Describing and expanding the clinical phenotype of anti-MDA5-associated rapidly progressive interstitial lung disease: case series of nine Canadian patients and literature review.

OBJECTIVE: To describe and expand the phenotype of anti-MDA5-associated rapidly progressive interstitial lung disease (MDA5-RPILD) in Canadian patients. METHOD: All proven cases of MDA5-RPILD hospitalized in the University of Montreal's affiliated centres from 2004 to 2015 were selected for inclusion. RESULTS: Of nine consecutive patients, RPILD was the presenting manifestation in seven, whereas two patients developed RPILD 2 years after the onset of arthritis and of chronic interstitial lung disease. In the case with arthritis, RPILD was probably triggered by initiation of tumour necrosis factor-α-inhibitor therapy. In most patients (89%), RPILD was accompanied by concomitant onset of palmar/lateral finger papules, skin ulcerations, and/or mechanic's hands. All patients experienced profound weight loss over 1-2 months (mean ± SD 10.2 ± 4.8 kg). All had arthralgias and/or arthritis. Six patients were clinically amyopathic; only one patient had creatine kinase (CK) levels > 500 U/L. Initial ferritin and transaminase levels were elevated in 86% and 67% of patients, respectively. The antinuclear antibody (ANA) test was negative for nuclear and cytoplasmic staining; antisynthetase autoantibodies were negative. Three patients died; time from initial symptoms to death ranged from 7 to 15 weeks. All six survivors received mycophenolate mofetil and/or tacrolimus as part of induction and/or maintenance therapy. CONCLUSION: In an inpatient setting, RPILD associated with characteristic skin rashes, profound weight loss, articular symptoms, normal or low CK with elevated ferritin, and absent fluorescence on ANA testing should alert the clinician to the possibility of MDA5-RPILD. T-cell-mediated therapies may play a role in this highly lethal condition.

Reaction of anti-OJ autoantibodies with components of the multi-enzyme complex of aminoacyl-tRNA synthetases in addition to isoleucyl-tRNA synthetase.

Autoantibodies to five aminoacyl-tRNA synthetases have been reported, and all have been associated with a syndrome of myositis and interstitial lung disease. Four of these synthetases exist free in the cytoplasm, but the fifth, isoleucyl-tRNA synthetase (recognized by anti-OJ autoantibodies), is a component of the multi-enzyme complex containing at least seven synthetases. In an effort to better understand the origins of these antibodies, we examined sera from 11 patients with anti-OJ autoantibodies for evidence of reaction with other components of the complex. All sera showed a characteristic pattern of 10 proteins bands by immunoprecipitation from HeLa cell extract. 10 of 11 sera significantly inhibited isoleucyl-tRNA synthetase enzyme activity. Serum and IgG from four patients also inhibited leucyl-tRNA synthetase activity, and serum and IgG from two inhibited lysyl-tRNA synthetase. Immunoblotting experiments supported reaction of the two sera with lysyl-tRNA synthetase, and revealed additional reactivity of three sera with a 160-kD component believed to be glutaminyl-tRNA synthetase. Despite reaction of some sera with additional synthetases, the immunoprecipitated tRNA appeared the same with all sera, and functioned as tRNA(ile). While reaction with more than one synthetase was seen with some anti-OJ sera, all synthetases targeted by anti-OJ sera were components of the complex, rather than unassociated synthetases. These findings suggest that an initial autoantibody response against isoleucyl-tRNA synthetase was followed by extension to involve other components of the synthetase complex. These observations may have implications for understanding the generation of antisynthetase autoantibodies.

Anti-KJ: a new antibody associated with the syndrome of polymyositis and interstitial lung disease.

Antibodies to aminoacyl-tRNA synthetases (anti-Jo-1, anti-PL-7, anti-PL-12) have been found in the serum of some patients with polymyositis (PM). Patients with these antibodies have an unusually high rate of interstitial lung disease (ILD) in association with their PM. Two patients (K.J. and B.T.) with severe ILD and PM were found to have antibodies to a cytoplasmic antigen, but tests to determine whether the antigen was an aminoacyl-tRNA synthetase were negative, including tests of KJ serum for inhibitory effects on the 20 synthetases. KJ immunoprecipitates did not contain tRNA, in contrast to antisynthetase sera. When IgG samples were added to a reticulocyte in vitro translation system at a concentration of 0.3 mg/ml, KJ IgG inhibited globin mRNA translation by 98%, while anti-Jo-1 IgG inhibited 62% and normal IgG had little effect. Thus, both anti-KJ and the antisynthetases are directed at antigens that are involved in translation and protein synthesis, and both are associated with the syndrome of lung disease and PM. This syndrome may be associated with antibodies to translation-related proteins in general, which may have implications for the link of PM and enteroviruses, which are mRNA viruses.

