Effect of physical training on the proportion of slow-twitch type I muscle fibers a novel nonimmune-mediated mechanism for muscle impairment in polymyositis or dermatomyositis.код для вставкиСкачать
Arthritis & Rheumatism (Arthritis Care & Research) Vol. 57, No. 7, October 15, 2007, pp 1303–1310 DOI 10.1002/art.22996 © 2007, American College of Rheumatology ORIGINAL ARTICLE Effect of Physical Training on the Proportion of Slow-Twitch Type I Muscle Fibers, a Novel Nonimmune-Mediated Mechanism for Muscle Impairment in Polymyositis or Dermatomyositis MARYAM DASTMALCHI,1 HELENE ALEXANDERSON,1 INGELA LOELL,1 MARCUS STÅHLBERG,2 KRISTIAN BORG,3 INGRID E. LUNDBERG,1 AND MONA ESBJÖRNSSON2 Objective. To compare muscle ﬁber type composition and muscle ﬁber area in patients with chronic polymyositis or dermatomyositis and healthy controls, and to determine whether physical training for 12 weeks could alter these muscle characteristics. Methods. Muscle ﬁber type composition and muscle ﬁber area were investigated by biochemical and immunohistochemistry techniques in repeated muscle biopsy samples obtained from 9 patients with chronic myositis before and after a 12-week exercise program and in healthy controls. Muscle performance was evaluated by the Functional Index (FI) in myositis and by the Short Form 36 (SF-36) quality of life instrument. Results. Before exercise, the proportion of type I ﬁbers was lower (mean ⴞ SD 32% ⴞ 10%) and the proportion of type IIC ﬁbers was higher (3% ⴞ 3%) in patients compared with healthy controls. After exercise, percentage of type I ﬁber increased to 42% ⴞ 13% (P < 0.05), and type IIC decreased to 1% ⴞ 1%. An exercise-induced 20% increase of the mean ﬁber area was also observed. The functional capacity measured by the FI in myositis and the physical functioning subscale of the SF-36 increased signiﬁcantly. Improved physical functioning was positively correlated with the proportion of type I ﬁbers (r ⴝ 0.88, P < 0.01) and type II muscle ﬁber area (r ⴝ 0.70, P < 0.05). Conclusion. Low muscle endurance in chronic polymyositis or dermatomyositis may be related to a low proportion of oxidative, slow-twitch type I ﬁbers. Change in ﬁber type composition and increased muscle ﬁber area may contribute to improved muscle endurance and decreased muscle fatigue after a moderate physical training program. KEY WORDS. Polymyositis; Dermatomyositis; Physical training; Muscle ﬁber; Muscle function. INTRODUCTION Polymyositis and dermatomyositis are chronic inﬂammatory muscle disorders that are clinically characterized by Supported by The Swedish Medical Research Council (2002-74X-14045-02A), The Swedish Rheumatism Association, King Gustaf V’s 80-Year Foundation, Börje Dahlin’s Foundation, Professor Nanna Svartz’ Foundation, and the Karolinska Institutet Foundation. 1 Maryam Dastmalchi, MD, Helene Alexanderson, PhD, Ingela Loell, BSc, Ingrid E. Lundberg, MD, PhD: Karolinska University Hospital, Solna, Karolinska Instituet, Stockholm, Sweden; 2Marcus Ståhlberg, BSc, Mona Esbjörnsson, PhD: Karolinska Instituet, Stockholm, Sweden and Karolinska University Hospital, Huddinge, Sweden; 3Kristian Borg, MD, PhD: Karolinska Institutet, Stockholm, Sweden. Address correspondence to Maryam Dastmalchi, MD, Rheumatology Unit, Karolinska University Hospital, Solna, SE-171 76 Stockholm, Sweden. E-mail: maryam.dastmalchi@ karolinska.se. Submitted for publication May 24, 2006; accepted in revised form March 26, 2007. muscle weakness, particularly low muscle endurance or muscle fatigue mainly in proximal muscles such as thigh, shoulder, and neck muscles (1– 4). Most patients with polymyositis or dermatomyositis experience at least a partial improvement of muscle function with glucocorticoid treatment and other immunosuppressive agents (5). However, many patients are left with longstanding low muscle endurance and reduced quality of life (6,7). The pathophysiologic background to the sustained low muscle endurance and muscle weakness in patients with chronic polymyositis or dermatomyositis is not known. In healthy individuals there is a strong relationship between skeletal muscle function and muscle characteristics such as muscle ﬁber type composition and cross-sectional muscle ﬁber area. Thus, speed of muscle contractions relies mainly on ﬁber type composition and muscle strength on cross-sectional muscle ﬁber area (8 –10). The different ﬁber types, fast- or slow-twitch ﬁbers, are classiﬁed based on their content of contractile proteins, fast or slow myosin heavy-chain (11). The relative frequency of fast- and 1303 1304 Dastmalchi et al Table 1. Summary of patients’ clinical features at ﬁrst biopsy* Patient Diagnosis Age/sex Disease duration, months A B C D DM DM DM DM 44/M 52/F 50/F 59/F 49 44 34 40 E F PM PM 56/F 54/F 102 56 G H I PM PM PM 60/F 56/F 37/F 38 18 44 Treatment Methotrexate 7.5 mg/week 0 Prednisolone 5 mg every second day Prednisolone 3 mg every second day, azathioprine 