Radiologia Brasileira - Publicação Científica Oficial do Colégio Brasileiro de Radiologia

 

 

^IPhD, Supervisor of the Technical Team of the Division of Stomatology and Oromaxillofacial Surgery, Hospital Heliópolis - SUS, São Paulo, SP, Brazil
^IIPhD, Professor of Radiology, Department of Imaging Diagnosis - Universidade Federal de São Paulo/Escola Paulista de Medicina (Unifesp/EPM), São Paulo, SP, Brazil

Mailing address

 

 

INTRODUCTION

Systemic sclerosis is a chronic autoimmune inflammatory disease of unknown etiology, characterized by excessive deposition of collagen and glycosaminoglycans in the connective tissue of the skin and internal organs^(1-3). This disease has a low incidence disease, affecting 19 individuals per million inhabitants, with prevalence in women (3:1). The most affected age group is between the third and fifth decade of life⁽²⁾.

Raynaud's phenomenon is usually the first clinical manifestation among several clinical findings such as skin thickening⁽⁴⁾, esophageal dysmotility, restrictive pulmonary disease^(5-7), pulmonary hypertension, arthralgias, myopathies, myocardiopathy, and progressive renal failure^(1-3,8).

Musculoskeletal system involvement is one of the most relevant causes of disability in systemic sclerosis⁽⁹⁾. Frequently, erosion of the intermediate and terminal portions of the phalanges (acroosteolysis) is observed, secondary to the involvement of the fingertips skin. Less frequently, the second and fifth ribs, cervical vertebrae, the distal portion of the clavicle, radius and ulna^(10,11) are affected.

Systemic sclerosis presents characteristic alterations in the maxillomandibular complex, such as thickening of periodontal ligament and areas of osteolysis in the mandible as described by Taveras⁽¹²⁾ in 1959, coinciding with the zones of insertion of the lateral pterygoid, temporal and mainly the masseter muscles. Only a few studies have evaluated the involvement of the masseter muscle in systemic sclerosis as well as the possible association between this involvement and areas of mandibular osteolysis by means of electroneuromyography⁽¹³⁾ and magnetic resonance imaging (MRI)⁽¹⁴⁾. Based on studies on mandible microvascularization, Ramón et al.⁽¹⁵⁾ have proposed that osteolysis originates from muscle ischemia resulting from microvasculopathy typical of systemic sclerosis.

Muscular involvement in systemic sclerosis is probably caused by ischemia, which would lead to an insufficient oxygen and nutrient supply, inflammation, or to the sclerotic process itself. Thus, myopathy would be a primary process of the disease, and not necessarily resulting from the superjacent skin involvement^(16,17). Studies about capillary and arteriolar circulation have shown thickening of the lumen, flow reduction, stenosis and alterations of the capillary architecture⁽¹⁸⁾.

The present study was aimed at evaluating the creatine, choline, lipid and lactate concentrations in the masseter muscle of patients with systemic sclerosis, by means of hydrogen spectroscopy, and correlating the results with the presence of mandibular osteolysis.

 

MATERIALS AND METHODS

The present study included 25 male and female individuals, 15 of them (mean age = 43.72 ± 7.59 years) with diffuse systemic sclerosis, and 10 (mean age = 31.82 ± 12.64 years) without the disease forming a control group. Patients with limited systemic sclerosis or in association with other rheumatic diseases were excluded. The 15 patients with systemic sclerosis were divided into two groups - group I, with seven patients with systemic sclerosis and mandibular osteolysis (Figure 1), and group II, with eight patients with systemic sclerosis without mandibular osteolysis - and the group III included the ten healthy individuals constituting the control group. The present study was approved by the Committee for Ethics in Research, and all the individuals signed a term of free and informed consent.

