in the posture (Figure 2), a shortened stride and an abnormal tail position may be clues to changes in the myofascial system. A poor response to conventional pain relief drugs, particularly NSAIDs, may be indicative of myofascial pain. The diagnosis is based on detailed rigorous physical examination and palpation, looking for changes in muscle tone, MFTP, restriction in muscular and fascial flexibility, weakness and pain (Formenton et al., 2023; Janssens, 1991). In the author’s experience, a taut band is not always easily identified in small animals. The clinician should also look for underlying causes.
An asymmetry in the posture, a shortened stride and an abnormal tail position may be clues to changes in the myofascial system
Most muscles can be affected by trigger points, although some are more commonly mentioned than others, such as the quadriceps femoris, sartorius, gluteus medius, latissimus dorsi, triceps, pectineus and longissimus (Broadhurst, 2019; Formenton et al., 2023; Janssens, 1991). Interestingly, many trigger points are also described as acupuncture points in Chinese medicine (Myers, 2014; Xiong et al., 2024).
Clinically, two types of MFTP are described:
- Active: very painful on palpation, typical “jump sign”. A clear avoidance reaction and even aggression are displayed (eg trying to bite, hiss, run away). These cause ongoing pain in the absence of palpation
- Latent: only found on palpation. These are non-painful once palpation is stopped, which is more difficult to objectify in animals, who cannot verbalise their pain
In people, research on trigger points has allowed us to map some referring pain patterns. For instance, cervical trigger points may be associated with tension headache, flushing, lacrimation, sweating, temperature changes, dizziness and tinnitus (Lam et al., 2024).
Treatment
The treatment of myofascial pain relies largely on local/locoregional physical therapies. Pharmaceutical intervention is indicated to manage the overall pain burden and is necessary in cases of secondary myofascial pain. For instance, it is common to identify MFTP in the quadriceps and sartorius muscles following stifle osteoarthritis. Direct treatment of MFTP is likely to improve the patient, but this needs to be combined with appropriate pain relief drugs that address the stifle disease, such as NSAIDs. It is beyond the scope of this article to detail pain management drugs.
Skilled manual therapy, potentially combined with acupuncture, is often effective, allowing treatment of the myofascial pain while addressing the associated secondary changes in muscular length and fascial stiffness
Massage, ischaemic compression, dry needling, acupuncture, injection of trigger points with lidocaine and laser therapy may be effective in treating MFTPs (Broadhurst, 2019; Janssens, 1991; Lane and Hill, 2016; Xiong et al., 2024). There is no evidence comparing these therapies in animals. Acupuncture has shown some superiority in human studies (Xiong et al., 2024). Dry needling (insertion of a needle directly into the MFTP) may be effective but is very painful for up to two days after treatment (Broadhurst, 2019; Janssens, 1991; Lam et al., 2024). The author prefers to use other less painful techniques in small animals, particularly as the superiority of dry needling has not been clearly established. From experience, skilled manual therapy, potentially combined with acupuncture, is often effective, allowing treatment of the myofascial pain while addressing the associated secondary changes in muscular length and fascial stiffness (Lane and Hill, 2016).
Once myofascial pain has been treated, a rehabilitation programme comprising a stretching routine and tailored strengthening exercises is recommended. Indeed, myofascial trigger points are usually a symptom of muscular fatigue, overuse or dysfunction, even in the presence of an underlying musculoskeletal or medical condition. Not addressing the perpetuating factors is likely to lead to the recurrence of the MFTP.
Conclusion
Diagnosis and treatment of myofascial pain in small animals is still in its infancy. Myofascial pain treatment needs a multimodal approach, as response to therapy can be variable and patient-dependent. Much research is needed to characterise the condition, underlying causes and best treatment options. Raising veterinary clinicians’ awareness of this disorder, which is likely to be widely underdiagnosed, may help to advance knowledge and promote better patient care and pain management.