100 mg/day Azathioprine 50 mg/day Prednisolone 5 mg, azathioprine 100 mg/day 0 Prednisolone 2.5 mg/day Prednisolone 5 mg/day, azathioprine 100 mg/day Duration with prednisolone, years Duration after prednisolone was stopped, years 3 2 3 4 2 2 Ongoing Ongoing 2 3 7 Ongoing 1 1 3 2 Ongoing Ongoing * DM ⫽ dermatomyositis; PM ⫽ polymyositis. Mean age 52 years, median disease duration 44 months. slow-twitch ﬁbers in a muscle determines its functional property with respect to strength/power or endurance capacity. Type I ﬁbers (slow-twitch) contain exclusively slow myosin and possess higher oxidative capacity compared with type IIA and IIB ﬁbers (fast-twitch), which contain fast myosin (12–16). Type IIC ﬁbers are intermediate ﬁbers because they coexpress both fast and slow myosin, can develop into either type I or type II ﬁbers (15,16), and are infrequent in normal adult muscle. Whether patients with chronic dermatomyositis or polymyositis and persistently reduced muscle function possess aberrant muscle ﬁber characteristics that could contribute to the clinical symptoms has not been investigated previously. From this perspective, the reported beneﬁcial effects of exercise in patients with polymyositis or dermatomyositis are interesting (17–21). Until recently exercise was controversial in patients with inﬂammatory myopathies due to fear of exacerbation of muscle inﬂammation. Now several studies have demonstrated that moderate exercise in combination with immunosuppressive therapy is safe and also beneﬁcial to muscle function. The physiologic explanation for the improved muscle function after training in patients with myositis has not yet been addressed. In a recent study, we reported improved muscle endurance with a training program in a group of patients with chronic polymyositis or dermatomyositis (18). These patients were subject to muscle biopsy before and after the exercise program, and these biopsy ﬁndings made it possible for us to address the question of whether molecular changes such as muscle ﬁber characteristics correlated to improved muscle performance. Therefore, the ﬁrst goal of our study was to investigate if muscle ﬁber type composition and muscle ﬁber area were different in patients with chronic polymyositis or dermatomyositis with persisting muscle weakness as compared with age-matched healthy individuals. A second goal was to investigate whether the previously reported improved physical function after a 12-week exercise program was related to any changes in muscle ﬁber characteristics (18). PATIENTS AND METHODS Patients and healthy controls. A total of 8 women and 1 man with chronic polymyositis or dermatomyositis, according to the Bohan and Peter criteria (1,2), who had all participated in a resistive exercise study were included in the present study (18). Two of the original 11 patients were excluded due to insufﬁcient muscle biopsy material. Five patients were classiﬁed as having polymyositis (all women) and 4 as having dermatomyositis (3 women and 1 man) (1). None of the patients had clinical or histopathologic features compatible with inclusion body myositis (22). None had diabetes mellitus or uncontrolled thyroid disease. Clinical and laboratory data have previously been presented in detail (18). Inclusion criteria were as follows: clinically stable; inactive polymyositis or dermatomyositis with a history of remaining muscle weakness; and a duration of immunosuppressive treatment ⱖ12 months, with no change in immunosuppressive therapy during the 3 months before inclusion in the study (18). Inactive disease was deﬁned as absence of inﬂammatory inﬁltrates in muscle biopsy samples and absence of sign of inﬂammation on magnetic resonance imaging (MRI) of thigh muscles. Demographic data and clinical characteristics at the initiation of the study are presented in Table 1. Clinical investigations, muscle biopsy sampling, and MRI were carried out before and after 12 weeks of a physical exercise program (18). The disease was inactive at both investigations as assessed by muscle biopsy samples and MRI. Inﬂammatory inﬁltrates were absent in all biopsy samples but one, in which one small isolated perivascular inﬁltrate was present without any other histopathologic aberrations (18). Muscle tissue from vastus lateralis muscle of 11 healthy individuals, matched for sex (6 women and 5 men, median age 59 years, range 42–78 years), with no clinical symptoms of muscle weakness and normal muscle biopsy results served as controls for analyses of ﬁber type composition and ﬁber cross-sectional area. Due to the limited Muscle Fiber Composition and Training in Polymyositis/Dermatomyositis amount of control muscle tissue from healthy individuals, muscle biopsy specimens from 8 other healthy controls (1 man and 7 women) with a median age of 50 years (range 43– 60 years) were used as control samples for analyses of regeneration markers. All patients and controls gave