Table 2

Overview of myositis specific antibodies and contribution to clinical decisions.

MSA	Criticality/comment	Relevance/criticality
HMGCoA reductase	The presence of anti-HMGCR antibodies predicts poor response to corticosteroid and immunosuppressant therapy. This anticipation is relevant for the clinician.	Relevant, not critical; however, false negative might lead to omission of biopsy
TIF1y	Strong association with malignancy in elderly patients. Extensive screening for malignancy is necessary prior to treatment of IIM.	Critical, false negative result might lead to delayed diagnosis of cancer
SRP	Associated with severe treatment resistant myopathy, leading to long term immunosuppressive therapy The presence of SRP antibodies predicts poor response to corticosteroid and immunosuppressant therapy. This anticipation is relevant for the clinician.	Relevant, not critical; however, false negative might lead to omission of biopsy
MDA5	Positive result should trigger screening for ILD and if confirmed more aggressive treatment and clinical vigilance	Critical, False negative result may lead to less intensive (respiratory) monitoring with a delay
PM/Scl	In general, associated with a milder disease course	Not critical, low relevance
Ku	Often associated with SLE and/or SSc. Requires monitoring and treatment to coexisting SLE and/or SSc, especially when other antibodies are present (eg, anti-dsDNA).12	Relevant, not critical
SAE	Severe cutaneous disease that classically precede DM with severe dysphagia and systemic symptoms.	Relevant, not critical
NXP2	Juvenile DM, diffused calcinosis. Cancer associated DM triggers consideration for screening for concurrent malignancy prior to treatment initiation.	Critical, similar to TIF1y, however, less pronounced
Mi-2	In general, associated with a milder disease course. If present without other MSA, reassures relatively mild disease phenotype.	Relevant, not critical; false positive can lead to a wrong perception of milder disease (no monitoring for ILD)
Jo-1, EJ, OJ, PL-7, PL-12	Positive result triggers the clinician to screen for ILD and to prospectively follow-up pulmonary function; often requires long-term immunosuppressive treatment Predicts better therapeutic response to rituximab13 Influences patient management when pulmonologists identify these antibodies in patients with unexplained ILD Consider immunosuppressant strategies Follow-up for appearance of extra-pulmonary manifestations of the antisynthetase syndrome14	Relevant, not critical; False negative results might have a negative effect on optimal therapy choice in severe myositis (more arguments for rituximab) and patients with unexplained ILD (as single manifestation) might experience delay in diagnosis.

DM, dermatomyositis; IIM, idiopathic inflammatory myopathies; ILD, interstitial lung disease; MSA, myositis specific antibodies; SLE, systemic lupus erythematosus; SSc, systemic sclerosis.