THE RELATIONSHIP OF INFECTIOUS AGENTS TO INFLAMMATORY MYOSITIS

TNF-Alpha in the Locomotor System beyond Joints: High Degree of Involvement in Myositis in a Rabbit Model

The importance of TNF-alpha in arthritis is well documented. It may be that TNF-alpha is also markedly involved in muscle inflammation (myositis). An animal model where this can be investigated is needed. A newly developed rabbit myositis model involving pronounced muscle overuse and local injections of substances having proinflammatory effects was therefore used in the present study. The aim was to investigate the patterns of TNF-alpha expression in the developing myositis and to evaluate the usefulness of this myositis model for further TNF-alpha research. Human rheumatoid arthritis (RA) synovial tissue was examined as a reference. TNF-alpha immunoexpression and TNF-alpha mRNA, visualized via in situ hybridization, were detected in cells in the inflammatory infiltrates of the affected muscle (soleus muscle). Coexistence of TNF-alpha and CD68 immunoreactions was noted, suggesting that the TNF-alpha reactive cells are macrophages. Expression of TNF-alpha mRNA was also noted in muscle fibers and blood vessel walls in areas with inflammation. These findings demonstrate that TNF-alpha is highly involved in the myositis process. The model can be used in further studies evaluating the importance of TNF-alpha in developing myositis.

Syrian hamster infected with Leishmania infantum: a new experimental model for inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are inflammatory disorders of unknown origin. On the basis of clinical, histopathological, and immunological features, they can be differentiated into three major and distinct subsets: dermatomyositis; polymyositis; and inclusion-body myositis. Although a few animal models for IIM are currently available, they lack several characteristic aspects of IIMs. The aim of our study was to examine skeletal muscle involvement in an experimental animal model of visceral leishmaniasis, a disseminated infection caused by the protozoan parasite Leishmania infantum, and to compare features of associated inflammation with those of human IIM. Syrian hamsters infected intraperitoneally with amastigotes of L. infantum were killed at 3 or 4 months post-infection, and the skeletal muscles were studied. Focal inflammation was predominantly observed in the endomysium and, to a lesser extent, in perivascular areas. Degenerating muscle fibers were also found, as well as myonecrosis. Immunofluorescence with confocal laser scanning microscopy was used to characterize the phenotype of inflammatory infiltrates and the distribution of MHC class I and II in muscle biopsies. The infiltrating inflammatory cells consisted mainly of T cells, and CD8(+) T cells were found in non-necrotic muscle fibers that expressed MHC class I on the sarcolemma. In addition to T cells, several macrophages were present. The model we are proposing closely resembles polymyositis and may be useful in studying certain aspects of this disease such as the role of T cells in muscle inflammation and myocytotoxicity, while also providing novel therapeutic targets.

Genetic and environmental risk factors for idiopathic inflammatory myopathies

Although the studies discussed are beginning to reveal a number of genetic and possible environmental risk factors for myositis, further investigations are needed to fully understand and classify these syndromes. The difficulties in this process include small numbers of subjects with varying disease phenotypes available for study, polygenic risk factors for which it remains unclear which are primary and which are secondary or linked genes, and the lack of validated environmental exposure assessment tools. New technologies and international collaborative approaches, however, may overcome some of these difficulties and allow us to identify genetic and environmental risk factors, as well as the critical gene-environment interactions in the IIM and its subgroups. Nonetheless, our understanding of these diseases is still in the early stages. Although we have learned a great deal about these disorders through detailed investigations over the last several decades, we have even further to go to understand the environmental triggers and genetic susceptibilities for the myositis syndromes.

Severe acquired toxoplasmosis in immunocompetent adult patients in French Guiana

The most common presentation of symptomatic postnatally acquired toxoplasmosis in immunocompetent patients is painless cervical adenopathy. Acute visceral manifestations are associated in rare cases. We report 16 cases of severe primary toxoplasmosis diagnosed in French Guiana during a 6.5-year period. All of the subjects were immunocompetent adults hospitalized with clinical presentations consisting of a marked, nonspecific infectious syndrome accompanied by an altered general status with at least one visceral localization, mainly pulmonary involvement (14 cases). Acute toxoplasmosis was diagnosed according to the results of serological tests suggestive of recent primary infection and the absence of an alternative etiology. Recovery was rapid following specific antitoxoplasmosis treatment. Thirteen of the 16 patients had consumed game in the 2 weeks before the onset of the symptoms, and in eight cases the game was considered to have been undercooked. Toxoplasma strains, which were virulent in mice, were isolated from three patients. Microsatellite analysis showed that all of these isolates exhibited an atypical multilocus genotype, with one allele found only for isolates of this region.

Congenital inflammatory myopathy: a demonstrative case and proposed diagnostic classification

There have been few reports of congenital inflammatory myopathy in the literature, and most of these have been associated with congenital muscular dystrophy. We review the literature and present a case with electromyographic and muscle biopsy evidence of congenital inflammatory myopathy with onset in the perinatal period and no evidence of a congenital muscular dystrophy. There was evidence of subjective improvement following corticosteroid administration (approximately 1 mg/kg per day) with a concomitant normalization of the serum creatine kinase activity. Of particular interest in the case was the history of maternal infection, suggesting a possible postinfectious molecular mimicry as the etiology of the muscle inflammation. This case suggests that a rare form of congenital inflammatory myopathy does exist that is not associated with a congenital muscular dystrophy. A preliminary classification scheme is proposed to separate true congenital cases from those acquired after birth and those cases associated with congenital dystrophy.

Multinodular polymyositis in a patient with human immunodeficiency and hepatitis C virus coinfection

We report a patient who developed multiple inflammatory muscle masses and generalized polymyositis in the setting of combined human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infection. Magnetic resonance imaging (MRI) of muscles showed patchy edema which was particularly intense within the nodular masses. Polymerase chain reaction (PCR) showed no evidence of either virus within muscle. This report reviews earlier literature on muscle nodules associated with myositis and discusses the differential diagnosis of muscle masses in HIV infection.

HIV infection-associated inflammatory musculoskeletal disorders

Inflammatory musculoskeletal complaints are relatively common during the course of HIV infection, although they tend to be more frequent during late stages. The clinical spectrum is varied, ranging from arthralgias to distinct rheumatic disorders, such as Reiter's syndrome and psoriatic arthritis. The therapeutic management often poses a challenge, although most patients respond to conventional first- and second-line anti-inflammatory medications.

Idiopathic inflammatory myopathies

Dermatomyositis, polymyositis, and inclusion body myositis are the major categories of idiopathic inflammatory myopathy. These inflammatory myopathies are distinct clinically, histologically, and pathogenically. Features of dermatomyositis and polymyositis can overlap with those of other autoimmune connective tissue diseases. In this article, the authors review the characteristic features of these myopathies, update the recent developments in this area, and provide a framework for treatment.