their informed consent to participate in the study. The study was approved by the local ethics committee at Karolinska University Hospital. Methods. Physical training. The training program used in the present study was based on performing 10 repetitions in several different muscle groups with the intention to improve muscle endurance. Each patient was individually trained to perform a standardized 15-minute home exercise program 5 days a week for 12 weeks followed by a 15-minute walk as previously reported (18). The program contained a warm-up followed by climbing up and down a stool, exercise for shoulder mobility and grip strength with a pulley apparatus, strength exercises for quadriceps and hip muscles, sit-ups without support of the neck, and careful stretching. For those with small or moderate reductions of muscle function, weights (0.25– 2.0 kg) were added as well as upper limb strengthening exercises. Assessments. Muscle function. The Functional Index (FI) in myositis was used for evaluation of muscle strength and muscle endurance (23). The FI is a disease-speciﬁc index comprising 14 functional tests, which include recordings of the maximum numbers of repetitive movements that can be performed in different muscle groups. The FI also includes a recording of the number of observed transfers from side to side and up to a sitting position and peak expiratory ﬂow (23). The FI is scored from 0 (no performance) to 64 (full performance). Perceived health. The Swedish version of the Medical Outcomes Study Short Form 36 (SF-36) was used to evaluate perceived health-related quality of life (24). The SF-36 is a generic, self-administered questionnaire composed of 8 subscales: physical functioning, role physical, bodily pain, general health, vitality, social functioning, role emotional, and mental health. Each subscale is scored from 0 to 100, where 100 indicates good health. Muscle biopsies. Muscle biopsy specimens were obtained from musculus vastus lateralis in the patients, with the second biopsy specimen, after training, obtained from the contralateral side. The specimens were obtained under local anesthesia using a semi-open technique (25). At least 2 tissue samples were taken from each biopsy site. The samples were frozen in isopentane precooled with dry ice and stored at ⫺80°C. All muscle biopsy evaluations were performed on coded slides and the evaluators were blinded to diagnosis as well as order of the biopsy samples. One of the 2 samples from each biopsy site was investigated for presence of histopathologic changes including muscle ﬁber degeneration, regeneration, atrophy, number of ﬁbers with central nuclei, and inﬂammatory inﬁltrates by an experienced neuropathologist. A second 1305 biopsy sample was used for analyses of muscle ﬁber characteristics as described below. Determination of muscle ﬁber type composition and muscle ﬁber cross-sectional area. Histochemical myoﬁbrillar ATPase stainings at pH 4.3, 4.6, and 10.3 were used to classify muscle ﬁbers into type I, IIA, IIB, and IIC subtypes (9,26). The relative number of the different ﬁber types was determined after classiﬁcation of the ﬁber types in ⬃500 ﬁbers in each muscle tissue section. Fiber type characteristics of type I and type II ﬁbers were also determined by a standard immunohistochemistry protocol using monoclonal antibodies directed against different isoforms of myosin: anti-slow myosin heavy-chain antibodies (Clone WB-MHCs; Novocastra, Newcastle, UK) for identiﬁcation of type I ﬁbers and anti-fast myosin heavychain antibodies (Clone MY-32; Sigma, St. Louis, MO) for type II ﬁbers (11,13). In this case the relative numbers of type I and type II ﬁbers were calculated out of ⬃400 ﬁbers depending on the smaller tissue samples with cross-sectional ﬁbers. The validity of the ATPase staining was tested by performing a regression analysis between the type I and type II muscle ﬁber proportion determined by the ATPase staining versus determined by the immunohistochemistry protocol (type I percentage: r2 ⫽ 0.76, P ⬍ 0.05 and type II percentage: r2 ⫽ 0.76, P ⬍ 0.05). Cross-sectional muscle ﬁber areas of type I and type II were established by calculating the mean value out of the individual area of 20 ﬁbers of each ﬁber type per biopsy. This was achieved by applying computerized image analysis (Leica system, BX 60, Tokyo, Japan; digital camera, Sony CDK-500, Tokyo, Japan) from an NADH staining (27). Determination of regenerating ﬁbers. Immunohistochemistry was also used to determine signs of regenerating muscle ﬁbers. We used antibodies toward different markers known to be expressed in different phases of regeneration of the muscle ﬁbers (anti-CD56 antibody [Clone T 199; Dako, Glostrup, Denmark] , anti-vimentin antibody [Clone V9; Dako] , and anti-neonatal myosin heavy-chain antibody [Clone Wb-MHCn; Novocastra] [30,31]) using a standard protocol for immunohistochemistry (32). The whole tissue sections were