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- PATIENTS AND METHODS
Juvenile dermatomyositis (juvenile DM) is a well recognized but rare pediatric vasculopathy. It is characterized clinically by progressive muscle weakness, initially in the proximal muscles but expanding into the distal muscle groups, and a distinctive rash over the face and extensor surfaces of the limbs (1). The disease may also be systemic, affecting many organs and causing severe morbidity and disability. Severe features of the disease include the development of calcinosis, characterized by the deposition of calcium within tissues, which may cause severe limitations in muscle function and joint mobility as well as severe pain. Calcinosis is believed to be a complication of uncontrolled, active juvenile DM and is related to severe disease (2, 3). At the present time, juvenile DM is diagnosed using the criteria of Bohan and Peter (4), and although these criteria are internationally recognized they are partially outdated because clinical practice has changed and new diagnostic tools, such as magnetic resonance imaging (MRI), have become available. The monitoring of disease activity in juvenile DM remains difficult. Muscle enzyme levels such as creatine kinase (CK) and lactate dehydrogenase (LDH) may be elevated with muscle inflammation, but do not always correlate with disease activity. Changes in muscle strength and function are useful tools to assess disease activity. We have recently shown that inflammation characteristic of active juvenile DM is visible as a high signal intensity on fat suppressed T2-weighted spin echo and STIR MR images (5, 6).
Historically, exercises and muscle strengthening have often been avoided in active juvenile DM. It was believed that exercise may cause muscle fiber damage and inflammation in juvenile DM. Some research does describe the onset of muscle inflammation after exercise, but only after strenuous exercise such as marathon running (7). The degree of inflammation in normal muscle is dependent upon the type, severity, and the duration of the exercise (8).
There has also been concern about the formation of calcinosis in areas of stress within the muscle, which may be related to the amount of exercise. Evidence to support this concept is scarce, and it is now widely believed that calcinosis is a complication of uncontrolled and severe active juvenile DM (3). There are several reports of studies of adults with dermatomyositis and polymyositis that have shown exercise to be beneficial rather than detrimental to these patients, and there is no evidence to support the theory that exercise increases the incidence of calcinosis (9–11).
Very little research has been conducted on children with juvenile DM and their response to exercise, and the few studies that have examined the changes in MRI have not explored the changes in healthy children as a comparison (12). In practical terms, children are very active, and as soon as they are physically able, they start moving and playing after the onset of their juvenile DM, thereby exercising their muscles spontaneously. To our knowledge no treatment center restricts active play for children with juvenile DM. This highlights the inconsistencies of approaches to exercise in this patient population (13).
In considering the safety of an exercise program, the comparison of concentric and eccentric muscle work is important. Concentric muscle work tends to cause less inflammation than eccentric work and it also requires less force in controlling joint movement. Much of the evidence about muscle damage after exercise is based on extreme levels of eccentric exercise, such as marathon running, and is not representative of a prescribed physiotherapy program (8, 14–16).
In a physiotherapy treatment program there are many reasons for performing exercises, including increasing strength and stamina or endurance, as well as increasing neuromuscular coordination and proprioception. Evidence has shown that a combination of eccentric and concentric exercise is the most effective training program for all ages (8, 14, 15, 17–21). This study program was designed to exercise different muscle groups within the thigh, because these are the muscles also being assessed by the MRI and myometer.
This study examines the effects of a specific single bout of moderate exercise on the changes in muscle inflammation of the thigh muscle as measured by MRI T2-weighted relaxation time, muscle strength (measured by myometry), and muscle enzymes (CK and LDH) in children with juvenile DM and healthy children.
- Top of page
- PATIENTS AND METHODS
There have been many concerns about the safety of exercise in the management of juvenile DM, but very few published studies have addressed this issue. This study presents information on the immediate effects of exercise on muscle inflammation in children with juvenile DM compared with the effects in healthy children. It is recognized that the assessment of the degree of muscle inflammation is difficult, but this study uses currently accepted measures of blood serum muscle enzyme levels (CK and LDH), muscle strength, and MRI to assess any changes that may have occurred in response to muscle exercise. The results show that there was no statistically significant change in any of these measures in response to the exercise program in any of the 3 groups of children, except in the assessment of muscle strength of the hip abductors, which showed evidence of fatigue (after exercise) in the healthy children compared with the patients with juvenile DM. This indicates that this physiotherapy-designed exercise program does not immediately increase inflammation assessed at 60 minutes post exercise within the muscles in children with juvenile DM.
For the interpretation of these results, it should be noted that the children with the most severe juvenile DM could not be included in the study. The primary reason for this was that the children with very active disease generally had muscles that were below grade 3 in strength and therefore were unable to undergo myometry and were unable to complete the standardized antigravity exercise program. The exclusion of children with the most active disease does impact the issue of safety of exercise in the treatment of juvenile DM because many professionals are unsure about the treatment for the children with severe active disease. This issue is not directly answered by the study (13).
