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PubMed2004

Inflammatory disorders of muscle: progress in polymyositis, dermatomyositis and inclusion body myositis.

PURPOSE OF REVIEW: To provide an update on the major advances in inflammatory myopathies. RECENT FINDINGS: Polymyositis is an uncommon disorder that can be misdiagnosed when the old, and never validated, criteria of Bohan and Peter are used. New diagnostic criteria were recently introduced, in which the MHC/CD8 complex is considered a specific immunopathological marker because it distinguishes the antigen-driven inflammatory cells that characterize polymyositis and sporadic inclusion-body myositis from the non-specific, secondary inflammation seen in other disorders, such as dystrophies. In sporadic inclusion-body myositis the inflammatory cells invade non-vacuolated fibers, whereas the vacuolated fibers are not invaded by T cells, implying two independent processes, a primary immune process with antigen-driven T cells identical to polymyositis, and a degenerative process in which beta-amyloid and amyloid-related proteins participate in vacuolar degeneration. In polymyositis and sporadic inclusion-body myositis, antigen-specific and clonally expanded autoinvasive T cells persist for years, even in different muscles, as reconfirmed by proof-of-principle techniques involving CDR3 spectratyping combined with laser microdissected single-cell polymerase chain reaction of the T-cell receptor genes. The formation of immunological synapse between autoinvasive T cells and muscle fibers was recently strengthened by the upregulation of co-stimulatory molecules ICOS/ICOS-L and PD-L1. A new, distinct myopathy characterized by T-cell-triggered macrophage hyperactivation has now been recognized in patients with dermatomyositis-like disease. SUMMARY: Despite recent progress, the antigen(s) responsible for T-cell activation in polymyositis and sporadic inclusion-body myositis and the cause of vacuolar degeneration in sporadic inclusion-body myositis remain unclear. Newer, more aggressive immunotherapies may be encouraging, but control trials are needed to prove efficacy.

Amyloid↗

PubMed2006

Immunogenetic risk and protective factors for the idiopathic inflammatory myopathies: distinct HLA-A, -B, -Cw, -DRB1, and -DQA1 allelic profiles distinguish European American patients with different myositis autoantibodies.

The idiopathic inflammatory myopathies (IIM) are systemic connective tissue diseases defined by chronic muscle inflammation and weakness associated with autoimmunity. We have performed low to high resolution molecular typing to assess the genetic variability of major histocompatibility complex loci (HLA-A, -B, -Cw, -DRB1, and -DQA1) in a large population of European American patients with IIM (n = 571) representing the major myositis autoantibody groups. We established that alleles of the 8.1 ancestral haplotype (8.1 AH) are important risk factors for the development of IIM in patients producing anti-synthetase/anti-Jo-1, -La, -PM/Scl, and -Ro autoantibodies. Moreover, a random forests classification analysis suggested that 8.1 AH-associated alleles B*0801 and DRB1*0301 are the principal HLA risk markers. In addition, we have identified several novel HLA susceptibility factors associated distinctively with particular myositis-specific (MSA) and myositis-associated autoantibody (MAA) groups of the IIM. IIM patients with anti-PL-7 (anti-threonyl-tRNA synthetase) autoantibodies have a unique HLA Class I risk allele, Cw*0304 (pcorr = 0.046), and lack the 8.1 AH markers associated with other anti-synthetase autoantibodies (for example, anti-Jo-1 and anti-PL-12). In addition, HLA-B*5001 and DQA1*0104 are novel potential risk factors among anti-signal recognition particle autoantibody-positive IIM patients (pcorr = 0.024 and p = 0.010, respectively). Among those patients with MAA, HLA DRB1*11 and DQA1*06 alleles were identified as risk factors for myositis patients with anti-Ku (pcorr = 0.041) and anti-La (pcorr = 0.023) autoantibodies, respectively. Amino acid sequence analysis of the HLA DRB1 third hypervariable region identified a consensus motif, 70D (hydrophilic)/71R (basic)/74A (hydrophobic), conferring protection among patients producing anti-synthetase/anti-Jo-1 and -PM/Scl autoantibodies. Together, these data demonstrate that HLA signatures, comprising both risk and protective alleles or motifs, distinguish IIM patients with different myositis autoantibodies and may have diagnostic and pathogenic implications. Variations in associated polymorphisms for these immune response genes may reflect divergent pathogenic mechanisms and/or responses to unique environmental triggers in different groups of subjects resulting in the heterogeneous syndromes of the IIM.