assessed and the percentage of positively stained ﬁbers per tissue section was estimated. Statistical analysis. Unless otherwise stated, values in the text are the mean ⫾ SD. P values less than 0.05 were accepted as statistically signiﬁcant. Student’s group t-test and Mann-Whitney test were applied to test the difference between groups for the muscle characteristic variables before training (basal). Wilcoxon’s signed rank test for paired observations was applied to test training response for the clinical variables FI and physical functioning in the patient group. Student’s t-test for paired observations was applied to test training response for the different ﬁber types, CD56 percentage, and vimentin percentage. Regarding cross-sectional muscle ﬁber area, a 2-factor analysis of variance (ANOVA; ﬁber type and time) was applied to test the difference between ﬁber type in response to time. 1306 Dastmalchi et al Single regression analyses were applied to determine the relationship between training-induced changes in physical functioning versus training-induced changes in proportion of type I ﬁbers and type II cross-sectional muscle ﬁber area. versus 3.9% ⫾ 2.5%) whereas the percentage of vimentin positive ﬁbers was higher after the training program (0.6% ⫾ 0.9% versus 1% ⫾ 1%; P ⬍ 0.05). The training program did not change the percentage of ﬁbers expressing neonatal myosin heavy-chain. RESULTS Correlations between exercise-induced changes in muscle ﬁber characteristics and clinical performance. A positive correlation was found between increase in physical functioning (a subscale of the SF-36) and increase in the relative proportion of type I ﬁbers in thigh muscles (r ⫽ 0.88, P ⬍ 0.01). A signiﬁcant correlation was also found between increase in physical functioning and increase in type II cross-sectional muscle ﬁber area (r ⫽ 0.70, P ⬍ 0.05). Clinical data. Following the 12-week physical training program, muscle endurance, recorded by the FI score, increased signiﬁcantly (mean ⫾ SD FI score 52 ⫾ 12 before and 58 ⫾ 7 after; P ⬍ 0.05) (Figure 1A). Health-related quality of life as assessed by the SF-36 physical functioning subscale was also signiﬁcantly improved by the exercise program in 8 of 9 patients (mean ⫾ SD 58 ⫾ 19 before and 69 ⫾ 22 after; P ⬍ 0.05) (Figure 1B). The other subscales did not change signiﬁcantly. Muscle characteristics at baseline. Fiber type composition by ATPase staining. At baseline, the relative proportion of type I ﬁbers was signiﬁcantly lower and the relative proportions of type IIB and IIC ﬁbers were higher in patients compared with age-matched controls (Table 2). The relative proportion of type IIA did not differ between the groups. Cross-sectional ﬁber area. In female patients, type I and type II cross-sectional ﬁber area did not differ signiﬁcantly from the female controls (Table 2). The male patient’s cross-sectional muscle ﬁber area of type I and II was within the range of the controls’ muscle ﬁber areas. Muscle ﬁber regeneration. Three markers were used to identify regenerating ﬁbers: CD56, vimentin, and neonatal myosin heavy-chain. At baseline, only a limited number of ﬁbers expressed any of these markers and there was no signiﬁcant difference between patients and controls. CD56 was expressed in 3.4% ⫾ 3.7% of the ﬁbers of the patients and in 3.8% ⫾ 6.0% of the ﬁbers of the healthy controls. The mean ⫾ SD percentage of vimentin positive ﬁbers did not differ between patients and controls (0.6% ⫾ 0.9% and 0.4% ⫾ 0.5%, respectively). The percentage of ﬁbers expressing neonatal myosin heavy-chain was ⬍0.5% in patients as well as in healthy controls. Muscle characteristics after training. Fiber type composition. After the 12-week training program, the relative proportion of type I ﬁbers was 10% higher (P ⬍ 0.05) and the relative proportion of type IIC ﬁbers was 2% lower (P ⬍ 0.05) compared with before the exercise program (Figure 1C and Table 3). The relative proportion of type IIA and IIB ﬁbers did not change with training. Cross-sectional ﬁber area. When applying a repeatedmeasures analysis (ANOVA), a ﬁber type difference was revealed regarding exercise-induced changes in cross-sectional muscle ﬁber area (interaction term: ﬁber type ⫻ time; P ⬍ 0.05) (Figure 1D and Table 3). A 25% increase of type II cross-sectional area (P ⬍ 0.05) was observed, whereas the type I cross-sectional area did not increase signiﬁcantly. Markers of regeneration. The percentage of CD56 positive ﬁbers was unchanged (mean ⫾ SD 3.4% ⫾ 3.7% DISCUSSION To our knowledge, this is the ﬁrst study in which muscle ﬁber characteristics were investigated in patients with chronic polymyositis or dermatomyositis. Two main ﬁndings were observed. First, the patients were found to have a lower proportion of type I ﬁbers and a higher proportion of the intermediate type IIC ﬁbers in comparison with healthy controls. Second, after a 12-week physical training program the ﬁber