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Autoantibodies in PM and DM

Autoantibodies in PM and DM. Autoantibodies: >90% Positive ANA: 60-80% More in overlap Low in IBM Defined antibodies: 50% Myositis-specific antibodies: 35-40% Most common Ab (Jo-1): 20%. Myositis-Specific Antibodies. High disease specificity Appear prior to disease onset

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Autoantibodies in PM and DM

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  1. Autoantibodies in PM and DM • Autoantibodies: >90% • Positive ANA: 60-80% • More in overlap • Low in IBM • Defined antibodies: 50% • Myositis-specific antibodies: 35-40% • Most common Ab (Jo-1): 20%

  2. Myositis-Specific Antibodies • High disease specificity • Appear prior to disease onset • Absence does not exclude • Assist in diagnosis and classification

  3. Established Myositis-Specific Autoantibodies • Anti-synthetases 25% • Anti-Jo-1 20% • Non-Jo-1 4 - 8% • Anti-Mi-2 5 - 10% • Anti-SRP 5% • “signal recognition particle” • (Anti-PM-Scl) 5 - 10%

  4. Anti-Synthetases: Indirect Immunofluorescence Anti-Jo-1 Anti-OJ Anti-PL-12

  5. Anti-Synthetase Syndrome Myositis 95% Interstitial Lung Disease 70-90% Arthritis 50-90% Raynaud’s Phenomenon 60% Fevers 85% Recurrences 60% Mechanic’s Hands 70%

  6. Anti-Mi-2: Indirect Immunofluorescence

  7. Anti-Mi-2: Clinical Picture • High specificity for myositis • low sensitivity • Relative specificity for dermatomyositis • Adults and children • Rash often prominent

  8. Anti-SRP: Indirect Immunofluorescence

  9. Signal Recognition Particle Autoantibodies • Acute onset • Severe weakness • No skin involvement • Biopsy may lack inflammation • Immune-mediated necrotizing myopathy

  10. DIAGNOSIS and the Myositis Autoantibodies • High specificity, Low sensitivity • Define patient subgroups • May help when extra-muscular features predominate

  11. Inclusion Body Myositis • Older age of onset • Slow Progression • Longer duration to diagnosis • Distal involvement: IBM>PM/DM • Forearm flexors • Quadriceps • Lesser degree of CreatineKinase elevation

  12. HISTOLOGIC FEATURES INCLUSION BODY MYOSITIS • Light Microscopy • Rimmed vacuoles with basophilic granules • Eosinophilic inclusions • Electron Microscopy • Inclusion bodies with microtubular filaments

  13. Histopathology of IBMDalakas: Rheum Dis Clin NA 28:779,2002 Endomysial Inflammation Sourrounding Non-necrotic fibers

  14. Inclusion Body Myositis: Rimmed Vacuoles

  15. IBM PathologyDalakas Rheum Dis Clin NA 28:779,2002 Rimmed vacuoles; Basophilic Granules EM: Tubulofilaments

  16. Extra-Muscular Manifestations • Systemic • Pulmonary • Interstitial Lung Disease • Respiratory Muscle Weakness • Aspiration • Infection • Toxicity • Cardiac • GI

  17. Malignancy and Myositis • 32% DM, 15% PM • Risk greatest in 1st year • Increased risk in those age >45 • May have paraneoplastic course • Ovarian cancer overrepresented • Colon, lung, pancreatic, breast, lymphoma • Risk is higher with anti-p155/140 • lower with other myositis antibodies

  18. Differential Diagnosis of Idiopathic Inflammatory Myopathy • Other myopathies (dystrophy, metabolic) • Neuropathies (ALS, Myasthenia gravis) • Drug-induced myopathies • Infectious myopathies • Endocrine myopathies (hypothyroidism, Cushing’s syndrome)

  19. DRUG-INDUCED MYOPATHY • D-Penicillamine • Zidovudine • Lipid Lowering Agents • Colchicine • L-Tryptophan • Drugs of Abuse • Endocrine • Chloroquine

  20. Suggested Reading • Primer on the rheumatic diseases • For greater depth: • Miller FW: Inflammatory Myopathies: Polymyositis, Dermatomyositis, and Related Conditions (Chapter 75). In: Koopman et al, Arthritis and Allied Conditions

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