Have you ever had a patient complain of increased pain post muscle injection? I did. Three of them. With the rise of clinical prediction rules and decision making guidelines, I decided to review the literature for guidance on this matter but the evidence is insufficient . In some cases injections significantly reduce symptoms while in others they only provide a transient, albeit welcome, respite from suffering. I also stumbled upon a few case reports that noted occurrences of isolated neuropathies, infections, tissue necrosis, and even induced psychosis post injections. None of this information proved helpful. So I went back to my cases.
In retrospect, these patients presented with certain commonalities: involvement in cervical acceleration-deceleration injury; positive yellow flags; significant cervical muscle instability; and a subsequent but notable change in pain after injections. Specifically, these patients complained of burning pain after injection. Based on Murphy’s Diagnosis Based Clinical Decision Rule  and Chou’s recent study on predicting disability, these patients had underlying factors that would perpetuate their pain and predispose them to developing chronic pain. I suspect the injections sensitized nociceptors in muscle that had been irritated from de-conditioning after injury. As a result, these patients progressed from nociceptive pain to neuropathic pain and continued into hyperalgesia. According to Smith, in the presence of biopsychosocial factors the neurological phenomenon of sensitization augments aversion to pain, makes pain pre-eminent, and can lead to a regressive trauma experience10. Aversion is a psychological term that encompasses such behaviors as catastrophizing, fear avoidance, and anxiety/depression related to pain. This train of thought provided a useful staring point but lacked a clear direction.
Delving deeper into the body of evidence, one paper showed promise. A paper written this year addressed muscle pain amenable to injection (MPAI). Marcus proposes that not all muscles will respond to injection and the likelihood of a positive response can be attained by a selection algorithm. This is consistent with Staals suggestion that specific subgroups of patients may respond to a specific type of injection therapy 1. Marcus offered a few important suggestions in this paper. First, that the injectate or chemical/material injected is of little importance. Second, that multiple strategic injections through the MTJ and muscle belly induce micro trauma to promote a new phase of healing. This approach is reminiscent of remodeling strategies found in ART and Graston. Marcus determined MPAI by selecting target muscles that elicit pain along the entire length of the muscle from origin to insertion including the musculotendinous junction (MTJ.) This makes sense because the MTJ contains the highest density of mechano- and nociceptors in the muscle. Preceding and following injections, Marcus emphasizes a strict yet simple muscular rehabilitation program. This also makes sense. Murphy tells us that instability is an important perpetuating factor of spinal pain. When stabilizing muscles cannot support the spine, global/primary movers take on the role of stabilizing the spine. I have yet to meet a person that enjoys doing someone else’s job! Apparently, muscles respond similarly. They rebel after misuse, signal the brain and result in neck/head pain. Unless, underlying stability is addressed, muscle and neck pain will continue.
However, these patients presented further challenges. Stability exercises subjectively increased pain initially even though objectively it helped control pain when performed consistently. As a result, patients did not want to perform exercises because they did not think it would help and they preferred passive care. These are common fear avoidance and passive coping behaviors. Lis advises that patients with yellow flags require more attention and increased counseling from the treating doctor to prevent disability. In the care of patients presenting with biopsychosocial factors, Lis recommends reassurance from the doctor that improvement will follow adherence to treatment guidelines, an explanation that hurt does not mean harm, and a focus on stress management techniques to counteract the mind-body connection.
Evidence-based care recommends selecting the best treatment targeted at the primary pain generators, addressing underlying perpetuating factors to thwart chronicity and counseling to squelch a disability mindset early 8,9 10, 12,  . These patients may have benefitted from an evaluation of MPAI early in their care. On one hand, if their muscle pain had not been amenable to injection, this strategy would have prevented the regression of symptoms and provided reassurance that an aggressive rehabilitative program would have helped. On the other hand, had they been suitable candidates for injection, symptom relief would have provided reassurance of improvement and motivation to capitalize on rehabilitative strategies. As we learn, grow, and share clinical best practices our patients will benefit.
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 Chou R, Atlas SJ, Stanos SP, Rosenquist RW. Nonsurgical interventional therapies for low back pain: a review of the evidence for an American Pain Society clinical practice guideline. Spine (Phila Pa 1976). 2009 May 1;34(10):1078-93. Review.
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 Smith, M. Pyschosocial Management of the Patient with Chronic Low Back Pain. NYU Hospital for Joint Disease. Comprehensive Spine Course. NYU Langone Medical Center. Nov 12, 2010.
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