type composition was closer to normal, the type II muscle ﬁber area had increased, and the changes in ﬁber type characteristics corresponded to clinical improvements in muscle function. Several methodologic precautions were taken to standardize and validate the muscle biopsy data. The muscle biopsy samples were obtained from musculus vastus lateralis, which is classically involved in patients with polymyositis or dermatomyositis and because of its mixed ﬁber type composition, trainability, and accessibility. The control samples were also obtained from the same muscle. Because there are no differences in ﬁber type composition between the 2 legs in healthy individuals, the repeat muscle biopsy was performed on the contralateral muscle to avoid artifacts from the ﬁrst biopsy (33,34). To exclude a side-to-side difference as an explanation for the changed ﬁber type composition after training, a post hoc analysis was performed. This did not reveal any signiﬁcant difference regarding the percentage of type I or type IIC ﬁbers when comparing right and left limbs in pretraining biopsy samples (4 randomly obtained from the right leg and 5 from the left leg) or posttraining biopsy samples, respectively, in our patients. Therefore it is unlikely that a sideto-side difference could explain the observed changes of ﬁber type composition with training. The ATPase technique is well established for ﬁber typing and also allows distinguishing not only between type I and type II muscle ﬁbers, but also between type IIA, IIB, and IIC ﬁbers. The ﬁber type composition was also conﬁrmed by immunohistochemistry. A limitation of the study is the low number of patients; nevertheless, the ﬁber type data and changes with exercise were consistent within the group. The low percentage of oxygen-dependent type I ﬁbers in comparison with healthy controls was unexpected, and there could be several explanations for this ﬁnding. One Muscle Fiber Composition and Training in Polymyositis/Dermatomyositis 1307 Figure 1. Individual changes in patients with chronic myositis after the 12-week exercise program. A, Changes in Functional Index (FI) score. Sixty-four corresponded to the maximal score of the FI. B, Changes in physical functioning, a subscale of the Short Form 36 Health Survey. A score of 100 corresponds to full health. C, Individual changes in the proportion of type I and type IIC ﬁbers. D, Individual changes in muscle ﬁber cross-sectional area of type I and type II ﬁbers (m2). There are missing data for 1 subject in A and B. explanation could be the level of physical activity. Sedentary individuals in general demonstrate a lower proportion of type I ﬁbers compared with physically active individuals (35). However, a sedentary lifestyle seems a less likely explanation, as low physical activity usually is accompa- nied by type II ﬁber atrophy, which was not seen in our patients. Because the controls in our study were healthy individuals with normal physical activity, we also compared the ﬁber type composition with published reference data for healthy, sedentary individuals, and still the pa- 1308 Dastmalchi et al Table 2. Fiber type distribution and ﬁber type areas in vastus lateralis muscle in patients versus controls before training* Patients (n ⴝ 9) Sex, no. Female Male Type I percentage Type IIA percentage Type IIB percentage Type IIC percentage Type I ﬁber area, m2 females Type II ﬁber area, m2 females Type I ﬁber area, m2 males Type II ﬁber area, m2 males Controls (n ⴝ 11) 8 1 32 ⫾ 10 39 ⫾ 12 26 ⫾ 10 3⫾3 4,467 ⫾ 916 6 5 47 ⫾ 16† 35 ⫾ 10 15 ⫾ 14† 1 ⫾ 1† 4,694 ⫾ 1,122‡ 3,538 ⫾ 798 3,441 ⫾ 1,301‡ 5,398§ 4,979 ⫾ 923¶ 4,614§ 4,559 ⫾ 909¶ * Values are the mean ⫾ SD unless otherwise indicated. † Indicates difference between patients and controls at the statistical level of P ⬍ 0.05. ‡ n ⫽ 6. § n ⫽ 1. ¶ n ⫽ 5. tients with myositis had a lower proportion of type I ﬁbers and a higher proportion of type IIC ﬁbers (12,36). Moreover, deconditioning did not affect ﬁber type composition in men with chronic heart failure in comparison with sedentary men when matched for aerobic capacity (37). All together, these observations imply that factors other than low physical activity could contribute to the low proportion of type I ﬁbers in patients with chronic myositis. Effects of glucocorticoids should also be considered, because glucocorticoids are known to affect both ﬁber type composition and ﬁber area, and especially to cause type IIB ﬁber atrophy. All patients in our cohort had been treated with glucocorticoids over several years, and some were still receiving glucocorticoid treatment, although in low doses, at the time of study. However, in patients with rheumatoid arthritis treated with glucocorticoids, a lower percentage of type I ﬁbers (36%) was accompanied by a reduced mean area of both type I and type II ﬁbers, which was not the case in our patients in whom ﬁber area was not decreased (38 – 41). Age and