Katie DePlatchett, M.D.AM Report

May 26, 2010

Inflammatory Myopathies

Infammatory MyopathiesPolymyositisDermatomyositisInclusion body myositisOverlap myositis – related to

connective tissue disorderCancer-associated myositis

myositis with clinical paraneoplastic features and without an overlap autoantibody

PolymyositisSymmetric proximal muscle weaknessElevated serum muscle enzymes*

CK, CK-MB, AST, ALT, LD, AldolaseMyopathic changes on EMGMuscle biopsy

cellular infiltrate is predominantly within the fascicle with inflammatory cells invading individual muscle fibers

cell–mediated, increased numbers of cytotoxic CD8+ T cells, which appear to recognize an antigen on the muscle fiber surface

Polymyositis - histopathology

DermatomyositisSymmetric proximal muscle

weaknessElevated serum muscle enzymesMyopathic changes on EMGMuscle biopsy

humorally–mediated disorder (CD4 cells), cellular infiltrate, located principally in perifascicular regions, focused around blood vessels 

Rash

Dermatomyositis - histology

Dermatomyositis – skin findingsGottron’s signHeliotrope rashShaw sign & V signMechanic’s handsPsoriasiform changes in scalp

What about auto-antibodies???ANA present in up to 80% of myositis-specific autoantibodies:

anti-Jo-1, highly specific, associated w/ ILD

anti-SRP antibodiesantibodies to Mi-2, (a nuclear helicase)

Not diagnostic but affects prognosis

Inclusion body myositisinsidious onset more prominent distal muscle

weakness & atrophy (wrists, fingers, anterior tibial)

Asymmetric muscle involvementOn average, serum muscle enzyme

levels are lower in IBM than in PMpresence of typical inclusion bodies

on muscle biopsy

Overlap MyositisMyopathy associated with the other

connective tissue diseases scleroderma, systemic lupus erythematosus,

mixed connective tissue disease varies from clinically insignificant to

typically severe PM or DM in which myopathy dominates the clinical picture

anti-Ro, anti-La, anti-Sm, or anti-ribonucleoprotein (RNP) antibodies.

Differential DiagnosisDrug induced: statins, colchicine,

hydroxychloroquine, steroids, etoh, cocaine

HIVALSMyasthenia gravis Muscular dystrophiesInherited metabolic myopathiesAmyloid & Sarcoid myopathies

Work-upSerology: CK, CK-MB, AST, ALT,

adolase, ANA, anti-Jo1, anti-SRP, anti-Sm, anti-Ro

Utox, HIVMuscle biopsy+/- EMGsAge appropriate cancer screening

for those with dermatomyositis

TreatmentSteroids, PT/rehabMinimal data of long-term follow-up of

ptsPM: 50% were refractory to steroidsDM, 87% responded to steroids but 92%

flared when therapy was tapered. Overlap myositis: 89 to 100% responded

to steroids, depended on specific antibodies.

Methotrexate or Azathioprine

PrognosisDeterminants of prognosis:

the specific type of myositisdisease severitydelay in diagnosisCertain autoantibody profile

PM: least likely to respond to steroids

Overlap myositis: most likely to respond to steroids.