 

 

All the individuals were submitted to bilateral MRI study of the masseter (Figure 2) in a 1.5 T Sonata^® (Siemens Medical Systems; Erlangen, Germany) equipment with 40 mT gradient. Turbo spin echo (TSE) T2-weighted sequences were acquired with relaxation in the coronal plane, 2810 ms repetition time (TR), 84 ms echo time (TE), number of excitations (NEX) 2, field of view (FOV) of 230 mm and 5 mm interval. T1-weighted sequences were acquired with relaxation in the axial plane (479 ms TR; 13 ms TE; NEX 2; FOV 230 mm; 5 mm interval) with and without fat suppression (420 ms TR; 13 ms TE; NEX 2; FOV 230 mm; 5 mm interval). Total acquisition time was 15 minutes, and total examination time was 25 minutes.

 

 

Magnetic resonance spectroscopy (MRS) with PRESS sequence was performed with a 3D-positioned single voxel. The region of interest (ROI) was represented by a cubic volume visually positioned at the central region of the muscle that anatomically is the site with largest tissue mass (Figure 3). Thus, the frequencies reading was focused exclusively on the masseter muscle, without interferences from surrounding tissues. Values for both masseters were obtained in groups I and II, while in group III, the acquisition was unilateral. Only the metabolites related to the muscle tissue were recorded with the respective frequency scales, in parts per million: creatine (3.14), choline (3.30), lactate (1.14) and lipid (1.42).

The variance analysis (ANOVA) was utilized for statistical analysis of the metabolites creatine, choline, lipid and lactate ratios, followed by the Bonferroni or Tamhane multiple comparisons, as necessary, besides Brown-Forsythe test for equality of groups variance corrections. The adopted rejection level for null hypothesis was 0.10 (10%). The software SPSS 11.5 was utilized for statistical analysis.

 

RESULTS

The values for pure metabolites are listed on Table 1. The analysis of pure metabolites that can be observed on Table 2, demonstrated no significant difference regarding creatine and lipid among the three groups. Regarding choline, no significant difference was observed between patients with and without osteolysis. The lactate concentration was lower in patients with systemic sclerosis, with or without osteolysis, as compared with the healthy individuals.

 

 

The analysis of metabolite ratios demonstrated differences among the groups for creatine/choline, creatine/lactate, lipid/lactate and choline/lipid (Table 3).

 

 

DISCUSSION

MRS was developed early in the nineties, as a noninvasive method for evaluating metabolites concentration in different tissues, such as the brain, heart and muscles⁽¹⁹⁾. This method has been of invaluable help for studying the facial muscles metabolism, considering that conventional methods required biopsies, with great limitations for this type of study⁽²⁰⁾.

Proton magnetic resonance spectroscopy (¹H-MRS) was chosen considering that hydrogen is the most abundant atom in the organism, with higher sensitivity, easy performance and interpretation, besides the capacity to investigate a higher number of metabolites as compared with phosphorus spectroscopy (³¹P-MRS)^(21,22).

In the present study, creatine was the evaluated component of the energy chain. It acts as a creatine kinase substrate transferring the phosphate group of the triphosphate adenosine molecule to creatine for the production of phosphocreatine. Phosphocreatine, on its turn, is the storing compound utilized for energy production during the muscular effort⁽²³⁾. Creatine values were statistically equivalent in the three groups, but a previous study with ¹H-MRS found a higher creatine concentration in the masseter muscle of patients with temporomandibular joint disorder, indicating higher intensity and/or frequency of biochemical reactions necessary for sustaining the muscular function⁽²⁴⁾.

Creatine levels remain stable in the brain tissue in several diseases^(21,23), however this assertion is not valid for the musculoskeletal system, considering that some studies about the energy metabolism in rheumatic diseases have demonstrated variable results. By submitting lower limb muscles to ³¹P-MRS, some studies have observed increased inorganic phosphate/phosphocreatine levels in patients with systemic sclerosis and polymyositis^(15,25), which indicates the presence of ischemic muscle disease. On the other hand, studies with ¹H-MRS have shown a decrease in creatine concentration in the calf of patients with eosinophilia-myalgia syndrome⁽²⁶⁾ and in patients with Duchenne muscular dystrophy⁽²⁷⁾.