Cloning of a complementary DNA coding for the 100-kD antigenic protein of the PM-Scl autoantigen.

Anti-PM-Scl antibodies are associated with polymyositis-scleroderma overlap or either disease alone. Among sera from 39 patients with anti-PM-Scl, 23 recognized the 100-kD band in immunoblot against HeLa cell extract, 16 of which also stained the 70-kD band. A human thymocyte lambda gt11 cDNA expression library was screened with anti-PM-Scl serum, and two clones were identified whose products reacted with 33 and 37 of 39 anti-PM-Scl sera, respectively, but none of 26 negative control sera. Affinity-purified antibody reacting specifically with plaques of the clone stained the 100-kD band on immunoblot, reacted with nucleoli of HEp-2 cells, and immunoprecipitated the PM-Scl protein complex. Partial sequences of both inserts were identical. One insert was fully sequenced, and additional 5' and 3' sequence was obtained using a gene-specific primer to form a cDNA with HeLa cell RNA as template followed by PCR. The complete nucleotide sequence included 2,739-bp coding for a predicted full-length protein of 98,088 D. There was no homology with the PM-Scl 75-kD protein and no significant homology with other proteins. A mixed-charge cluster was identified, with 22 charged amino acids of 37. In conclusion, the full-length cDNA sequence was determined coding for the PM-Scl 100-kD protein, the most commonly antigenic protein of the PM-Scl complex.

Molecular analysis of a major antigenic region of the 240-kD protein of Mi-2 autoantigen.

Anti-Mi-2 autoantibody is strongly associated with dermatomyositis and found in sera of 20% of patients. Mi-2 antigen contains at least eight components and previous evidence suggested that the 240-kD protein was the antigenic component for at least some sera. In this study, anti-M-2 patient sera were used to screen human thymocyte and HeLa cell lambda gt11 expression libraries, and two clones from each had plaques specifically reactive with anti-Mi-2 sera. Studies with affinity-purified antibody supported the identification of the clones. All of 44 anti-Mi-2 sera reacted with the plaques, but none of 44 control sera reacted significantly. The cDNAs were identical, and full sequencing of one revealed an open reading frame spanning a 1,054-bp insert. Rescreening the library with the cDNA yielded a 1,589-bp cDNA that continued the open reading frame. The Mi-2 cDNA hybridized to a single 7.5-8.0 kb mRNA of HeLa cells, by Northern blot. Rabbit antiserum directed at a portion of the cDNA product reacted with HeLa 240-kD Mi-2 protein. The sequence was notable for four potential zinc-fingers and several charged regions. The protein encoded by the cDNA produced in vitro reacted with only one of five of the Mi-2 sera. These findings indicate that the Mi-2 240 kD is a novel protein that is antigenic for all Mi-2 sera, and strongly suggests that a major common epitope is conformational in nature.

Humoral immunity in polymyositis/dermatomyositis.

Autoantibodies are found in most patients with polymyositis (PM) or dermatomyositis (DM) and 35-40% of these patients have myositis-specific antibodies. Twenty-five to thirty percent have anti-aminoacyl-tRNA synthetases, of which anti-Jo-1, directed at histidyl-tRNA synthetase, is by far the most common. Patients with anti-synthetases have a high frequency of myositis, interstitial lung disease, Raynaud's phenomenon, and other features constituting an "anti-synthetase syndrome." Anti-synthetases tend to react with conformational epitopes and to inhibit enzymatic activity, suggesting reaction with conserved regions. Sera with antibodies to alanyl-tRNA synthetase (anti-PL-12) also have antibodies to tRNA(ala), whereas most sera with other anti-synthetases do not react directly with tRNA. Production of the antibodies appears to be antigen-driven, and is influenced by HLA genes, although an initiating factor, possibly a viral infection, may be important. Antibodies to other cytoplasmic antigens, most notably the signal recognition particle (anti-SRP), are seen in a small percentage of patients. Patients with anti-SRP do not tend to develop the anti-synthetase syndrome, but may have very severe disease. Antibodies to the nuclear antigen Mi-2 are also specific for myositis, and are strongly associated with DM. Several autoantibodies, including anti-PM-Scl, anti-Ku, and anti-U1 and U2 RNP, have been associated with scleroderma-PM overlap. The role of humoral immunity in the myositis of PM and DM has not yet been clarified. Capillary loss and ischemic damage are important in DM, and seem to be mediated by humoral mechanisms, whereas cell-mediated attack on muscle fibers is important in PM. The mechanism of skin injury in cutaneous lesions is not known, but antibody deposition is inconsistent and uncommon. Whether the myositis-specific antibodies are involved in disease pathogenesis is not yet known, although there is no direct evidence for this. An understanding of the reasons for production of these antibodies, however, should provide insight into the etiology and pathogenesis of PM and DM.

