P-31 magnetic resonance spectroscopy demonstrates unaltered muscle energy utilization in polymyalgia rheumatica

Polymyalgia rheumatica in 2011

Polymyalgia Rheumatica (PMR) is an inflammatory rheumatic disease that commonly affects individuals over 50 years of age, characterised by pain and morning stiffness of the shoulder and pelvic girdle. PMR can present as 'isolated' form or may be associated with giant cell arteritis. The progress of imaging techniques has helped in understanding different clinical patterns: subclinical vasculitis can occur in at least one-third of PMR patients, causing ischaemic complications. It is considered a polygenic disease and environmental factors may play a role in its pathogenesis, such as viral or bacterial triggers, both in the 'wide' form or assembled with adjuvants in vaccines. The response to steroid therapy is generally dramatic and side effects may occur, as well as the development of glucocorticoid resistance. The optimisation of therapy may require steroid-sparing agents as well as modified-release prednisone as 'nighttime' replacement therapy.

Imaging of polymyalgia rheumatica: indications on its pathogenesis, diagnosis and prognosis

OBJECTIVES

Imaging is one of the most appealing techniques to explore PMR, a disease whose causes, development mechanisms and anatomical targets of inflammatory damage are still scarcely known. This review is concerned with an appraisal of PMR with different imaging modalities with a view to highlighting possible clues to its pathogenesis, diagnosis and prognosis.

METHODS

A systematic literature research was performed searching PubMed until July 2010. The Cochrane Library was searched for the relevant reviews, and the abstracts of the ACR and European League Against Rheumatism congresses of the period 2005-10 were reviewed.

RESULTS

A total of 1059 papers were retrieved, 46 of which were selected at the end of the review process; 6 of them were concerned with two different imaging techniques. Of these papers, 6 (11.5%) were concerned with conventional radiology; 8 (15.4%) with scintigraphy; 17 (32.7%) with ultrasonography (US); 15 (28.8%) with MRI; and 6 (11.5%) with PET. MRI, US and PET appeared to be the most promising imaging techniques. Bilateral subacromial bursitis, biceps long head tenosynovitis and trochanteric bursitis were particularly consistent findings. In addition, MRI and PET showed interspinous bursitis and PET frequently showed large-vessel vasculitis. Few papers have addressed the role of imaging for diagnosis, differential diagnosis and prognosis of PMR.

CONCLUSIONS

Imaging plays an important role in the comprehensive evaluation of PMR, including its pathogenesis, diagnosis and prognosis. Most of its potential is still unexplored, which fact should stimulate further research.

Increased muscle interstitial levels of inflammatory cytokines in polymyalgia rheumatica

OBJECTIVE

Polymyalgia rheumatica (PMR) is characterized by aching of the proximal muscles and increased blood levels of markers of inflammation. Despite the muscle complaints, the current view is that symptoms are caused by inflammation in synovial structures. The purpose of this study was to elucidate the disease mechanisms in symptomatic muscles by measuring interstitial levels of cytokines before and after prednisolone treatment.

METHODS

Twenty glucocorticoid-naive patients newly diagnosed as having PMR and 20 control subjects were studied before and after 14 days of prednisolone therapy (20 mg/day). Interstitial concentrations of interleukin-1α/β (IL-1α/β), IL-1 receptor antagonist, IL-6, IL-8, tumor necrosis factor α (TNFα), and monocyte chemoattractant protein 1 were measured in symptomatic vastus lateralis and trapezius muscles using the microdialysis technique. Plasma levels were measured simultaneously.

RESULTS

Prednisolone abolished symptoms in all of the PMR patients within 1-2 days; the erythrocyte sedimentation rate and C-reactive protein levels were normalized on day 14. In both muscles, interstitial concentrations of all cytokines were markedly higher (P < 0.05) in the PMR patients than in the controls before treatment. In both patients and controls, interstitial levels of most cytokines were higher than plasma levels, with the exception of IL-1α and TNFα, which were lower in both groups. In the PMR patients, interstitial concentrations were normalized after prednisolone treatment.

CONCLUSION

This study introduces a novel view of PMR, indicating that increased interstitial levels of inflammatory cytokines in symptomatic muscles play a role in the pathophysiology of the disease and that cytokines may be released locally. To explore the disease specificity, similar studies in other primary inflammatory conditions are warranted.

