Measures of adult and juvenile dermatomyositis, polymyositis, and inclusion body myositis: Physician and Patient/Parent Global Activity, Manual Muscle Testing (MMT), Health Assessment Questionnaire (HAQ)/Childhood Health Assessment Questionnaire (C‐HAQ), Childhood Myositis Assessment Scale (CMAS), Myositis Disease Activity Assessment Tool (MDAAT), Disease Activity Score (DAS), Short Form 36 (SF‐36), Child Health Questionnaire (CHQ), Physician Global Damage, Myositis Damage Index (MDI), Quantitative Muscle

Abstract

The idiopathic inflammatory myopathies, including adult and juvenile dermatomyositis (DM), polymyositis (PM), and inclusion body myositis (IBM), are rare systemic autoimmune diseases that are characterized by chronic proximal muscle inflammation and weakness. In previous decades, there were few commonly used outcome measures in myositis, and those outcome measures were not validated. Thus, in the past the assessment of outcomes in therapeutic trials was focused on non-standardized measurement of muscle strength and function only. Over the last decade, however, two international collaborative groups, the International Myositis Assessment and Clinical Studies Group (IMACS) and the Paediatric Rheumatology International Trials Organisation (PRINTO), have defined consensus core set measures to assess myositis disease activity and damage in adults and children and have begun to validate and standardize these measures (1;2). IMACS and PRINTO have also developed preliminary definitions of improvement, which can be used as outcomes for therapeutic trials. These response criteria combine the core set activity measures to determine clinically meaningful improvement (3;4). Our section on myositis assessment focuses first on these core set measures of disease activity, quality of life (which is part of the PRINTO core set of activity, but a separate assessment domain for IMACS), and disease damage. To date, most of the validation data available for these core set measures are in patients with juvenile DM, with more limited validation in adult patients with DM or PM. Despite these efforts, there are still important gaps in validation of these core set measures, and no validation studies have yet been performed in patients with IBM, although they are now being used frequently in myositis therapeutic trials. We end the chapter with tools that have been used primarily in research studies and a few therapeutic trials, which have some supporting validation in certain subgroups of patients with myositis. These tools are primarily organ-specific measures, including strength and functional assessments and cutaneous assessment tools. Quantitative muscle testing and the IBM Functional Rating Scale are the most commonly used instruments to assess patients with IBM, and although they have little supporting validation in myositis, quantitative muscle testing has been well validated in other myopathies and has been used frequently as an endpoint in therapeutic trials for IBM. Although the methods for the assessment of myositis patients have been limited in their scope, great strides have been made in the last decade in the development of new partially validated tools (see Table 1) and international multidisciplinary consensus in using these measures that should enhance our understanding of the diverse effects of myositis on many organ systems and the development of new therapies. Table 1 Summary of Measures of Disease Activity in Myositis Physician and Patient/Parent Global Activity General Description Purpose An overall rating of the disease activity related to myositis, defined as potentially reversible pathology or physiology resulting from the underlying disease process (1).