Characterization of an autoantigen associated with chronic ulcerative stomatitis: the CUSP autoantigen is a member of the p53 family.

A unique clinical syndrome has been described in which patients have chronic oral ulceration and autoantibodies to nuclei of stratified squamous epithelium. We have characterized the autoantibodies from patients sera and found that the major autoantigen is a 70 kDa epithelial nuclear protein. Sequencing of the cDNA for this protein, chronic ulcerative stomatitis protein, revealed it to be homologous to the p53 tumor suppressor and to the p73 putative tumor suppressor, and to be a splicing variant of the KET gene. The p53-like genes, p73 and the several KET splicing variants, are recently described genes of uncertain biologic and pathologic significance. This study provides the first clear association of a p53-like protein with a disease process.

A new approach to the classification of idiopathic inflammatory myopathy: myositis-specific autoantibodies define useful homogeneous patient groups.

The IIM are a heterogeneous group of systemic rheumatic diseases which share the common features of chronic muscle weakness and mononuclear cell infiltrates in muscle. A number of classification schemes have been proposed for them, but none takes into consideration the marked immunologic, clinical, and genetic heterogeneity of the various clinical groups. We compared the usefulness of myositis-specific autoantibodies (anti-aminoacyl-tRNA synthetases, anti-SRP, anti-Mi-2 and anti-MAS) to the standard clinical categories (polymyositis, dermatomyositis, overlap myositis, cancer-associated myositis, and inclusion body myositis) in predicting clinical signs and symptoms, HLA types, and prognosis in 212 adult IIM patients. Although patients with inclusion body myositis (n = 26) differed in having significantly more asymmetric and distal weakness, falling, and atrophy than other patients, there were few other significant differences among the other clinical groups. In contrast, autoantibody status defined distinct sets of patients and each patient had only 1 myositis-specific autoantibody. Patients with anti-amino-acyl-tRNA synthetase autoantibodies (n = 47), compared to those without these antibodies, had significantly more frequent arthritis, fever, interstitial lung disease, and "mechanic's hands"; HLA-DRw52; higher mean prednisone dose at survey, higher proportion of patients receiving cytotoxic drugs, and higher death rates. Those with anti-signal recognition particle antibodies (n = 7) had increased palpitations; myalgias; DR5, DRw52; severe, refractory disease; and higher death rates. Patients with anti-Mi-2 antibodies (n = 10) had increased "V-sign" and "shawl-sign" rashes, and cuticular overgrowth; DR7 and DRw53; and a good response to therapy. The 2 patients with anti-MAS antibodies were the only ones with alcoholic rhabdomyolysis preceding myositis; both had insulin-dependent diabetes mellitus, and both had HLA-B60, -C3, -DR4, and -DRw53. These findings suggest that myositis-specific autoantibody status is a more useful guide than clinical group in assessing patients with myositis, and that specific associations of immunogenetics, immune responses, and clinical manifestations occur in IIM. Thus the myositis-specific autoantibodies aid in interpreting the diverse symptoms and signs of myositis patients and in predicting their clinical course and prognosis. We propose, therefore, that an adjunct classification of the IIM, based on the myositis-specific autoantibody status, be incorporated into future studies of their epidemiology, etiology, and therapy.

Clinical manifestations in patients with antibody to PL-12 antigen (alanyl-tRNA synthetase).