[Non-invasive investigation of muscle function using 31P magnetic resonance spectroscopy and 1H MR imaging]

31P MRS and 1H MRI of skeletal muscle have become major new tools allowing a complete non invasive investigation of muscle function both in the clinical setting and in basic research. The comparative analysis of normal and diseased muscle remains a major requirement to further define metabolic events surrounding muscle contraction and the metabolic anomalies underlying pathologies. Also, standardized rest-exercise-recovery protocols for the exploration of muscle metabolism by P-31 MRS in healthy volunteers as well as in patients with intolerance to exercise have been developed. The CRMBM protocol is based on a short-term intense exercise, which is very informative and well accepted by volunteers and patients. Invariant metabolic parameters have been defined to characterize the normal metabolic response to the protocol. Deviations from normality can be directly interpreted in terms of specific pathologies in some favorable cases. This protocol has been applied to more than 4,000 patients and healthy volunteers over a period of 15 years. On the other hand, MRI investigations provide anatomical and functional information from resting and exercising muscle. From a diagnostic point of view, dedicated pulse sequences can be used in order to detect and quantify muscle inflammation, fatty replacement, muscle hyper and hypotrophy. In most cases, MR techniques provide valuable information which has to be processed in conjunction with traditional invasive biochemical, electrophysiological and histoenzymological tests. P-31 MRS has proved particularly useful in the therapeutic follow-up of palliative therapies (coenzyme Q treatment of mitochondriopathies) and in family investigations. It is now an accepted diagnostic tool in the array of tests which are used to characterize muscle disorders in clinical routine. As a research tool, it will keep bringing new information on the physiopathology of muscle diseases in animal models and in humans and should play a role in the metabolic characterization of gene and cell therapy.

[Rhizomelic pseudopolyarthritis: update]

PURPOSE

Update of recent works on polymyalgia rheumatica (PMR). CURRENT KNOWLEDGE ANS KEY POINTS: In polymyalgia rheumatica (PMR) unassociated with giant cell arteritis (GCA) (twice as frequent as GCA without PMR) several recent works demonstrated by MRI or echography that synovitis and/or subacromial bursitis accounted for most of the painful shoulders and could be relieved by steroid injections. Peripheral synovitis can also occur in 10-20% of PMR, and lead to consideration of other diagnoses, mostly RA or the RS3PE syndromes for those cases of PMR with peripheral edema. PMR with asymmetrical onset are often difficult to diagnose early, and the classification criteria for PMR are not widely accepted. When clinical signs suggestive of GCA are lacking, temporal biopsy is positive in only 1 to 5% of PMR cases. Several studies on PMR with so-called 'normal' ESR (below 30 mm, first hour) have cast doubts on the value of this biological sign (although 'normal ESR' should only stand for values below 11 mm). Hence it would be worthwhile to study whether CRP and even SAA deserve to be added to future sets of criteria for PMR. A defect in hypothalamic axis response is often noticed and could play a part in PMR pathogenesis, thus explaining why PMR is quite exclusively noticed after ages 50 or 60. Two-thirds of patients can stop prednisone within 2 years after the onset of treatment. The lack of a prompt response within the first days should suggest differential diagnoses, including some myelodysplastic disorders.

FUTURE PROSPECTS AND PROJECTS

The search for genetic factors common or specific to PMR and GCA could enhance our understanding of these overlapping syndromes. Studies of the transcriptosomes of lymphocytes infiltrating the target tissues (arterial wall in GCA, synovium in PMR) might also prove informative. Controlled studies of new biological treatments like cytokine inhibitors (anti-TNF-alpha, anti-interferon gamma) could demonstrate a clear sparing effect in steroids, a goal not yet achieved by the use of current DMARDs, including MTX.

An additional phase in PCr use during sustained isometric exercise at 30% MVC in the tibialis anterior muscle

The occurrence of an abrupt acceleration in phosphocreatine hydrolysis in the tibial anterior muscle during the last part of a sustained isometric exercise at 30% maximal voluntary contraction until fatigue is demonstrated in seven out of eight healthy subjects by applying in vivo 31P NMR spectroscopy at 1.5 T field strength. This additional third phase in PCr hydrolysis, is preceded by a common biphasic pattern (first fast then slow) in PCr use. The NMR spectra, as localized by a surface coil and improved by proton irradiation, were collected at a time resolution of 16 s. Mean rates of PCr hydrolysis during exercise were -0.44 +/- 0.19% s(-1), -0.07 +/- 0.04% s(-1), and -0.29 +/- 0.10% s(-1) for the three successive phases. The increased rate of PCr hydrolysis, and also the loss of fine force control evident in the force records are consistent with increased involvement of large, fast-fatiguable units later in the contraction.

Impaired redox status and cytochrome c oxidase deficiency in patients with polymyalgia rheumatica

OBJECTIVE

To evaluate redox status and muscular mitochondrial abnormalities in patients with polymyalgia rheumatica (PMR).

METHODS

Prospective evaluation of deltoid muscle biopsy in 15 patients with PMR. Fifteen subjects matched for age and sex, with histologically normal muscle and without clinical evidence of myopathy, were used as controls. Cryostat sections of muscle were processed for conventional dyes, cytochrome c oxidase (COX), usual histochemical reactions, and Sudan black. A total of 300-800 fibres was examined in each case. Blood lactate, pyruvate, and lactate/pyruvate ratio were determined in all patients.