As regards to the presence of lactate, the patients with systemic sclerosis presented lower concentration than the healthy individuals. On the other hand, in the present study no difference was observed between patients with and without osteolysis. An in vitro study about muscular metabolism in Duchenne muscular dystrophy has demonstrated a decrease in lactate levels in healthy individuals: the decrease in lactate concentration indicates a reduction of glycolytic activity, or even a decrease in lactate concentration in the muscle⁽²⁷⁾. In the present study, the interpretation of this finding can be based on the assumption that the vascular phenomena related to systemic sclerosis are not reducing the aerobic capacity of the masseter because of the absence of anaerobic glycolysis (lactic acid system), in the same way that there was no change in the energy demand (creatine). So, these phenomena would not significantly act on the masseter, or would act in a partial way, so that the extensive vascular network of the masseter would, in a way, be meeting its oxidative energy needs. Then, both biochemical factors do not appear to significantly contribute to the osteolysis genesis, as observed in the present study.

In the same way as creatine, no significant difference in lipid levels was observed among the three groups. Increased lipid concentration is related to cell degradation and necrosis⁽²¹⁾, and this increase was observed in patients with temporomandibular joint disorder⁽²⁴⁾.

Choline was the only metabolite that showed increased level in healthy individuals. The choline level increase reflects a process of cellular proliferation and evidence of cell membrane synthesis phenomena like those observed in neoplastic diseases, being increased in relation to healthy muscles^(21,28). On the other hand, a decrease in choline levels may demonstrate abnormalities in the membrane, as observed in patients with Duchenne muscular dystrophy⁽²⁷⁾. Increased choline levels may be related to cell proliferation and/or increased density, and besides that, inflammatory processes may also demonstrate peaks of this metabolite resulting from the presence of a large population of inflammatory cells⁽²⁸⁾. Thus, the higher choline concentration in patients with osteolysis may be related to pathophysiological mechanisms that affect the fibroblast in systemic sclerosis⁽²⁹⁾ and to the growth of conjunctive tissue in the epimysium and perimysium⁽¹⁾. Additionally, it was observed that, in systemic sclerosis, one observed that that in systemic sclerosis the tissue hypoxia induces neoangiogenesis and that there is an intense proliferation of the vascular intima layer⁽³⁰⁾. Therefore, increased choline levels may be a product of the above mentioned phenomena, as well as expressing an inflammatory activity in the masseter muscle, with these factors as possible participants in the genesis of osteolysis.

The metabolites ratios were analyzed to evaluate their activity as a whole. The creatine/lipid and choline/lactate ratios were statistically equivalent in the three groups. On the other hand, the other ratios presented variances suggesting significance. Previous studies have showed that choline/ lipid and creatine/lipid ratios are decreased in patients with polymyositis⁽²⁶⁾, while in the present study, an increase was observed in the choline/lipid ratio and absence of variation in the creatine/lipid ratio in patients with systemic sclerosis. Patients with systemic sclerosis also presented lower creatine/choline and lipid/lactate ratios when compared with healthy individuals. As regards creatine/lactate ratio, only the patients without osteolysis showed a decrease in relation to healthy individuals.

Findings at ¹H-MRS should be carefully interpreted, as they may be a consequence of interaction of factors such as the disease activity degree, level of muscle involvement and may even be influenced by medicines such as corticosteroids utilized in the management of the disease⁽²²⁾. On the other hand, this method demonstrates biochemical alterations even in patients with no clinical or morphological evidence of muscle alterations⁽²⁵⁾.

 

CONCLUSIONS

Lower lactate levels were observed in the masseter muscle of patients with systemic sclerosis as compared with healthy individuals, while choline levels tend to be increased in patients with osteolysis. Creatine/choline, creatine/lactate, lipid/lactate and choline/lipid ratios showed a trend towards difference among the groups in the present study. Further studies are necessary to understand the role played by the masseter in the development of mandibular osteolysis.

 

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Mailing address:
Dr. Marcelo Marcucci
Rua Cônego Xavier, 276, sala 200
São Paulo, SP, Brasil, 04231-030
E-mail: marcucci21@gmail.com

Received November 18, 2008. Accepted after revision March 30, 2009.

 

 

* Study developed at the Department of Imaging Diagnosis - Universidade Federal de São Paulo/Escola Paulista de Medicina (Unifesp/EPM), São Paulo, SP, Brazil.