Open-chain exercises were chosen for the protocol because this type of exercise enables the child to isolate specific muscle groups and specific muscle actions and does not rely upon the weight-bearing capabilities of each child. Also, a previous study (12) used closed-chain exercises only, which are not realistic of a treatment program for children with juvenile DM when used without other types of muscle strengthening techniques.
Muscle inflammation in juvenile DM is patchy, both within the muscle itself and between muscle groups, with anterior muscles thought to be the most common muscle groups affected (32). In this study, it is apparent that the anterior muscle groups in children with juvenile DM as well as healthy children have a higher MRI T2-weighted relaxation time than the posterior and medial muscle groups (Figure 2). Because healthy children have not previously been studied, this difference in the anterior muscles may have been over-interpreted in studies of children with juvenile DM (12).
A previous study reported a change in the MRI after exercise, but this has not been compared with the changes in healthy children before (12). MRI has been shown to measure inflammation in muscle and can provide an assessment of disease activity (5). In this study, there was no statistically significant change in the MRI T2-weighted relaxation time over time in any of the groups and between any of the groups. It is therefore assumed that the changes that did occur did not represent a significant change in inflammation. However, it is also recognized that in assessment of inflammatory response to exercise, a response can be seen up to 48 hours after strenuous exercise. It was not ethically possible to assess the children in this study over a 24-hour period and therefore we do not have data on longer-term changes.
The measurement of muscle force (taken as the myometry scores of muscle strength) is dependent upon many factors, including age and size of the child, cooperation, pain, fatigue, and assessment positioning (33). This effect was minimized by analyzing the change in values. This change in muscle strength represents a change in disease because it is assumed that as inflammation increases, muscle strength or force will decrease; this response can occur over a short period (34). However, a reduction in the myometer scores will also occur if the muscle becomes fatigued and is unable to exert as much force; our results showed that the children with juvenile DM did not fatigue significantly over the study period. This was surprising because inflamed muscles might be expected to fatigue faster than normal muscles. There was a trend in both healthy children and the children in the inactive juvenile DM group to demonstrate an increase in muscle strength over time in all muscle groups except hip abductors. This may be due to an increase in neuromuscular coordination and recruitment of muscle fibers. This effect was not observed to the same degree in the children with active disease. Hip abduction muscles showed evidence of fatiguing in the healthy children but not in the children with juvenile DM. One explanation might be that the children with inactive juvenile DM have a regular home exercise program that works on all muscle groups individually, both eccentrically and concentrically, and that hip abductors are very rarely specifically strengthened in general sports and physical exercise activities in healthy children. Further support for this theory is that unaccustomed eccentric exercise causes rapid-onset muscle weakness and fatigue, yet fatigue does not occur after repeated training has been completed (35). The changes in muscle force described in this study indicate that exercise does not increase muscle inflammation in the short term, and in fact may increase recruitment of muscle fibers and therefore improve muscle function, even in active disease.
The measure of CK and LDH levels is also believed to be a measure of inflammation or muscle damage; however, as other studies have shown, CK and LDH levels are often not an accurate measure of disease activity (2, 36, 37). The LDH and CK levels were not altered by the exercise program applied in this study. However, changes in these measures seen in another study were brought about by strenuous eccentric exercise and occurred between 24 and 48 hours after exercise (8). The exercises performed in our study were not believed to be strenuous or predominantly eccentric, and therefore a delayed response would not be expected. It was also ethically inappropriate in this study to prolong the assessment period of the CK and LDH.
This study begins to address the effect exercise may have on muscles in patients with juvenile DM by assessing the short-term impact that a moderate exercise program has upon the available measures of muscle inflammation. It is important to note that exercise is vital for the repair and growth of muscle, and that lack of exercise and muscle action causes muscle atrophy after a relatively short period of immobility (35). Several studies have also suggested that hypoxia of muscle fibers may have a role in the pathology of juvenile DM and therefore improving circulation to the muscles would be important. Circulation to the muscles is increased by exercise and therefore damage may be decreased if adequate blood and oxygen are supplied to the muscles (38).
Each exercise program should be designed for the individual child, and specific goals need to be identified. During active disease, the aim of treatment should be to maintain muscle length, maintain circulation, and minimize atrophy. Initially this can be achieved by correct positioning of the child and use of active/assisted exercises and by altering the effects of gravity on a muscle group to allow the extremely weak child independent movement and to allow the muscle to function. As disease control is gained by medication, the focus should change to increasing muscle strength and improving muscle endurance. The program should include a combination of concentric muscle work that is progressed by the addition of resistance and moderate eccentric muscle work (39–41). Therefore, we suggest that moderate and controlled combined concentric and eccentric exercise for children with juvenile DM does not increase muscle inflammation. Further research is needed to analyze the longer-term effects of exercise for these children.