Dermatomyositis

At the first assessment, document the distribution and severity of weakness and actively elicit dysphagia. A characteristic dermatomyositis eruption with little or no objective weakness should trigger evaluation for clinically amyopathic dermatomyositis rather than dismissal as skin-limited disease, because autoantibody-defined dermatomyositis phenotypes may have mild weakness or clinically amyopathic presentations. Wolters KluwerWolters KluwerDiagnostic classification of dermatomyositis with and... : Singapore Medical Journal

Evaluate pulmonary involvement at diagnosis even without respiratory symptoms. Interstitial lung disease may be asymptomatic and is a major source of morbidity and mortality in dermatomyositis; in juvenile dermatomyositis it is reported in approximately 8% of patients. BMJBMJConsensus-based recommendations for the management of juvenile dermatomyositis | Annals of the Rheumatic Diseases New dyspnea, cough, hypoxemia, restrictive physiology, or impaired diffusion capacity should accelerate high-resolution chest CT and pulmonary collaboration rather than be attributed solely to respiratory muscle weakness. BMJBMJConsensus-based recommendations for the management of juvenile dermatomyositis | Annals of the Rheumatic Diseases

In adults, establish the interval between dermatomyositis onset and any known or suspected cancer before selecting screening intensity. Cancer risk is concentrated from 3 years before through 3 years after IIM onset; the diagnostic evaluation should therefore seek occult malignancy as well as recurrence or progression of known cancer. NatureNatureInternational Guideline for Idiopathic Inflammatory Myopathy-Associated Cancer Screening: an International Myositis Assessment and Clinical Studies Group (IMACS) initiative | Nature Reviews Rheumatology Anti-TIF1γ positivity is associated with a paraneoplastic dermatomyositis phenotype and has pooled specificity of 89% for paraneoplastic dermatomyositis in the cited report. BMJBMJNew-onset dermatomyositis in a patient on nivolumab for metastatic melanoma | BMJ Case Reports

Start with a focused neuromuscular examination that distinguishes symmetric proximal weakness from distal-predominant, asymmetric, fatigable, or neurogenic patterns. The diagnostic assessment of inflammatory myopathy requires detailed characterization of weakness supported by laboratory, imaging, and histopathologic findings; CK and inflammatory markers are nonspecific and should not be treated as diagnostic in isolation. Wolters KluwerWolters KluwerDiagnostic classification of dermatomyositis with... : Singapore Medical Journal

Order a myositis-specific and myositis-associated antibody panel concurrently with the initial biopsy decision. Myositis-specific antibodies are not universal—reported in about 60% of dermatomyositis cases—but provide clinically useful information about likely ILD, malignancy, and treatment-response phenotypes. BMJ+1BMJMuscle biopsyBMJpractneurol-2019-002465 1..11 - Practical Neurology Interpret a negative result as nonconfirmatory, not exclusionary.

Use muscle MRI to identify active muscle edema and to direct biopsy in patients with patchy disease, inconclusive prior pathology, or discordance between symptoms and routine testing. STIR hyperintensity can identify an active target; a false-negative biopsy can occur because inflammatory pathology is patchy. BMJ+1BMJMuscle biopsyBMJpractneurol-2019-002465 1..11 - Practical Neurology If electromyography does not show a myopathic recruitment pattern or spontaneous activity despite apparent clinical weakness, reconsider alternative diagnoses rather than accepting elevated CK as proof of inflammatory myopathy. Wolters KluwerWolters KluwerDiagnostic classification of dermatomyositis with... : Singapore Medical Journal

Choose pathology according to the dominant diagnostic question. In a patient with classic dermatomyositis rash and mild weakness, antibody testing may reasonably precede muscle biopsy. BMJ+1BMJMuscle biopsyBMJpractneurol-2019-002465 1..11 - Practical Neurology In patients with atypical weakness, absent hallmark rash, negative or equivocal serology, or a plausible muscular dystrophy, metabolic myopathy, neurogenic disorder, or inclusion body myositis, obtain tissue or alternative targeted testing rather than assigning dermatomyositis empirically. BMJ+2BMJMuscle biopsy - Practical NeurologyBMJpractneurol-2019-002465 1..11 - Practical NeurologyWolters KluwerDiagnostic classification of dermatomyositis with... : Singapore Medical Journal

Obtain pulmonary function tests including diffusing capacity for carbon monoxide at diagnosis in juvenile dermatomyositis; this consensus recommendation reflects that ILD may be clinically silent. BMJBMJConsensus-based recommendations for the management of juvenile dermatomyositis | Annals of the Rheumatic Diseases In adults, use the same diagnostic principle: pulmonary symptoms alone are insufficient to exclude lung disease in a myositis phenotype, particularly when antibody testing suggests an ILD-associated phenotype. BMJ+1BMJMuscle biopsyBMJpractneurol-2019-002465 1..11 - Practical Neurology