RESULTS

Ragged red fibres were found in eight patients with PMR and accounted for 0-0.5% of fibres. Focal COX deficiency was found in 14 (93%) of 15 patients and in nine (60%) of 15 controls. COX deficient fibres were more common in patients with PMR (range 0-2.5%; mean 0.9%) than in controls (range 0-1.2%; mean 0.3%) (paired t test, p=0.001). Seven (47%) of 15 patients had high blood lactate levels (1.50-2.60 mmol/l) or high blood lactate/pyruvate ratios (22-25).

CONCLUSIONS

PMR is associated with mitochondrial abnormalities not solely related to the aging process.

Insights into muscle diseases gained by phosphorus magnetic resonance spectroscopy

Phosphorus magnetic resonance spectroscopy (P-MRS) has now been used in the investigation of muscle energy metabolism in health and disease for over 15 years. The present review describes the basics of the metabolic observations made by P-MRS including the assumptions and problems associated with the use of this technique. Extramuscular factors, which may affect the P-MRS results, are detailed. The important P-MRS observations in patients with mitochondrial myopathies, including the monitoring of experimental therapies, are emphasized. The findings in other metabolic myopathies (those associated with glycolytic defects or endocrine disturbances) and in the destructive myopathies (the dystrophies and the inflammatory myopathies) are also described. Observations made in normal and abnormal fatigue, fibromyalgia, and malignant hyperthermia are considered. Finally, a summary of the possible diagnostic use of P-MRS in exercise intolerance is provided.

Absence of mitochondrial dysfunction in polymyalgia rheumatica. Evidence based on a simultaneous molecular and biochemical approach

OBJECTIVE

To investigate the molecular and biochemical profile of skeletal muscle mitochondria of patients with isolated polymyalgia rheumatica (PMR).

PATIENTS AND METHODS

We included patients with a recent diagnosis of PMR and as control healthy individuals submitted to orthopedic surgery. Skeletal muscle was obtained from quadriceps, thus was mitochondria immediately isolated. Long polymerase chain reaction and Southern blot transference were performed to detect deleted mtDNA molecules. Mitochondrial oxidative activity using different substrates and individual enzyme activity of respiratory chain complexes were assessed to search for any biochemical dysfunction.

RESULTS

Fifty-one individuals (PMR=25, controls=26) were included. Mean age was 72 (11) years; 45% were females. We found no significant increase of deleted mtDNA molecules in PMR patients compared to controls. Both groups differed neither on oxygen consumption (p=NS for all substrates) nor enzymatic activity (p=NS for all complexes).

CONCLUSIONS

Skeletal muscle mitochondria are molecularly and biochemically unaffected in PMR.

Molecular aspects of magnetic resonance imaging and spectroscopy

Magnetic resonance imaging (MRI) is a well known diagnostic tool in radiology that produces unsurpassed images of the human body, in particular of soft tissue. However, the medical community is often not aware that MRI is an important yet limited segment of magnetic resonance (MR) or nuclear magnetic resonance (NMR) as this method is called in basic science. The tremendous morphological information of MR images sometimes conceal the fact that MR signals in general contain much more information, especially on processes on the molecular level. NMR is successfully used in physics, chemistry, and biology to explore and characterize chemical reactions, molecular conformations, biochemical pathways, solid state material, and many other applications that elucidate invisible characteristics of matter and tissue. In medical applications, knowledge of the molecular background of MRI and in particular MR spectroscopy (MRS) is an inevitable basis to understand molecular phenomenon leading to macroscopic effects visible in diagnostic images or spectra. This review shall provide the necessary background to comprehend molecular aspects of magnetic resonance applications in medicine. An introduction into the physical basics aims at an understanding of some of the molecular mechanisms without extended mathematical treatment. The MR typical terminology is explained such that reading of original MR publications could be facilitated for non-MR experts. Applications in MRI and MRS are intended to illustrate the consequences of molecular effects on images and spectra.

Epidemiology and optimal management of polymyalgia rheumatica

Polymyalgia rheumatica (PMR) is a disease of unknown aetiology that occurs in elderly patients, predominantly affecting the Caucasian population. The disease has a slightly higher prevalence in women than in men. There is ongoing discussion regarding the relationship between PMR and giant cell arteritis; an increasing number of studies indicate that they are closely related. PMR has also been linked with rheumatoid arthritis, myopathy and malignant disease. Oral corticosteroids remain the mainstay of drug therapy for PMR. These drugs usually induce prompt relief of symptoms, and some authors consider this dramatic response to be diagnostic for PMR. However, the ideal initial dosage, the duration of treatment and the optimal tapering schedule are much debated. Other drugs, such as methotrexate and azathioprine, have been suggested as corticosteroid sparing agents. Nonsteroidal anti-inflammatory drugs are generally considered to be unsuitable for the long term treatment of PMR.