Inflammatory myopathies Flashcards
4 subtypes of inflammatory myopathies
dermatomyositis
polymyositis
necrotizing autoimmune myositis
inclusion body myositis
General features of inflammatory myopathies
elevated CK, weakness or myalgia, and in patients with suggestive skin findings
abnormal liver function tests (esp. AST>ALT)
Findings of dermatomyositis?
symmetrical proximal muscle weakness dysphagia Grotton papules heliotrope rash photodistributed rash (shawl/V sign) myositis ILD Raynaud's arthritis mechanic's hand rash anti-RNA and anti-Jo1 Ab tissue bx: perivascular, perimysial, perifascicular inflammation, necrotic fibers in wedge like infarcts, perifascicular atrophy Higher risk for cancer, pan scan
Findings of polymyositis?
symmetrical proximal muscle weakness dysphagia ILD Raynaud's arthritis mechanic's hand rash anti-RNA and anti-Jo1 Ab tissue bx: CD 8+ cells invading healthy fibers, widespread expression of MHC class I Ag, no vacuoles
Findings of Necrotizing autoimmune myositis
symmetrical proximal muscle weakness
dysphagia
Raynaud’s
arthritis
mechanic’s hand rash
anti-RNA and anti-Jo1 Ab, anti-SRP, anti-HMGCR
tissue bx: scattered necrotic fibers with macrophages, no CD8+ cells or vacuoles, complement deposit on capillaries
Findings of Inclusion body myositis
slow onset asymmetrical weakness of any muscle group, facial weakness, atrophy, falls tissue bx: CD8+ cells invading healthy fibers, autophagic vacuoles, widespread expression of MHC class I Ag, ragged-red/blue fibers, congo-philic amyloid deposition
General work up for inflammatory myopathy
Hx: statin exposure, concomitant autoimmune diseases or inflammatory arthritis, distribution and involvement of muscle weakness, cutaneous manifestations for DM and antisynthetase syndrome, sxs malignancy
Labs: CK, AST, ALT, LDH, ANA, anti-Ro and anti-La Ab, RF, myositis-specific Ab (including HMG-CoA Ab)
Imaging: MRI bilateral limbs: distribution of muscle inflammation, aid target for bx
fat-suppressed MRI sequence: muscle inflammation,(muscle edema =active disease; muscle atrophy and fatty replacement=muscle damage w/o disease activity)
Dx: tissue bx of targeted area or blindly of vastus lateralis, histologic, immunohistochemical, and electron microscopic features
Treatment for dermatomyositis, polymyositis, and necrotizing autoimmune myositis
prednisone 1mg/kg 4-6w then taper >azothioprine, MTX, mycophenolate> IVIG
Treatment for inclusion body myositis
PT, research trials