Alleles↗

PubMed2006

Clinical characteristics of patients with myositis and autoantibodies to different fragments of the Mi-2 beta antigen.

OBJECTIVES: To assess the clinical implications of autoantibodies directed against different parts of the Mi-2 beta autoantigen in patients with myositis. METHODS: A systematic assessment of the clinical, laboratory, and histological characteristics of 48 anti-Mi-2 positive patients from six European centres was made. Anti-Mi-2 autoantibodies were determined with an ELISA using four overlapping fragments spanning the entire amino acid sequence of the autoantigen. Data were compared with results for a large group of anti-Mi-2 negative patients with myositis published previously. RESULTS: Anti-Mi-2 autoantibodies were found in dermatomyositis, polymyositis, and inclusion body myositis. In general, myositis with anti-Mi-2 autoantibodies was characterised by relatively mild disease, sometimes accompanied by extra-muscular symptoms, including arthralgia, arthritis, Raynaud's phenomenon, and interstitial lung disease. Cardiac disease was not seen, and treatment response was fair. No differences were found between patients with autoantibodies to different fragments of the Mi-2 beta antigen, except for a potentially increased risk of cancer in patients with antibodies directed to the N-terminal fragment of the autoantigen. CONCLUSIONS: Anti-Mi-2 autoantibodies are not a marker of a specific subtype of myositis. No significant differences between patients with autoantibodies to different fragments of the Mi-2 beta autoantigen are found, with the possible exception of an increased risk of cancer in patients with antibodies to the N-terminal fragment.

Adenosine Triphosphatases↗

PubMed2001

Autoantibody profiles in the sera of European patients with myositis.

OBJECTIVE: To determine the prevalence of myositis specific autoantibodies (MSAs) and several myositis associated autoantibodies (MAAs) in a large group of patients with myositis. METHODS: A total of 417 patients with myositis from 11 European countries (198 patients with polymyositis (PM), 181 with dermatomyositis (DM), and 38 with inclusion body myositis (IBM)) were serologically analysed by immunoblot, enzyme linked immunosorbent assay (ELISA) and/or immunoprecipitation. RESULTS: Autoantibodies were found in 232 sera (56%), including 157 samples (38%) which contained MSAs. The most commonly detected MSA was anti-Jo-1 (18%). Other anti-synthetase, anti-Mi-2, and anti-SRP autoantibodies were found in 3%, 14%, and 5% of the sera, respectively. A relatively high number of anti-Mi-2 positive PM sera were found (9% of PM sera). The most commonly detected MAA was anti-Ro52 (25%). Anti-PM/Scl-100, anti-PM/Scl-75, anti-Mas, anti-Ro60, anti-La, and anti-U1 snRNP autoantibodies were present in 6%, 3%, 2%, 4%, 5%, and 6% of the sera, respectively. Remarkable associations were noticed between anti-Ro52 and anti-Jo-1 autoantibodies and, in a few sera, also between anti-Jo-1 and anti-SRP or anti-Mi-2 autoantibodies. CONCLUSIONS: The incidence of most of the tested autoantibody activities in this large group of European patients is in agreement with similar studies of Japanese and American patients. The relatively high number of PM sera with anti-Mi-2 reactivity may be explained by the use of multiple recombinant fragments spanning the complete antigen. Furthermore, our data show that some sera may contain more than one type of MSA and confirm the strong association of anti-Ro52 with anti-Jo-1 reactivity.

Antibody Specificity↗

PubMedDate not supplied

Nodular sarcoid myositis of skeletal muscle diagnosed by fine needle aspiration biopsy. A case report.

BACKGROUND: Symptomatic striated muscle involvement in sarcoidosis is rare. Muscle biopsy is usually required for the diagnosis. Fine needle aspiration biopsy (FNAB) has been successfully used in diagnosing soft tissue lesions. To the best of our knowledge, FNAB of sarcoid myositis has not been reported. CASE: A 31-year-old, black female with a history of sarcoidosis presented with an enlarging, painful, left calf mass. Infected thrombi were suspected. FNAB showed numerous loosely arranged epithelioid histiocytes, multinucleated giant cells and skeletal muscle cells. The overall cytologic picture was that of granulomatous myositis. The cytologic features coupled with the patient's history and magnetic resonance imaging findings suggested sarcoid myositis. Subsequent muscle biopsy showing noncaseating granulomata and negative stains for organisms confirmed the diagnosis of nodular sarcoid myositis. CONCLUSION: Nodular sarcoid myositis can be suggested by FNAB cytology in a patient with a past history of sarcoidosis.

