Diagnosis of systemic autoimmune myopathies-Brazilian Society of Rheumatology guidelines

The Brazilian Society of Rheumatology has released its latest guidelines on investigation and diagnosis of systemic autoimmune myopathies.The guidelines have been published in the journal Advances in Rheumatology

What are the classification criteria for SAM?

SAM classification criteria may help with diagnoses, provided other myopathies have been ruled out. Specifically, the EULAR / ACR criteria deserve special mention, mainly when associated with muscle biopsy (quality of evidence B; level of agreement > 90%).

When should muscle biopsy be indicated in patients with SAM?

Muscle biopsy in patients with SAM may aid in the diagnosis of their subtypes and differentiate this disease from noninflammatory myopathies. MHC labeling mainly contributes to differentiating SAM from muscular dystrophies (quality of evidence B, level of agreement > 90%).

When should magnetic resonance imaging of muscles be indicated in patients with SAM?

Magnetic resonance images can be used as a guide to
biopsy, to identify oligosymptomatic myositis and possible kinds of myopathies, and to monitor disease progression and response to treatment (quality of evidence B, level of agreement > 90%).

When should electroneuromyography be indicated in patients with SAM?

Electroneuromyography in the diagnostic investigation can identify patients with myopathies, but it plays no role in the follow-up (quality of evidence B; level of agreement > 90%).

What are the myositis-specific or myositis-related antibodies that can assist in the diagnosis and/or follow-up of SAM patients in daily practice?

Autoantibodies can be found in patients diagnosed with SAM. They are not essential to the treatment but are useful in doubtful cases to accrue prognostic information and associated manifestations (quality of evidence B; level of agreement > 90%).

In the initial and late phases, which types of cancers should be searched for SAM? How often should the screening be done?

There is no concise information about the screening of neoplasms, and no consensus, regarding how and when this screening should be conducted. However, in our opinion, adults with this diagnosis, highlighting DM, should be screened, requesting specific tests mainly according to gender, age, ethnicity, and familiar history (quality of evidence B; level of agreement > 90%).

Which comorbidities should be (re) evaluated regularly in patients with SAM?

The management of patients with myopathies should consider care aimed at limiting the effects of muscle weakness, on joints, bones and other systems. In addition, comorbidities should be screened for and treated when necessary, optimizing the functional capacity and thereby improving quality of life of patients (quality of evidence B; level of agreement > 90%).

What are the main differential diagnoses of SAM?

Several conditions may mimic the clinical manifestations of SAM. Moreover, the absence of specific autoantibodies and systemic features related to autoimmunity and refractoriness to immunosuppressive drugs should also raise the suspicion of alternative diagnoses (quality of evidence B; level of agreement > 90%).

Which clinical / laboratory findings result in poor response to drug treatment in SAM?

• Cytokines and specific or related myositis antibodies aiming to discriminate the disease activity and to predict the prognosis of the treatment. However, it is important to note that the available evidence on the use of laboratory findings for this purpose shows variable results in terms of performance, lacking a standardized approach (quality of evidence B; level of agreement > 90%).


• The available evidence on the use of laboratory tests or other standardized tools to evaluate disease activity and/or to predict the response to treatment shows variable results in terms of performance, lacking a standardized approach. At this point, we recommend the use of laboratory markers, such as CPK, and tools, such as physician and patient global evaluation of the disease activity as guides to disease activity, and treatment response (quality of evidence B; level of agreement > 90%).

Which organs and/or systems should be routinely reevaluated in patients with SAM?