Inflammatory myopathy: diagnosis and clinical course, specific clinical scenarios and new complementary tools

Abstract

Idiopathic inflammatory myopathies are a heterogeneous group of rare autoimmune diseases characterized by symmetric proximal muscle weakness and inflammatory infiltrates on muscle biopsy. A meticulously collected combination of clinical, serological, and pathological data is essential to correctly diagnose and classify myositis patients, often a considerable challenge for clinicians. This article provides a comprehensive overview of the most useful tools for the diagnosis and follow-up of patients with myositis. Capillaroscopy, serological biomarkers (particularly the autoantibody profile) and imaging techniques, such as muscle magnetic resonance and chest ultrasound, are of great aid in diagnosing, classifying and managing these patients. Relevant clinical scenarios, such as interstitial lung disease, associated cancer and pregnancy are also addressed in this review. Myositis registries, identification of new autoantibodies, and genetic studies will enhance our understanding of the pathogenesis of these conditions and help to define new diagnostic and therapeutic approaches.

Keywords:

• autoantibodies
• classification
• dermatomyositis
• diagnosis
• idiopathic inflammatory myopathies
• myositis
• polymyositis

Financial & competing interests disclosure

The authors were supported by a grant from the Spanish Ministry of Health and Consumer Affairs (PI12-01320). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Ms Celine Cavallo, an English language consultant reviewed the article.

Key issues

• Although several classifications and diagnostic criteria have been reported for idiopathic inflammatory myopathies, the diagnosis of these conditions mainly relies on accurate interpretation of combined clinical, serological and pathological data.

• The clinical course of patients with myositis varies considerably. Even so, patients can be categorized into three main groups in the first 2 years after disease onset – monocyclic, chronic polycyclic and chronic continuous – depending on the disease activity and frequency of relapse.

• Cancer-associated myositis occurs more often in patients with dermatomyositis. The relationship between myositis and cancer is paraneoplastic in nature (close temporal relationship), but the two conditions do not always follow the rule of presenting in parallel along time.

• The use of imaging techniques (PET/computed tomography) and new serological determinations (anti-TIF1-γ antibodies) will likely help in screening for occult cancer in dermatomyositis patients, although prospective studies addressing this topic are lacking.

• Complementary tools, such as capillaroscopy, whole-body muscle MRI and chest ultrasound study and serological markers, including new autoantibodies such as anti-MDA5, may be useful in the follow-up of myositis patients.

• Pulmonary function testing plays a central role in the control and follow-up of ILD in myositis patients.

• Many questions remain unsolved regarding anti-TIF1-γ autoantibodies, which seem to be relevant in the relationship between cancer and dermatomyositis. Progress in answering these questions is expected in the near future.

Notes