Adult↗

PubMed1989

Elevated IgG antibody to Sarcocystis cruzi associated with eosinophilic myositis in cattle.

Blood sera, skeletal muscle, and cardiac muscle from 24 bovine carcasses condemned for eosinophilic myositis by US Department of Agriculture meat inspection veterinarians were compared with similar specimens from 35 random carcasses passed for human consumption. Fluorescence values determined by using a fluorometric immunoassay system were used to measure the specific antibodies to Sarcocystis cruzi. The values were significantly elevated in carcasses condemned for eosinophilic myositis as compared to carcasses passed for human consumption. The elevated fluorescence values appeared to be more than coincidental, suggesting that S. cruzi may be a causative agent of eosinophilic myositis. Microscopic examination of affected muscle revealed lesions typical of eosinophilic myositis. Lesions were characterized by extensive multifocal areas of myofiber hyaline degeneration, necrosis with sarcoplasmic fragmentation, mineralization of occasional myofibers, and atrophy of fibers with varied stages of fibrosis. Inflammatory cell exudates were predominantly eosinophils, with some macrophages and lymphocytes, and extravasated erythrocytes within, and adjacent to, affected myofibers. Affected muscles contained more S. cruzi than unaffected muscle from passed carcasses. However, a distinct cause and effect relationship could not be determined between the parasite and the presence of eosinophilic myositis.

Animals↗

PubMed1991

Myositis ossificans: MR appearance with radiologic-pathologic correlation.

We reviewed retrospectively the MR images of eight histologically proved cases of myositis ossificans and correlated the MR appearance with the histologic findings, as well as with other radiologic studies. Patients with available MR images were chosen from a group of 326 cases in our radiologic archives of histologically proved and radiologically correlated myositis ossificans. In addition to MR images, all patients had plain radiographs, six had CT scans, and two had arteriograms. On T2-weighted spin-echo MR, the lesions were relatively well defined and inhomogeneous and had intermediate to high signal intensity. The latter corresponded to a central proliferating core of fibroblasts and myofibroblasts with a myxoid stroma resembling nodular fasciitis, rimmed by osteoblasts with bone production. Edema surrounded lesions less than a few months old. T1-weighted images of early lesions were normal or showed evidence of a mass by displacement of fat planes. Hemorrhage and fluid-fluid levels were seen in one lesion of intermediate duration. Mature lesions tended to be well defined with inhomogeneous signal intensity, similar to that of fat, representing areas of fat situated between bone trabeculae within the lesion. We present the MR appearance of myositis ossificans and correlate it with other radiologic studies and the histologic findings. The varying appearance of myositis ossificans relates to the histologic changes that occur as the disorder progresses. Knowledge of the MR appearance of myositis ossificans is important in that the lesion has many of the MR imaging characteristics frequently associated with malignancy.

Adolescent↗

PubMed1991

Anti-Jo-1 autoantibodies and the immunopathogenesis of autoimmune myositis.

Polymyositis and dermatomyositis are inflammatory myopathies characterized by proximal muscle weakness and myopathic electromyographic and histological findings. While the causes of myositis are not known, the close association of these disorders with a spectrum of autoantibodies suggests an etiologic and/or pathogenetic role for autoimmune processes. Of particular interest in this regard are antibodies directed against histidyl as well as other tRNA synthetases which are almost uniquely associated with myositis and may define a distinct subset of patients. Recently we isolated the histidyl tRNA synthetase gene which encodes the autoantigen representing the most frequent target of the myositis autoimmune response. The isolation and expression of this gene has allowed us to investigate both the autoreactive epitopes on histidyl-tRNA synthetase and the extent to which these correlate with functional epitopes on the molecule. As described here, the results of these studies as well as other recent data pertaining to the immunopathogenesis of myositis, provide a framework for delineating the mechanisms which render synthetases and other translation-related proteins autoantigenic in myositis, and allow one to examine the significance of such autoimmune responses in the etiology and pathogenesis of inflammatory myopathy.

Autoantibodies↗

PubMed1992

Inclusion body myositis: analysis of 32 cases.