An abnormal restrictive pattern should trigger further evaluation, preferably with pulmonary involvement. BMJBMJConsensus-based recommendations for the management of juvenile dermatomyositis | Annals of the Rheumatic Diseases Interpret low volumes cautiously in severe generalized weakness because respiratory muscle weakness can impair spirometry and test performance; evaluate diffusion capacity and imaging rather than inferring parenchymal ILD from restriction alone. BMJBMJConsensus-based recommendations for the management of juvenile dermatomyositis | Annals of the Rheumatic Diseases

Use high-resolution CT when pulmonary physiology is abnormal or clinical suspicion persists. HRCT is sensitive and noninvasive for ILD detection, but repeated scanning creates radiation exposure; repeat imaging when it will change management rather than as automatic surveillance. BMJBMJConsensus-based recommendations for the management of juvenile dermatomyositis | Annals of the Rheumatic Diseases

Perform cancer-risk stratification at the time adult-onset dermatomyositis is diagnosed. IMACS identifies high-risk factors across IIM subtype, autoantibody, and clinical-feature domains, and classifies patients with two or more high-risk factors as high risk for IIM-related cancer. NatureNatureInternational Guideline for Idiopathic Inflammatory Myopathy-Associated Cancer Screening: an International Myositis Assessment and Clinical Studies Group (IMACS) initiative | Nature Reviews Rheumatology Adult-onset dermatomyositis itself and age greater than 40 years at diagnosis were the most prevalent high-risk features in a multinational audit. BMJBMJMulticentre international audit of IMACS malignancy screening guidelines in idiopathic inflammatory myopathies: insights from the myositis audit and research collaborative group | RMD Open

Use anti-TIF1γ results to intensify clinical concern rather than as a stand-alone cancer diagnosis. For anti-TIF1γ-positive dermatomyositis with onset after age 40 years and at least one additional high-risk clinical feature, IMACS conditionally recommends considering FDG PET-CT as a single screening investigation. NatureNatureInternational Guideline for Idiopathic Inflammatory Myopathy-Associated Cancer Screening: an International Myositis Assessment and Clinical Studies Group (IMACS) initiative | Nature Reviews Rheumatology PET-CT is also a conditional option for any high-risk adult-onset IIM patient when cancer has not been detected on investigations at diagnosis. NatureNatureInternational Guideline for Idiopathic Inflammatory Myopathy-Associated Cancer Screening: an International Myositis Assessment and Clinical Studies Group (IMACS) initiative | Nature Reviews Rheumatology

Do not reduce screening intensity solely because the patient has ILD, Raynaud phenomenon, inflammatory arthritis, a non-Jo-1 antisynthetase antibody, or a myositis-associated antibody; IMACS lists these as intermediate or low-risk factors, and they contribute to the overall risk framework rather than replacing it. NatureNatureInternational Guideline for Idiopathic Inflammatory Myopathy-Associated Cancer Screening: an International Myositis Assessment and Clinical Studies Group (IMACS) initiative | Nature Reviews Rheumatology Conversely, persistent disease activity despite immunosuppression was a commonly observed high-risk feature in the audit and should prompt reassessment of occult malignancy in the appropriate clinical setting. BMJBMJMulticentre international audit of IMACS malignancy screening guidelines in idiopathic inflammatory myopathies: insights from the myositis audit and research collaborative group | RMD Open

Separate muscle, skin, lung, and malignancy surveillance at follow-up. CK can remain normal in clinically meaningful dermatomyositis, while skin-predominant disease may require serial structured skin assessment; in juvenile dermatomyositis, consensus supports use of a cutaneous assessment tool, although no single instrument has demonstrated superiority. BMJ+2BMJConsensus-based recommendations for the management ...BMJFRI0524 Juvenile Dermatomyositis (DM) with Normal Creatine Kinase | Annals of the Rheumatic DiseasesScienceDirectFRI0524 Juvenile Dermatomyositis (DM) with Normal Creatine Kinase - ScienceDirect

For a patient whose biopsy is nondiagnostic but whose phenotype evolves toward dermatomyositis, reassess the target rather than treating a negative sample as definitive. Repeat STIR MRI to identify active edematous muscle before another biopsy because patchiness is a recognized cause of false-negative pathology. BMJ+1BMJMuscle biopsyBMJpractneurol-2019-002465 1..11 - Practical Neurology

Do not infer that a newly emerging rash or weakness is ordinary dermatomyositis relapse without revisiting medication and cancer context. Nivolumab-associated dermatomyositis has been reported, and anti-TIF1γ-positive disease may reflect paraneoplastic autoimmunity; both settings change the multidisciplinary diagnostic and treatment discussion. BMJBMJNew-onset dermatomyositis in a patient on nivolumab for metastatic melanoma | BMJ Case Reports