sex are other factors that could explain aberrant muscle ﬁber characteristics, but a decreased percentage of type I ﬁbers has not been reported as a consequence of age, and, moreover, women tend to have an increased oxidative phenotype (42). A possible unexplored explanation for the low percentage of the oxidative type I ﬁbers could be adaptation to muscle tissue hypoxia. This hypothesis is based on previous observations of a reduced number of capillaries. Furthermore, inﬂammation by itself may lead to tissue hypoxia (43). Interestingly, a similar low relative proportion of type I ﬁbers was reported in patients with chronic obstructive lung disease, another condition that gives rise to local tissue hypoxia (44). Further support for local hypoxia in muscle tissue is the demonstration of low levels of ATP and phosphocreatine in muscle observed by magnetic resonance single-photon– emission computed tomography in patients with dermatomyositis or polymyositis indicating a metabolic dysfunction, which could be a consequence of hypoxia (44 – 46). The seemingly contradictory ﬁnding of an increased percentage of type I ﬁbers and at the same time an increased area of type II ﬁbers after training could possibly have 2 explanations. First, considering the extremely low percentage of type I ﬁbers before training, there should be a high potential to increase the percentage of the oxidative ﬁber type exclusively by the fact that the patients trained 5 days a week at 30 minutes per session for 12 weeks. Second, the exercise program consisted of 2 different components regarding ﬁber type recruitment; the ﬁrst component was 15 minutes of strength/weight training in the arms and legs with 10 repetitions and the second component was a 15-minute walk. The ﬁrst part was based on the work load and number of repetitions. The exact load in percentage of 1 voluntary repetition maximum (VRM) was not calculated; however, the training program was deﬁned as ⬃50% of 1 VRM. The increased cross-sectional area of type II ﬁbers and not type I ﬁbers seems reasonable because the training program to some extent included load training, and this type of stimulus is known to increase muscle protein synthesis preferably in type II ﬁbers. In the present study, muscle function improved with physical training and a corresponding increase was recorded in the proportion of oxidative type I ﬁbers and type II cross-sectional area of the thigh muscles. The change in ﬁber type composition resulting from the training program in our study is remarkable, because a change in muscle ﬁber type composition after physical training in healthy individuals is a relatively rare phenomenon (26,47). Muscle ﬁber type characteristics depend on several components including levels of fast or slow myosin heavy-chain Table 3. Distribution of muscle ﬁber type and cross-sectional area in type I and II in patients with chronic myositis before and after training* Before training After training Interaction: type vs time Type I% Type IIA% Type IIB% Type IIC% 32 ⫾ 10† 42 ⫾ 13 39 ⫾ 12 34 ⫾ 11 26 ⫾ 10 26 ⫾ 10 3 ⫾ 3† 1⫾1 * Values are the mean ⫾ SD unless otherwise indicated. † Indicates difference between before and after training at the statistical level of P ⬍ 0.05. Type I area, m2 Type II area, m2 4,570 ⫾ 912 3,658 ⫾ 827† 4,929 ⫾ 1,216 4,555 ⫾ 1,330 P ⬍ 0.05 Muscle Fiber Composition and Training in Polymyositis/Dermatomyositis proteins, volumes of mitochondria, capillary density, and oxidative capacity (48). These characteristics are regulated by a complicated system, which involves multiple signaling pathways and transcription factors (48). The clinical relevance of the changes in ﬁber type composition and ﬁber area was supported by the improvement of physical capacity measured by both the FI test and the reported improvement of physical functioning in the SF-36 questionnaire, which correlated with the increased proportion of type I muscle ﬁbers and the increased type II crosssectional ﬁber area. The mechanisms for the ﬁber type transition induced by exercise in patients with polymyositis and dermatomyositis still need to be determined. From our study we can conclude that it is less likely that the effect on muscle function and on ﬁber type characteristics was due to muscle ﬁber regeneration. A weakness of our study is that we had to include a second cohort of control individuals to compare the number of regenerating ﬁbers with the patient data due to lack of muscle biopsy samples from the ﬁrst healthy control cohort. Nonetheless, we ﬁnd it unlikely that this would have affected our results regarding changes in ﬁber type compositions because only scattered regenerating ﬁbers were seen in the patients’ biopsy samples both before and after exercise, and a similar low frequency was seen in the controls. A possible explanation for the improved function and the adaptation of muscle characteristics could be that exercise improved microcirculation