Inclusion body myositis is characterized by an insidious onset, progressive indolent course, and is generally felt to be refractory to standard therapy for myositis. We reviewed the charts of 32 patients with muscle biopsy findings suggestive of inclusion body myositis. The average time from symptom onset to diagnosis was 37 months, but initially 40% were incorrectly diagnosed. Twenty-eight patients (88%) were classified as definite or probable inclusion body myositis and were treated with various combinations of prednisone and immunosuppressive agents. Sixty-eight percent of those treated experienced a decrement in function and muscle strength. Three patients exhibited longterm improvement while 12 patients experienced delayed progression, defined by short term improvement in strength or a stable functional class, All of these patients received therapy, 5 in the form of methotrexate and prednisone. All untreated patients deteriorated clinically. In summary, (1) inclusion body myositis is a clinically distinct entity which is frequently misdiagnosed initially. (2) While clinical improvement with therapy is rare, our observations support recent reports that therapy may be associated with a slower rate of clinical progression. (3) Optimal therapy remains uncertain, but the use of low dose methotrexate and prednisone may warrant further study.

Adult↗

PubMed1991

A reexamination of the relationship between myositis and malignancy.

The association between myositis and malignancy has long been appreciated. However, several recent reviews question the validity of this connection and the utility of pursuing an extensive search for occult malignancy in myositis. We report 9 patients fulfilling diagnostic criteria for myositis seen in the past 12 years. In each, a neoplasm was uncovered only in the course of a systematic search or, when initial investigation was deferred, at a later time. Of the 9 patients, 6 had dermatomyositis, 3 polymyositis. In 3 cases, solid tumors were diagnosed concomitantly with the myositis. In the remaining 6 patients, an advanced neoplasm was detected in the course of followup. In retrospect, some of these tumors might have been detected at an earlier and perhaps more treatable stage had a more rigorous initial malignancy search been pursued. Based on this experience, it is imperative that the clinician undertake a more exhaustive search for occult malignancy in patients with myositis than is currently recommended.

Adult↗

PubMed1982

Myositis ossificans: radiologic evaluation of two cases with diagnostic computed tomograms.

Although most physicians associated myositis ossificans with recent, acute trauma, only 40%-60% of patients give such a history. The appearance of a soft tissue mass without a clear history of trauma may suggest a diagnosis of sarcoma, especially because results of a biopsy of the central portion of an area of myositis ossificans may yield immature, undifferentiated tissue resembling a sarcoma. Pain and rapid growth of a mass are more usual in myositis ossificans than in sarcomas, and careful inquiry may reveal stretching injury or chronic trauma associated with normal, vigorous, physical activities. Recognizing the characteristic histologic zoning phenomenon (immature tissue centrally surrounded by more mature tissue and a peripheral shell of benign bone) during the biopsy procedure permits the correct diagnosis of myositis ossificans. Plain radiographs or conventional tomograms may reflect this histologic zoning by demonstrating the typical, mature, outer shell of bone. Although additional radiographic studies are not usually necessary, they may be obtained when the mass is suspected to be a sarcoma. In two patients computed tomographic scans clearly demonstrated well-defined, peripheral shells of mature bone, diagnostic of myositis ossificans.

Adolescent↗

PubMed1995

Nitric oxide production in relation to spontaneous B-cell lymphoma and myositis in SJL mice.

SJL mice spontaneously develop B cell lymphomas (historically described as reticulum cell sarcomas) by 12 months of age and inflammatory muscle disease (myositis) by 6 months of age. Tumors originate in mesenteric lymph nodes and in Peyer's patches and resemble human germinal center lymphomas. The growth of reticulum cell sarcomas is completely dependent on cytokine production by normal T cells. The spontaneous myositis, which resembles human idiopathic myositis, is characterized by various abnormalities in skeletal muscle, including infiltration with inflammatory cells consisting primarily of macrophages. The participation of different cytokines in the pathogenesis of the lymphoma and the massive invasion of macrophages into muscle tissues led us to investigate the possible involvement of nitric oxide (NO.), which is known to be synthesized by activated macrophages under inflammatory conditions. Elevated NO. production, measured by urinary nitrate excretion, by SJL mice in comparison with BALB/c control mice was observed as early as 7 weeks of age. Both aging and degree of spontaneous myositis correlated with increased nitric oxide production. Oral administration of N-monomethyl-L-arginine, an inhibitor of nitric oxide synthase (NOS), reduced urinary nitrate excretion and also the severity of myositis. Immunohistochemical analysis revealed the presence of inducible NOS (iNOS) in cells in the spleen, lymph nodes, and skeletal muscle. The iNOS is primarily responsible for the enhanced nitric oxide production. Morphology of cells that stained positive for iNOS was similar to that of macrophages infiltrating into the affected tissues. Chronic production of elevated amounts of nitric oxide by the SJL mice, therefore, provides a useful in vivo model for future studies of cellular damage resulting from endogenously produced NO.in combination with oxygen radicals.

