Abstract
Inflammatory myositis presents variably, not necessarily with muscle symptoms. Diagnosis can be challenging, potentially helped by biochemical and immunological tests, neurophysiology and imaging. A normal creatine kinase (CK) may dissuade clinicians from considering myositis; however, there is growing evidence for amyopathic, hypomyopathic and normal CK subsets.
CHARTS Software was used to identify patients seen by rheumatology or neurologyat University Hospital Southampton between 01/06/2023 and 01/06/2024 usingsearch terms “myositis”, “dermatomyositis”, “polymyositis”, “synthetase” and “anti-synthetase”.Data were collected for patients managed for an inflammatory myositis.
269 patients were identified; 72 were being managed for inflammatory myositis, 25 had a normal CK (20-291 U/L). Data collected for those 25 reflected diagnoses: 8 anti-synthetase syndrome, 7 dermatomyositis, 4 amyopathic dermatomyositis, 4 non-specific/polymyositis, 1 paraneoplastic myositis and 1 scleroderma/myositis overlap. Common presenting symptoms were muscle, cutaneous, respiratory, and joint, affecting 12 (48%), 18 (72%), 11 (44%) and 12 (48%) patients respectively. Less frequent symptoms included gastrointestinal symptoms, dysaesthesia, headaches, fatigue, fever, sicca symptoms, sweats, weight loss and Raynaud’s. Table 1 reflects patients’ investigations. The data reflect that 52% patients had no muscle symptoms at diagnosis; these patients did not have muscle imaging or electromyography. 44% had interstitial lung disease (ILD). All patients positive for MDA5 had cutaneous features. All patients positive for Anti-Ro52 had ILD. A patient who was not screened for malignancy was incidentally found to have lung cancer during methotrexate work up.
Increasing evidence supports that a raised CK and muscle symptoms are not required to diagnose inflammatory myositis, and that active myositis can be present despite the absence of these features. Antibody testing and muscle MRI are useful but not definitive diagnostic tests. Extra-muscular symptoms may precede myositis and lack of muscle symptoms does not reduce risk of potentially fatal disease associations, such as ILD and malignancy. Further study may provide guidance on how to reliably exclude inflammatory myositis to optimise management of resources and referrals. Greater awareness is required regarding the phenotypic features of different types of inflammatory myositis so that patients with subsets featuring a normal CK receive a timely diagnosis, safe screening and monitoring, and optimal care.
E.C. Rose: None.
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