autoantibodies in pm and dm autoantibodies:>90% autoantibodies:>90% positive ana:60-80%...
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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 Absence does not exclude Assist in diagnosis and classification
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%
Anti-Synthetases: Indirect Immunofluorescence
Anti-Jo-1 Anti-OJ Anti-PL-12
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%
Anti-Mi-2: Indirect Immunofluorescence
Anti-Mi-2: Clinical Picture High specificity for myositis
low sensitivity Relative specificity for dermatomyositis Adults and children Rash often prominent
Anti-SRP: Indirect Immunofluorescence
Signal Recognition Particle Autoantibodies
Acute onset Severe weakness No skin involvement Biopsy may lack inflammation
Immune-mediated necrotizing myopathy
DIAGNOSIS and the Myositis Autoantibodies High specificity, Low sensitivity Define patient subgroups May help when extra-muscular features
predominate
Inclusion Body Myositis
Older age of onset Slow Progression
Longer duration to diagnosis Distal involvement: IBM>PM/DM
Forearm flexorsQuadriceps
Lesser degree of Creatine Kinase elevation
HISTOLOGIC FEATURES INCLUSION BODY MYOSITIS Light Microscopy
Rimmed vacuoles with basophilic granules
Eosinophilic inclusions Electron Microscopy
Inclusion bodies with microtubular filaments
Histopathology of IBMDalakas: Rheum Dis Clin NA 28:779,2002
Endomysial Inflammation
Sourrounding Non-necrotic fibers
Inclusion Body Myositis: Rimmed Vacuoles
IBM Pathology Dalakas Rheum Dis Clin NA 28:779,2002
Rimmed vacuoles; Basophilic Granules
EM:
Tubulofilaments
Extra-Muscular Manifestations
Systemic Pulmonary
Interstitial Lung Disease Respiratory Muscle Weakness Aspiration Infection Toxicity
Cardiac GI
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
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)
DRUG-INDUCED MYOPATHY
D-Penicillamine Zidovudine Lipid Lowering Agents Colchicine L-Tryptophan Drugs of Abuse Endocrine Chloroquine
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