Amino Acid Oxidoreductases↗

PubMed1994

Necrotizing fasciitis and myositis caused by group A streptococci. Epidemiology, diagnosis, and treatment of "flesh-eating bacteria".

Despite the absence of conclusive proof, the incidence of necrotizing fasciitis and myositis due to GAS may be increasing, possibly related to shifts in the proportion of GAS isolates of M-Types 1 and 3. These M-types (or the production of exotoxins and proteases associated with them) may lead to severe GAS infections in individuals who lack immunity. Recent television and newspaper reports underscore the potential virulence of GAS even in young and previously well individuals although they do this at the expense of raising fear in the general population. It is unfortunate that these reports often fail to emphasize the rarity with which GAS causes myositis and fasciitis. The overall incidence of these dreadful diseases is very low. In fact, by extrapolating the CDC estimates, we suspect that only 14-40 cases of GAS-induced myositis or fasciitis occur annually in North Carolina. Each of these infections is a true calamity for the affected patients and their physicians, but together they represent only a tiny fraction of all GAS infections that occur in North Carolinians each year. It is relatively easy to separate uncomplicated streptococcal cellulitis from GAS-induced fasciitis and/or myositis by bedside exam and old-fashioned clinical judgment. Prompt and aggressive surgical debridement and antibiotic therapy are needed for all patients with myositis and/or fasciitis due to GAS; others can be treated with simple beta-lactam antibiotics and careful observation.

Anti-Bacterial Agents↗

PubMed1994

Myositis in primary Sjögren's syndrome. Report of 3 cases.

OBJECTIVE: To describe the findings and course of myositis in primary Sjögren's syndrome (SS). METHODS: We studied myositis in SS when clinically indicated. Of 104 patients with SS, we identified 3 cases. In all, the diagnosis was made according to clinical data, biochemical, electromyographic and biopsy criteria. Other autoimmune diseases were excluded. RESULTS: We found a prevalence of 3% of myositis secondary to SS. There were no significant associations between myositis and other clinical or laboratory variables. CONCLUSION: Although rare, myositis must be considered a part of the spectrum of SS. In our experience, treatment with steroids and immunosuppressive drugs was successful.

Adult↗

PubMed2002

Outcome in patients with idiopathic inflammatory myositis: morbidity and mortality.

OBJECTIVE: To assess the long-term outcome of a cohort of 46 patients with idiopathic myositis by assessing both health status, as measured by the SF-36, and cumulative survival probability over a 20-yr follow-up period at a single rheumatology centre. Methods and results. Forty-six patients under long-term follow-up from 1978 to 1999 were identified from our database. All patients fulfilled three out of four of the Bohan and Peter criteria for myositis. We excluded those with malignancy-associated disease and those with inclusion body myositis. Twenty-three patients (50%) had adult-onset polymyositis, 14 (30.4%) had adult-onset dermatomyositis, one had childhood-onset dermatomyositis and eight (17.4%) had an overlap syndrome (associated with either systemic lupus erythematosus or rheumatoid arthritis). During the course of the disease, seven patients (15.2%) went into full remission, eight (17.4%) had monophasic illness, nine (19.6%) had a relapsing-remitting course, 16 (34.8%) had chronic progressive illness and six (13.04%) died. All patients had significantly lower SF-36 scores in all aspects of health compared with the general population (P< or =0.001). Patients with chronic progressive illness had significantly greater bodily pain (P< or =0.05, t-test) than those with a relapsing-remitting illness, but did not differ in other aspects of health. There was no significant difference in the scores in the different domains of the SF-36 between the patients with active disease and those with inactive disease (0.05<P<0.1). Six of the 46 patients died. Cumulative survival probability was calculated. The five-year survival rate was 95% and the 10-yr survival rate 83.8%. CONCLUSION: Patients with myositis report significantly poorer health compared with the general population. Health status and disease activity are important outcome measures in the assessment of patients with myositis.