PURPOSE: Anti-PL-12 antibody is directed at the enzyme alanyl-tRNA synthetase (ARS). Studies have clearly associated anti-Jo-1, also directed at an aminoacyl-tRNA synthetase (histidyl-tRNA synthetase), with a subgroup of myositis marked by a high frequency of interstitial lung disease (ILD) and arthritis. A similar syndrome has been reported in patients with antibodies to PL-12, but few patients have been studied. We describe the clinical manifestations in a new series of patients with antibody to PL-12. PATIENTS AND METHODS: Sera from patients with polymyositis and sera found to contain anticytoplasmic antibodies were screened for antibody to PL-12 by testing for inhibition of ARS enzymatic activity by serum, and by immunoprecipitation. RESULTS: Nine sera inhibited ARS. These nine plus two additional sera with anticytoplasmic antibodies immunoprecipitated an identical pattern of tRNAs and a polypeptide of 110 kd. Of the 10 patients that could be evaluated, eight had some evidence of myositis, including six that satisfied the criteria for myositis. Three of these six, all with dermatomyositis, had severe muscle involvement. Eight of the 10 patients had radiographic evidence of pulmonary fibrosis, and seven of the eight had clinical pulmonary impairment, including four with clinically severe ILD. Joint manifestations were found in five patients, and arthritis was the only clinical problem in one patient. CONCLUSION: We conclude that anti-PL-12, like anti-Jo-1 and anti-PL-7, was frequently associated with the "Jo-1 syndrome" of myositis with ILD. ILD was a major clinical problem in this group of patients.

Drug therapy of the idiopathic inflammatory myopathies: predictors of response to prednisone, azathioprine, and methotrexate and a comparison of their efficacy.

PURPOSE: To identify factors associated with responses to treatment with prednisone, methotrexate, or azathioprine in patients with idiopathic inflammatory myopathy, and to compare the efficacy of these drugs. PATIENTS AND METHODS: Data were collected on 113 adult patients meeting criteria for definite idiopathic inflammatory myopathy in this retrospective cohort study. Patients were categorized as responding completely, partially, or not at all to each therapeutic trial based upon clinical and laboratory criteria. RESULTS: Clinical group, presence of certain myositis-specific autoantibodies, and time from disease onset to diagnosis influenced rates of complete clinical response to these therapeutic agents. Patients with inclusion body myositis responded comparatively poorly to prednisone and the other drugs: 43% had no clinical response to prednisone and none responded completely to any medication. Patients with autoantibodies to aminoacyl-tRNA synthetases or to signal recognition particle proteins were likely to respond partially, but not completely, to prednisone. No patient with a long delay to diagnosis (greater than 18 months) responded completely, compared with 34% of those with a short delay (less than 3 months). A patient's response to the first course of prednisone predicted subsequent responses to prednisone and to azathioprine better than response to methotrexate. Men responded to methotrexate better than women. Among certain subgroups of patients, responses to methotrexate were better than to either azathioprine or retreatment with prednisone. CONCLUSION: Determining the clinical group, autoantibody status, and time from disease onset to diagnosis of patients with myositis provides useful information in predicting clinical responses to therapy, and these factors should be considered in designing future therapeutic trials. Methotrexate therapy may be superior to either azathioprine or further steroid treatment alone in certain patients who do not respond completely to an initial adequate course of prednisone.

Interstitial lung disease with autoantibodies against aminoacyl-tRNA synthetases in the absence of clinically apparent myositis.

Autoantibodies against aminoacyl-tRNA synthetases (antisynthetases) have been found to be highly specific for polymyositis and dermatomyositis and to correlate strongly with complicating interstitial lung disease (ILD). We describe the clinical presentations and course of 10 patients with ILD and anti-synthetase antibodies in whom underlying myositis was not clinically evident. Anti-PL-12 antibodies (antialanyl-tRNA synthetase) were most common (60%), followed by anti-Jo-1 (antihistidyl-tRNA synthetase) and anti-OJ (anti-isoleucyl-tRNA synthetase) (20% each). All 10 patients had anticytoplasmic antibodies by indirect immunofluorescence on HEp-2 cells. Five of 10 presented with features of connective tissue disease, whereas two presented with acute respiratory failure, two with insidious onset of diminished exercise tolerance, and one with persistent cough. All but one patient received corticosteroids, four were given oral cyclophosphamide, and two azathioprine. ILD resolved or stabilized in five patients (50%), and progressed in four (40%). The "antisynthetase syndrome" may occur in the absence of clinical myositis, and the ILD in these patients is usually responsive to therapy. Antisynthetase testing should be considered in patients with ILD who have a cytoplasmic pattern by antinuclear antibody (ANA) testing on HEp-2 cells, because early recognition and treatment of such patients affects their clinical course.

