Diagnosis and classification of idiopathic inflammatory myopathies

Abstract

The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of diseases, collectively named myositis, sharing symptoms of muscle weakness and muscle fatigue and inflammation in muscle tissue. Other organs are frequently involved supporting that these are systemic inflammatory diseases. The IIMs can be sub-grouped into dermatomyositis, polymyositis and inclusion body myositis. The myositis-specific autoantibodies (MSAs) identify other and often more distinct clinical phenotypes, such as the anti-synthetase syndrome with antisynthetase autoantibodies and frequent interstitial lung disease (ILD) and anti-SRP and anti-HMGCR autoantibodies that identify necrotizing myopathy. The MSAs are important both to support myositis diagnosis and to identify subgroups with different patterns of extramuscular organ involvement such as ILD. Another cornerstone in the diagnostic procedure is muscle biopsy to identify inflammation and to exclude non-inflammatory myopathies. Treatment effect and prognosis varies by subgroup. To develop new and better therapies, validated classification criteria that identify distinct subgroups of myositis are critical.. The lack of such criteria was the main rationale for the development of new classification criteria for inflammatory myopathies, which are summarized in this review, along with an historical background on previous diagnostic and classification criteria. As these are rare diseases with a prevalence of 10 in 100 000 individuals an international collaboration was essential, as was the interdisciplinary effort including adult and paediatric experts in rheumatology, neurology, dermatology and epidemiology. The new criteria have been developed based on data from more than 1 500 patients from 47 centers world-wide and are based on clinically easily available variables.

Lesson of the month 2: Dry skin, yellow nails and breathlessness

“…1 The latter is a pathonomonic feature of hyperkeratotic, fissured skin on the palmar and lateral aspects of the fingers, typically the thumb, index and middle fingers. Occasionally, these changes result in irregular, dirty-appearing horizontal lines that resemble those of a manual labourer.…”

Idiopathic inflammatory myopathies – a guide to subtypes, diagnostic approach and treatment

“…Separate criteria for these conditions and antisynthetase syndrome are now available. 29 Depending on the number of criteria fulfilled, a label of possible, probable or definite DM/PM could be assigned. In an effort to include advances in IIM presentation and identification of MSAs, the International Myositis Assessment and Clinical Studies (IMACS) Group are developing the International Myositis Classification Criteria Project (IMCCP) classification criteria.…”

“…In an effort to include advances in IIM presentation and identification of MSAs, the International Myositis Assessment and Clinical Studies (IMACS) Group are developing the International Myositis Classification Criteria Project (IMCCP) classification criteria. 29 The IMCCP classification criteria will take the form of an individual's probability of having an IIM. Classification as an IIM using the IMCCP criteria requires a probability higher than 50% and the cut off for inclusion into a clinical trial is a probability higher than 90%.…”

The Clinical and Pathological Spectrum of Idiopathic Inflammatory Myopathies : Implications for pathogenesis, classification and diagnosis

“…The prime purpose of classification criteria is to allow comparison between different studies of the same disease, and is not meant for clinical diagnosis [241]. Despite the inherent risks, they have, however, often served as guides for clinicians.…”

“…New classification criteria by the international myositis assessment and study group (IMACS) are currently under review and will be published soon [241].…”