Adult↗

PubMed1993

New advances in inclusion-body myositis.

The major new advances in seeking the pathogenic mechanisms of sporadic inclusion-body myositis and hereditary inclusion-body myopathy are discussed. Hypotheses are presented regarding the possible causes and significance of amyloid deposits in sporadic inclusion-body myositis and the roles of abnormally accumulated ubiquitin, beta-amyloid protein, beta-amyloid precursor protein, alpha 1-antichymotrypsin, hyperphosphorylated tau, and prion protein in the vacuolated muscle fibers in both sporadic inclusion-body myositis and hereditary inclusion-body myopathy. Because hereditary inclusion-body myopathy is virtually free of Congophilic amyloid deposits but, like sporadic inclusion-body myositis, contains large accumulations of beta-amyloid protein, it is possible that the lesions in hereditary inclusion-body myopathy may represent "early" changes. There are striking similarities between the pathology of inclusion-body myositis muscle and brains affected by Alzheimer's disease in regard to accumulation of ubiquitin, beta-amyloid protein and its precursor protein, alpha 1-antichymotrypsin, and hyperphosphorylated tau.

Amyloid↗

PubMed2002

Neutrophilic myositis: an extra-intestinal manifestation of ulcerative colitis.

Myositis of the skeletal muscle is rarely seen as an extraintestinal manifestation of inflammatory bowel disease. We report a case of a 36-year-old man with ulcerative colitis who developed 3 episodes of steroid responsive myositis in a 4-month period. He presented with a blistering rash followed by pain and massive swelling in the right shoulder and lower extremities, with marked elevation in muscle enzymes. Diagnosis of myositis was made after a muscle biopsy, which showed neutrophilic infiltrate in the deep subcutaneous tissue and skeletal muscle. Review of the literature indicates only a few cases of myositis associated with ulcerative colitis, most of them during an acute exacerbation of the disease. However, the present patient had his first episode when the ulcerative colitis was in remission. Myositis in ulcerative colitis may present atypically, in particular mimicking pyomyositis. Clinicians should be aware of this unusual steroid-sensitive complication.

Journal Article↗

PubMed1996

Mechanisms of lysis by activated cytotoxic cells expressing perforin and granzyme-B genes and the protein TIA-1 in muscle biopsies of myositis.

OBJECTIVE: Polymyositis (PM) and cermatomyositis (DM) are inflammatory muscle diseases of autoimmune origin. A chronic mononuclear cell infiltrate is always present around PM and DM muscle damage. In PM, the predominant cells are activated cytotoxic cells, natural killer, and CD8+ T lymphocytes. Cytotoxic cells can kill the target cells via 2 mechanisms. Both pathways induce target cell death by releasing the molecules (granule exocytosis) perforin (PF), which attacks the target cell membrane and causes cell death by necrosis, and TIA-1 protein and granzyme-B (GZB), possibly responsible for apoptosis. We studied the mechanisms of lysis in muscle biopsies of myositis. METHODS: We used a panel of monoclonal antibodies to determine the phenotypes of reactive lymphocyte subsets, in situ hybridization to study the expression of PF and GZB genes, and immunohistochemistry to evaluate TIA-1 protein production in muscle biopsies from 14 patients with myositis (11 PM/3 DM). Results were compared to those obtained from muscle biopsies of 12 control patients with muscle weakness, including patients with muscle dystrophy and vasculitis, but without myositis. RESULTS: Abundant CD8+ cells, especially in endomysial sites in PM, formed the predominant phenotype. The predominant mononuclear cells observed in DM were CD4+ T cells and CD22+ B lymphocytes, in perivascular sites. The GZB and PF genes and the TIA-1 protein were expressed simultaneously in muscle samples from patients with myositis. GZB, PF, and TIA-1 positive cells were predominantly located in endomysial sites of PM, in the nonnecrotic muscle fibers. In DM, these positive cells were rare. CONCLUSION: In myositis, especially PM, cytotoxic cells may cause muscle damage and muscle cell necrosis and/or apoptosis by releasing several proteins (PF, GZB, and TIA-1 proteins) responsible for the lysis of these stimulating target cells. Some drugs (prednisone and cyclosporine) inhibit the release of GZB and PF. Their efficacy may be due in part to this inhibitory effect.

Adult↗