Immune manifestations of inflammatory muscle disease.

Evidence of autoimmune muscle injury and of systemic autoimmunity is seen in PM and DM. In typical PM, a cell-mediated attack on muscle fibers by CD8+ cytotoxic T cells predominates, directed at an unknown antigen. In DM, vascular injury is prominent, with loss of muscle capillaries and ischemic muscle damage, apparently mediated by local complement activation in small muscle vessels. Although humoral immunity seems more important in the pathogenesis of DM, serum autoantibodies are commonly found in both forms. About one third of patients have MSAs, whereas others have less specific antibodies such as anti-U1RNP, often associated with overlap syndromes involving myositis. MSAs are mutually exclusive and define characteristic clinical subgroups. Antibodies to five of the aminoacyl-tRNA synthetases are each associated with an "antisynthetase syndrome" marked by myositis, ILD, arthritis, and other features, but individual patients have only a single antisynthetase. Rare autoantibodies to certain translation factors may be associated with a similar syndrome. Anti-SRP is commonly associated with severe, acute, resistant myositis, whereas anti-Mi-2, the only MSA directed at a nuclear protein, is specifically associated with DM. Patients with anti-PM-Scl commonly have an overlap syndrome of PM/DM and SSc. Recent studies have recognized other antibodies in PM and DM, including antibody to endothelial cells, heat shock proteins, and, in a high proportion of patients, a 56-kd component of a ribonucleoprotein particle. The MSAs and their antigens are being characterized in detail. To date, data suggest similarity of predominant epitopes between different patients and a tendency toward conformational epitopes. It is not known if the recognized autoantibodies participate in tissue injury or pathogenetic processes, but production of the MSAs appears to be linked to etiologic factors and can be a clue to understanding the disease. Although these autoimmune responses are becoming better defined, the inciting events leading to generation of these responses and development of PM and DM remain unknown.

Autoantibodies in polymyositis.

A group of autoantibodies have been identified that are found almost exclusively in patients with polymyositis and dermatomyositis (myositis-specific antibodies). Most have been associated with characteristic clinical subgroups. Five of the myositis-specific antibodies are directed at aminoacyl-tRNA synthetases and have been associated with a similar clinical syndrome marked by myositis, interstitial lung disease, arthritis, and Raynaud's phenomenon (antisynthetase syndrome). Myositis-specific antibodies can help with patient diagnosis, subgroup classification, and possible prognosis. Their role in the pathogenesis of myositis remains to be defined, but their production is genetically influenced and appears to be linked to fundamental etiologic factors.

Autoantibodies to aminoacyl-transfer RNA synthetases for isoleucine and glycine. Two additional synthetases are antigenic in myositis.

Autoantibodies to three of the aminoacyl-transfer RNA (tRNA) synthetases have been reported (for histidine, threonine, and alanine). Most patients with these autoantibodies have polymyositis, and the majority also have interstitial lung disease. This study examined the question of whether autoantibodies to other aminoacyl-tRNA synthetases occur in the sera of myositis patients. We tested sera from patients with myositis with unidentified anticytoplasmic antibodies that immunoprecipitate tRNA for the ability to inhibit the aminoacyl-tRNA synthetases for the remaining 17 amino acids. Three sera showed strong inhibitory activity for a synthetase. OJ and NJ sera (and IgG) significantly inhibited isoleucyl-tRNA synthetase activity, each with 94% inhibition at the screening dilution, whereas other test sera and controls all inhibited less than 50%. OJ and NJ sera immunoprecipitated identical patterns of tRNA, and identical, complex patterns of high m.w. polypeptides that were consistent with the multienzyme synthetase complex of which isoleucyl-tRNA synthetase is a part. EJ serum (and IgG) significantly inhibited glycyl-tRNA synthetase, and immunoprecipitated a unique pattern of transfer RNA, and a strong predominant protein band of 77 kDa. These data strongly suggest that OJ and NJ have autoantibodies to isoleucyl-tRNA synthetase, and that EJ has antibodies to glycyl-tRNA synthetase. The findings of signs of muscle involvement in all three patients, and severe interstitial lung disease in OJ, strengthens the association of antisynthetases with these conditions.