in muscle, lowered total peripheral resistance, and reduced skeletal muscle ischemia, such as has been reported as a result of exercise in patients with chronic heart failure (49). In conclusion, skeletal muscle characteristics that are related to muscle physiology and muscle performance were altered in patients with chronic polymyositis or dermatomyositis with persisting muscle impairment. Whether this is true for patients with myositis in other phases of the disease still needs to be determined. Although the results are based on a small group of patients, we believe that low muscle endurance in patients with chronic myositis could at least in part be explained by a relatively low proportion of oxidative type I ﬁbers. Furthermore, the beneﬁcial clinical effects of physical exercise could at least in part be explained by molecular changes within the skeletal muscle. ACKNOWLEDGMENTS We are grateful to Ylva Friberg and Eva Lindroos for excellent technical assistance with staining procedures, to associate professor Inger Nennesmo for histopathologic evaluation of the muscle biopsy samples, and to associate professor Christer Malm for the handling/delivering of antibodies CD56. We also thank associate professor Ronald Van Vollenhoven for linguistic advice, and professor Lars Klareskog for critically reading the manuscript. AUTHOR CONTRIBUTIONS Dr. Dastmalchi had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. 1309 Study design. Dastmalchi, Lundberg. Acquisition of data. Dastmalchi, Alexanderson, Loell, Borg, Lundberg, Esbjörnsson. Analysis and interpretation of data. Dastmalchi, Alexanderson, Ståhlberg, Borg, Lundberg, Esbjörnsson. Manuscript preparation. Dastmalchi, Alexanderson, Lundberg, Esbjörnsson. Statistical analysis. Dastmalchi, Esbjörnsson. REFERENCES 1. Bohan A, Peter JB. Polymyositis and dermatomyositis (second of two parts). N Engl J Med 1975;292:403–7. 2. Bohan A, Peter JB. Polymyositis and dermatomyositis (ﬁrst of two parts). N Engl J Med 1975;292:344 –7. 3. Dalakas MC. Polymyositis, dermatomyositis and inclusionbody myositis. N Engl J Med 1991;325:1487–98. 4. Plotz PH, Dalakas M, Leff RL, Love LA, Miller FW, Cronin ME. Current concepts in the idiopathic inﬂammatory myopathies: polymyositis, dermatomyositis, and related disorders. Ann Intern Med 1989;111:143–57. 5. Henriksson KG, Sandstedt P. Polymyositis: treatment and prognosis. A study of 107 patients. Acta Neurol Scand 1982; 65:280 –300. 6. Sultan SM, Ioannou Y, Moss K, Isenberg DA. Outcome in patients with idiopathic inﬂammatory myositis: morbidity and mortality. Rheumatology (Oxford) 2002;41:22– 6. 7. Harris-Love MO. Physical activity and disablement in the idiopathic inﬂammatory myopathies. Curr Opin Rheumatol 2003;15:679 –90. 8. Barany M. ATPase activity of myosin correlated with speed of muscle shortening. J Gen Physiol 1967;50 Suppl:197–218. 9. Brooke MH, Kaiser KK. Muscle ﬁber types: how many and what kind? Arch Neurol 1970;23:369 –79. 10. Finer JT, Simmons RM, Spudich JA. Single myosin molecule mechanics: piconewton forces and nanometre steps. Nature 1994;368:113–9. 11. Brooke MH, Kaiser KK. Three “myosin adenosine triphosphatase” systems: the nature of their pH lability and sulfhydryl dependence. J Histochem Cytochem 1970;18:670 –2. 12. Essen B, Jansson E, Henriksson J, Taylor AW, Saltin B. Metabolic characteristics of ﬁbre types in human skeletal muscle. Acta Physiol Scand 1975;95:153– 65. 13. Billeter R, Weber H, Lutz H, Howald H, Eppenberger HM, Jenny E. Myosin types in human skeletal muscle ﬁbers. Histochemistry 1980;65:249 –59. 14. Hintz CS, Coyle EF, Kaiser KK, Chi MM, Lowry OH. Comparison of muscle ﬁber typing by quantitative enzyme assays and by myosin ATPase staining. J Histochem Cytochem 1984;32: 655– 60. 15. Staron RS. Correlation between myoﬁbrillar ATPase activity and myosin heavy chain composition in single human muscle ﬁbers. Histochemistry 1991;96:21– 4. 16. Staron RS. Human skeletal muscle ﬁber types: delineation, development, and distribution. Can J Appl Physiol 1997;22: 307–27. 17. Alexanderson H, Lundberg IE. The role of exercise in the rehabilitation of idiopathic inﬂammatory myopathies [review]. Curr Opin Rheumatol 2005;17:164 –71. 18. Alexanderson H, Stenstrom CH, Lundberg I. Safety of a home exercise programme in patients with polymyositis and dermatomyositis: a pilot study. Rheumatology (Oxford) 1999; 38:608 –11. 19. Alexanderson H, Stenstrom CH, Jenner G, Lundberg I. The safety of a resistive home exercise program in patients with recent onset active polymyositis or dermatomyositis. Scand J Rheumatol 2000;29:295–301. 20. Wiesinger GF, Quittan M, Graninger M, Seeber A, Ebenbichler G, Sturm B, et al. Beneﬁt of 6 months long-term physical training in polymyositis/dermatomyositis patients. Br J Rheumatol 1998;37:1338 – 42. 