246. Inflammatory Myopathies

Question 1

Definition of Inflammatory Myopathy

Answer 1

Immune response directed against muscle, supporting stroma, or muscle as one of many tissues

Inflammation not always autoimmune

Question 2

Polymyositis

Signs, Labs

Answer 2

Symmetric Proximal > Distal Weakness
Occasional mild face weakness/dysphagia (swallowing problems)
Insidious onset
Myalgia
Pulm Involvement: ILD, ESP If ANTI-JO-1 POSITIVE - highly specific for ILD (F>M)
constitutional sx, polyarthralgias

High CK, ANA, high ESR/CRP, Possible Anti-Jo-1, EMG/biopsy abnormalities

Question 3

Polymyositis

Pathology, Tx

Answer 3

Path: inflammation around normal muscle fibers (CD8+ mediated), scattered necrosis, internal nuclei (instead of periphery), fiber size variability, multifocal

Tx: corticosteroids, azathioprine, MTX, IVIG, Rituximab (all take 6 mo for maximal effect)

Question 4

Dermatomyositis

Sx

Answer 4

F>M, children and adults
Proximal Weakness, Dysphagia
Skin: Sun-exposed Erythema, Heliotrope rash (purple around eyes), Gottron’s sign (Eczema on extensor surfaces), erythema periungal
ILD: 50% pts AntiJo1+!!!
MALIGNANCY 6-45% ASSOC!!!
Esophageal Disease, GI Vasculopathy, myocarditis

Question 5

Dermatomyositis

Path, Tx, Complication

Answer 5

Path: Humorally mediated (CD4+): membrane attack complex at normal appearing capillaries, perivascular inflammation, PERIFASCICULAR ATROPHY - PATHOGNOMONIC

Tx: Corticosteroids, Azathioprine, MTX, IVIG, Rituximab

C: MALIGNANCY (not in kids), ovarian cancer most assoc, need yearly screens for 2+ years

Question 6

Inclusion Body Myositis

Sx, Labs

Answer 6

M>F, 50+ y/o
DISTAL weakness, asymmetric (Quads -walking, wrist/finger flexors - shaving/makeup)
Very gradual, years for progression

Labs: CK mildly elevated, SENSORY NEUROPATHY, Anti-CN1A antibody SPECIFIC for IBM

Question 7

Inclusion Body Myositis

Path, Tx

Answer 7

P: CD8+ mediated but NO INFLAMMATION
RIMMED VACUOLES: contain beta-amyloid (Muscle Alzheimers)
Biopsy: LM apple-green birefringence

Tx: NO STEROIDS (not inflammatory)
Maybe IVIG but expensive

Question 8

Necrotizing Myopathy
(3 subtypes)

Answer 8

NO Inflammation, HIGH CKs
1. Statin Use: anti-HMG CoA Reductase Ab! focal necrosis of myocytes on biopsy, responds to immunotherapy (aggressive)

2. SRP Myopathy: HYPERACUTE WEAKNESS, anti-SRP Ab, more common in AA women, HIGH CK!, necrosis of muscle, responds to immunotherapy
3. Paraneoplastic: hidden/known cancer where antibodies cross over