In the present study, anti-Jo-1 positivity was observed in 8.5% of patients with definite DM, and it was associated with “mechanic’s hands,” as well as joint and lung involvement.
In contrast, anti-Jo-1-positive patients exhibited a decreased frequency of skin manifestations such as facial erythema, “shawl” sign, and “V-neck” sign compared to anti-Jo-1-negative patients.
The frequency of anti-Jo-1 positivity ranges from 5 to 20% in the literature [6, 7, 9, 10, 13], and such wide variation occurs because of the different ethnic groups evaluated, which included Indians , Europeans , Brazilians , and cohorts comprising patients from multiple ethnicities . In the present study, the prevalence of anti-Jo-1 positivity was 8.5% in Brazilian patients, which is within the range found in the literature. However, unlike other published research [9, 10, 12,13,14, 16], the presence of anti-Jo-1 autoantibodies was evaluated in a sample comprising only patients with DM in the present study. Moreover, only patients exclusively with definite DM were included, and patients with possible or probable DM, according to both the EULAR/ACR 2017  and the Bohan and Peter criteria [1, 2], were excluded. Patients with clinically amyopathic DM, myositis associated with neoplasia or other systemic autoimmune disorders, and patients with other myositis-specific (e.g., anti-OJ, -EJ, -PL-7, and -PL-12) or myositis-associated (e.g., anti-Ku and anti-PM/Scl) autoantibodies were also excluded. Although this was a retrospective study, patient data were collected from records containing previously parameterized and standardized information, including that of interest to the present study.
Although the manifestations of DM are primarily cutaneous and muscular, we observed a significant prevalence of joint involvement in our cohort. We also identified a strong association between anti-Jo-1 positivity and the occurrence of joint involvement in our sample. This association has also been found in other studies. For instance, in a large European cohort  comprising 1637 patients with probable or definite DM, or polymyositis (PM) according to the Bohan and Peter criteria [1, 2], arthritis was strongly associated with anti-Jo-1 positivity. In addition, in a study by Ohashi et al. , japanese patients with systemic autoimmune myopathies and anti-Jo-1 positivity frequently presented with joint symptoms. Such an association between arthralgia or arthritis and anti-Jo-1 positivity has also been observed among patients with multiple types of idiopathic inflammatory myopathies [9, 12, 14]. Thus, a marked influence of anti-Jo-1 autoantibodies on the phenotype of patients with DM and joint involvement can be inferred.
The cutaneous lesions known as “mechanic’s hands,” classically associated with antisynthetase syndrome, are characterized by hyperkeratosis, scaling, and fissuring affecting the phalanges of the hands . The correlation between anti-Jo-1 autoantibodies and “mechanic’s hands” has been described for Indian and Japanese patients with systemic autoimmune myopathies [10, 12]. In a meta-analysis of 27 studies that included 3487 patients with idiopathic inflammatory myopathies, Lega et al.  observed that the frequency of “mechanic’s hands” increased by about 50% among patients with anti-Jo-1 autoantibodies compared to patients positive for other anti-aminoacyl-tRNA synthetase autoantibodies. Anti-Jo-1 positivity was also associated with an increased frequency of “mechanic’s hands” among DM patients in the present study. This finding is also corroborated by Srivastava et al. , who found that patients with antisynthetase antibodies as a group and those with anti-Jo-1 antibodies alone had significantly more “mechanics’ hands,” while this association was not noted with other non-Jo-1 antisynthetase autoantibodies.
As for the other DM skin lesions, we observed a reduced prevalence of facial erythema, “shawl” sign, and “V-neck” sign, and no digital ulcers or calcinosis cutis among our anti-Jo-1-positive patients. Thus, this autoantibody might act as a protective factor against these cutaneous manifestations; however, further research is needed to investigate this hypothesis.
Interstitial lung disease is associated with increased morbidity and mortality in patients with idiopathic inflammatory myopathies [18, 19]. We observed a strong association between anti-Jo-1 autoantibodies and lung involvement, including clinical (dyspnea) and radiographic abnormalities on high-resolution CT imaging suggestive of interstitial lung disease. Anti-Jo-1 positivity is indeed associated with interstitial lung disease as defined by imaging findings alone  or together with abnormal pulmonary function testing [10, 12,13,14,15,16,17]. In our cohort, not all patients underwent pulmonary function testing, and therefore we did not include those data in the present study. However, previous research [6, 10, 12,13,14,15,16,17] has examined heterogeneous samples of patients with systemic autoimmune myopathies, and also has included cases of probable DM or PM, defined according to the Bohan and Peter criteria [1, 2] as well as overlap syndromes [10, 16]. Furthermore, no additional analysis to exclude potential cases of antisynthetase syndrome [10, 12, 13, 15, 17], which might also affect the lungs [20,21,22], has been performed.
We also found that anti-Jo-1 positivity was associated with lung involvement in patients with definite DM. We excluded patients who were positive for other anti-aminoacyl-tRNA synthetase autoantibodies, anti-Ku, and anti-PM/Scl to avoid biasing the interpretation of our data, as they are also associated with lung involvement [20, 23, 24].
As for other autoantibodies, anti-Ro-52 is a myositis-associated antibody and is commonly related to anti-Jo-1 positivity [6, 9, 16, 25]. The co-occurrence of anti-Ro-52 and anti-Jo-1 positivity was reported by Marie et al.  to be prevalent in patients with systemic autoimmune myopathies, suggesting that the simultaneous presence of these autoantibodies is associated with an increased risk of severe interstitial lung disease, more severe myositis, joint involvement, and neoplasia in patients older than 50 years. A potential explanation for the fact that anti-Ro-52 positivity was not associated with the occurrence of anti-Jo-1 autoantibodies in the present study is the small size of our sample.
Anti-Mi-2 positivity is known to be associated with the classical DM skin findings [25,26,27], to be a protective factor for lung involvement [25, 26], and a marker of high rates of remission  and response to glucocorticoid therapy [25, 26]. No anti-Jo-1-positive patients in our sample were found to be positive for anti-Mi-2 autoantibodies, which reaffirms the reports in the literature suggesting myositis-specific antibodies are mutually exclusive .
Concerning treatment, patients with anti-Jo-1 autoantibodies were found to be more frequently on glucocorticoids and immunosuppressive drugs when compared to those negative for this autoantibody. Consequently, no anti-Jo-1-positive patients had achieved disease remission at the time of their last medical evaluation, whereas one third of those negative for this autoantibody had gone into clinical remission. Patients in remission are referred to follow-up at primary or secondary care facilities as per our local protocol, which is why approximately half of the anti-Jo-1-negative DM patients had not been receiving follow-up treatment at the time.
No cases of neoplasia were observed during follow-up, but 10% of patients died, with no difference between the groups. Relapse rates were also similar between groups.
As a major limitation of our study, we had a small number of patients with anti-Jo-1 autoantibodies, and so our results should be interpreted with caution. Moreover, since this is a retrospective study, we did not have complete data available, such as serum levels of creatine phosphokinase and aldolase at disease onset or diagnosis or serum levels of the other muscle enzymes (aspartate aminotransferase, alanine aminotransferase, lactic dehydrogenase).