21. Wiesinger GF, Quittan M, Nuhr M, Volc-Platzer B, Ebenbichler G, Zehetgruber M, et al. Aerobic capacity in adult 1310 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. dermatomyositis/polymyositis patients and healthy controls. Arch Phys Med Rehabil 2000;81:1–5. Griggs RC, Askanas V, DiMauro S, Engel A, Karpati G, Mendell JR, et al. Inclusion body myositis and myopathies. Ann Neurol 1995;38:705–13. Josefson A, Romanus E, Carlsson J. A functional index in myositis. J Rheumatol 1996;23:1380 – 4. Sullivan M, Karlsson J, Ware JE. The Swedish SF-36 Health Survey. I. Evaluation of data quality, scaling assumptions, reliability and construct validity across general populations in Sweden. Soc Sci Med 1995;41:1349 –58. Henriksson KG. “Semi-open” muscle biopsy technique: a simple outpatient procedure. Acta Neurol Scand 1979;59:317–23. Schantz P, Randall-Fox E, Hutchison W, Tyden A, Astrand PO. Muscle ﬁbre type distribution, muscle cross-sectional area and maximal voluntary strength in humans. Acta Physiol Scand 1983;117:219 –26. Novikoff AB, Shin WY, Drucker J. Mitochondrial localization of oxidative enzymes: staining results with two tetrazolium salts. J Biophys Biochem Cytol 1961;9:47– 61. Schubert W, Zimmermann K, Cramer M, Starzinski-Powitz A. Lymphocyte antigen Leu-19 as a molecular marker of regeneration in human skeletal muscle. Proc Natl Acad Sci U S A 1989;86:307–11. Bornemann A, Schmalbruch H. Desmin and vimentin in regenerating muscles. Muscle Nerve 1992;15:14 –20. Fitzsimons RB, Hoh JF. Isomyosins in human type 1 and type 2 skeletal muscle ﬁbres. Biochem J 1981;193:229 –33. Thornell LE, Billeter R, Butler-Browne GS, Eriksson PO, Ringqvist M, Whalen RG. Development of ﬁber types in human fetal muscle: an immunocytochemical study. J Neurol Sci 1984;66:107–15. Ulfgren AK, Lindblad S, Klareskog L, Andersson J, Andersson U. Detection of cytokine producing cells in the synovial membrane from patients with rheumatoid arthritis. Ann Rheum Dis 1995;54:654 – 61. Blomstrand E, Ekblom B. The needle biopsy technique for ﬁbre type determination in human skeletal muscle: a methodological study. Acta Physiol Scand 1982;116:437– 42. Malm C, Nyberg P, Engstrom M, Sjodin B, Lenkei R, Ekblom B, et al. Immunological changes in human skeletal muscle and blood after eccentric exercise and multiple biopsies. J Physiol 2000;529:243– 62. Simoneau JA, Lortie G, Boulay MR, Thibault MC, Theriault G, Bouchard C. Skeletal muscle histochemical and biochemical characteristics in sedentary male and female subjects. Can J Physiol Pharmacol 1985;63:30 –5. Toft I, Lindal S, Bonaa KH, Jenssen T. Quantitative measure- Dastmalchi et al 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. ment of muscle ﬁber composition in a normal population. Muscle Nerve 2003;28:101– 8. Duscha BD, Annex BH, Green HJ, Pippen AM, Kraus WE. Deconditioning fails to explain peripheral skeletal muscle alterations in men with chronic heart failure. J Am Coll Cardiol 2002;39:1170 – 4. Aﬁﬁ AK, Bergman RA. Steroid myopathy: a study of the evolution of the muscle lesion in rabbits. Johns Hopkins Med J 1969;124:66 – 86. Danneskiold-Samsoe B, Grimby G. The inﬂuence of prednisone on the muscle morphology and muscle enzymes in patients with rheumatoid arthritis. Clin Sci (Lond) 1986;71: 693–701. Edstrom L, Nordemar R. Differential changes in type I and type II muscle ﬁbres in rheumatoid arthritis: a biopsy study. Scand J Rheumatol 1974;3:155– 60. Khaleeli AA, Betteridge DJ, Edwards RH, Round JM, Ross EJ. Effect of treatment of Cushing’s syndrome on skeletal muscle structure and function. Clin Endocrinol (Oxford) 1983;19: 547–56. Jansson E. Age-related ﬁber type changes in human skeletal muscle. In: Maughan RJ, Shirreffs SM, editors. Biochemistry of exercise IX. Champaign (IL): Human Kinetics; 1996. p. 297–307. Kissel JT, Mendell JR, Rammohan KW. Microvascular deposition of complement membrane attack complex in dermatomyositis. N Engl J Med 1986;314:329 –34. Hildebrand IL, Sylven C, Esbjornsson M, Hellstrom K, Jansson E. Does chronic hypoxaemia induce transformations of ﬁbre types? Acta Physiol Scand 1991;141:435–9. Park JH, Olsen NJ. Utility of magnetic resonance imaging in the evaluation of patients with inﬂammatory myopathies [review]. Curr Rheumatol Rep 2001;3:334 – 45. Park JH, Vital TL, Ryder NM, Hernanz-Schulman M, Partain CL, Price RR, et al. Magnetic resonance imaging and P-31 magnetic resonance spectroscopy provide unique quantitative data useful in the longitudinal management of patients with dermatomyositis. Arthritis Rheum 1994;37:736 – 46. Jansson E, Esbjornsson M, Holm I, Jacobs I. Increase in the proportion of fast-twitch muscle ﬁbres by sprint training in males. Acta Physiol Scand 1990;140:359 – 63. Spangenburg EE, Booth FW. Molecular regulation of individual skeletal muscle ﬁbre types [review]. Acta Physiol Scand 2003;178:413–24. Gielen S, Adams V, Mobius-Winkler S, Linke A, Erbs S, Yu J, et al. Anti-inﬂammatory effects of exercise training in the skeletal muscle of patients with chronic heart failure. J Am Coll Cardiol 2003;42:861– 8.