Muscle Changes in RSI: Is the Elephant in the Room?

Different work activities put different stresses and strains on various muscles, tendons, ligaments, and entheses [the so-called muscle-tendon unit] through the body. Certain constrained postures or repetitive or forceful actions may result in injury to these soft tissues resulting in musculoskeletal pain. The resultant problems have specific names according to the type of tissue involved, the location of that tissue and the process causing the symptoms, be it inflammation, degeneration, or direct tissue injury. These problems are generally responsive to standard evidence-based treatments. Sometimes, recurring injury will occur due to the lack of adjustment of ergonomic provoking factors or poor management of the problem in the first place. This is particularly so in muscle groups where myofascial pain syndrome is such a potent and common cause of ongoing peripheral pain generation. None of these conditions are best described as repetitive strain injury [RSI].

In some instances, patients develop more regionalized pain that cannot specifically be attributed to any one of the above conditions. In the first instance, such regional pain may relate to a very localized muscle-tendon tissue damage problem, but as time passes, the clinical features extend beyond that of a local soft-tissue damage problem. The patient with more regionalized pain, particularly in the upper limb, will have pain in the whole of the quadrant to a lesser or greater extent. The main brunt of the pain maybe in any of the hand, wrist, forearm, shoulder girdle, or neck but in general, there is at least some pain in a more regionalized distribution. Other features include widespread abnormal tenderness in the same area, located from the base of the neck, through the front and back of chest wall and into the upper arm that is easily provoked in certain areas, known as tender points, among others. These patients are now generally labeled as having regional pain syndrome given that there is not pain in other parts of the body, the complaints are regionalized and there is no identifiable local peripheral soft-tissue pain generator (1). The term “RSI” appears unhelpful in describing such individuals as soft-tissue injury cannot be demonstrated. Other clinical features include non-anatomical sensory dysesthesia, poor grip strength, co-contraction of muscle groups on examination, subtle swelling of the tissues, and changes in blood flow to the hands. Importantly, many of these patients also have symptoms of varying severity relating to sleep disturbance, fatigue, cognitive change, and a mix of other somatic symptoms that include headache, bowel complaints, or mood change.

In the mid-1980s an epidemic of regional pain syndrome occurred in Australia that was initially termed RSI. As time passed, it was recognized that this term was not a good descriptor of the problem. Initial efforts to change the nomenclature were difficult, but a simple division of RSI into Type 1, indicating all those conditions that might be caused by muscle-tendon pathology and Type 2 being those conditions that essentially comprise regional pain syndrome proved useful to clinicians (1,2). As time passed, the term “regional pain syndrome” became more widely accepted and the recognition that this was a chronic pain syndrome, where there was no underlying tissue damage causing the localized symptoms, became helpful in changing management decisions and work-related health policies, as well as response to the embedded compensation and litigation issues which were present at the time (3).

In this context, other alternative terminology, such as occupational overuse syndrome, cumulative trauma disorder, and work-related upper limb disorder are similarly not helpful as they incorrectly link a putative cause to the problem and incorrectly direct management to peripheral pain generators.

Regional pain syndrome fits somewhere between fibromyalgia syndrome [FMS] and complex regional pain syndrome. It is likely that these pain conditions exist on a spectrum with the common link being central sensitization. Indeed, many patients that were formerly called regional pain syndrome would now fulfill the 2010 American College of Rheumatology clinical diagnostic criteria for FMS (4). These criteria can define three symptomatically painful regions, which in the case of regional pain syndrome of the upper limb would be the neck, upper arm, and lower arm for instance, together with high levels of symptoms which would include poor quality sleep, fatigue, cognitive disturbance, and high levels of other somatic symptoms. As well, many patients with regional pain syndrome will fulfill the evolving criteria for complex regional pain syndrome based on the regionalized complaints of pain, sensory, and muscle dysfunction, and motor change that is seen in many of these patients (5).

In this edition of the Journal of Musculoskeletal Pain, patients with unilateral RSI are identified and shown to have lower oxygenation in the symptomatic arm compared to healthy normal controls and in addition show a shift to the left of the stimulus response curve in a non-symptomatic quadriceps muscle. The patients labeled as having RSI are not well characterized, but if one assumes they do have a regional pain syndrome rather than a disorder of the muscle-tendon unit, such as myofascial pain syndrome or other conditions noted above, then some observations on this new information are possible.

The authors indicate that patients with this condition often have changes in the non-symptomatic opposite limb. This is characteristic of a number of central sensitization problems. Studies have been performed in patients with “whiplash,” where symptoms were prominent in the neck and shoulder girdle area, but abnormalities in quantitative sensory tests such as pain threshold or tolerances, as well as neurophysiological changes, were found in non-symptomatic locations (6). This again highlights the difficultly in using a term such as “whiplash” which links the patient's symptoms to a putative ongoing soft-tissue injury-related cause in a similar fashion to the term RSI. In fact, the authors are identifying the mechanism of central sensitization within such patients. Hence, an alternative diagnostic label is better, again using regional pain syndrome or FMS if patients fulfill the criteria for this disorder. The use of these terms allows access to a wider range of information already established on such conditions and will lead to better management strategies.

In this particular study, the shift to the left in the force-stimulation curve in the non-involved quadriceps muscle does imply that there are central factors operating within the spinal cord or brain. FMS is characterized by such shift to the left in many sensory and other peripheral neural systems allowing increased response to lesser stimuli in a number of organ systems (7). The authors wonder whether this reflects specific changes in Type 2 muscle fibres. Perhaps the changes described in arm oxygenation and “non-involved” thigh muscles reflect effects of central sensitization throughout the body. The study involves small numbers and the patients are not well defined, but the methodology used allows for further exploration of the findings. In particular, changes in central pain-related neural function may be facilitated by these techniques.

A number of chronic pain conditions that appear localized are indeed more systemic. The elephant in the room is usually FMS, or at least the mechanisms that underlie the clinical phenotype of this common pain sensitization syndrome. This FMS elephant also intrudes into a wide range of medical conditions, particularly where pain and distress are prominent. Perhaps 20 percent of such patients have features of FMS (8). It is worth noting that the new American College of Rheumatology criteria allow for a broader appreciation of the background symptoms of patients with persisting regional or widespread pain. Exploration of the so-called “fibromyalgianess” should be part of any clinical assessment and will contribute to a broader view of the patient's illness (9). Identification and consideration of these background central processes allow for the use of strategies that are alternative to those that focus only on peripheral tissue pain generation. This is essential for otherwise difficult-to-treat patients.