Update on myositis-specific and myositis-associated autoantibodies.

Myositis-specific autoantibodies or myositis-associated autoantibodies can often be found in serum of patients with polymyositis and dermatomyositis. The presence of these autoantibodies can be significant in patient diagnosis and classification. Recent studies have provided new information about many of these specific autoantibodies. Among the more important developments were identification of a new antisynthetase, reacting with asparaginyl-tRNA synthetase; the detection of antibodies to the tRNA(his) in a over a third of anti-Jo-1 sera; and the description of distinctive features of the histopathology of patients with anti-Jo-1. New information about the cellular role of the antigens was discovered, including a role for Mi-2 antigen in chromosomally-mediated regulation of transcription as part of a nucleosome remodeling complex, and a potential role for PM-Scl antigen in ribosomal RNA processing as part of an exosome. The reason for the production of the autoantibodies, and the reason particular antigens are targeted, are key questions. Recent studies have suggested that antigen cleavage during apoptosis, particularly by granzyme B, may be an important factor. Whether the antibodies play a role in tissue injury remains unknown.

Measurement of antibody to Jo-1 by ELISA and comparison to enzyme inhibitory activity.

Antibody to the Jo-1 antigen (histidyl-tRNA synthetase) is found almost exclusively in myositis patients, usually those with adult PM, but has been found in only 30% of that group by immunodiffusion or other techniques thus far reported. We have reexamined the prevalence of antibody to Jo-1 in sera from 130 patients and 82 controls by using the sensitive ELISA technique. The ELISA used affinity-purified, enzymatically active bovine Jo-1 antigen. A wide range of antibody level by ELISA was found among 24 immunodiffusion positive sera. Six myositis and two control sera had apparent specific antibody detectable only by ELISA. Overall, however, the antibody continued to show high myositis specificity with predominance in adult PM (35.8% in that group). Because the antibody inhibits enzymatic activity of the synthetase antigen, we also studied the quantitative inhibitory activity of these sera to compare with the antibody activity as determined by ELISA. Twenty-four immunodiffusion-positive sera, 29 immunodiffusion-negative sera, and 15 normal sera were tested at 1/50 dilution in the reaction mixture. There was background inhibition by all normal sera tested that averaged 30.5%. All but one immunodiffusion negative myositis sera (a high binder by ELISA) inhibited less than 50% of the average with normal serum. Twenty-three of 24 immunodiffusion positive sera inhibited greater than 80% of this normal average; the other inhibited 66%. The serum dilution giving 50% inhibition was highly correlated (R = 0.83) with the ELISA activity. Thus, inhibition of histidyl-tRNA synthetase activity is a relatively accurate measure of Jo-1 antibody. This method should be applicable to measuring antibody to other aminoacyl-tRNA synthetases.

The association between Mi-2 antibodies and dermatomyositis.

Antibodies to Mi, an antigen in calf thymus extract, have been demonstrated by complement fixation inhibition in polymyositis (PM) and dermatomyositis (DM) sera but not in the sera of individuals without myositis. The original Mi reference serum defined 2 precipitating antibodies, using immunodiffusion (ID). Anti-Mi-1 was not active in complement fixation. We have now studied in further detail anti-Mi-2, which appears to be the antibody in Mi serum that fixes complement. Mi-2 antigen was purified by immuno-affinity chromatography. An enzyme-linked immunosorbent assay (ELISA) to measure Mi-2 antibody, using this antigen, was used to test the sera of 139 myositis patients: 52 had DM and 87 had PM. Control sera from 35 normal subjects and 93 patients with other connective tissue diseases were also tested. Only 13 sera were considered definitely positive for anti-Mi-2. All were from patients who had myositis, 11 of whom had DM. Only DM sera had anti-Mi-2 by ID, and all sera with anti-Mi-2 by ID were positive by ELISA. A number of other sera, including many from patients with other connective tissue diseases and 2 from normal subjects (all without precipitating antibodies) had lower elevations which were of uncertain significance. Detection of anti-Mi-2 by ID as well as by ELISA was significantly more frequent in DM than in PM. Anti-Mi-2 appears to be closely linked to DM, and is the first specific serologic marker for this form of myositis.