Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine (109 page)

INFLAMMATORY MYOPATHIES

Definition & epidemiology
(
JAMA
2013;305:183)
•
Polymyositis
(PM): T cell–mediated muscle injury → skeletal muscle inflam & weakness •
Dermatomyositis
(DM): immune complex deposition in blood vessels with complement

activation → skeletal muscle inflam. & weakness + skin manifestations

•
Inclusion body myositis
(IBM): T cell–mediated muscle injury, vacuole formation with

amyloid deposition → skeletal muscle inflam & weakness

• 10% of PM and 24% of DM a/w malignancy (typically adenocarcinomas, a/w more severe disease) (Curr Rheumatol Rep 2011;13:208) • PM/DM: onset typically 40s and 50s;
>
; DM also occurs in childhood • IBM: onset after age 50;
>
; often misdiagnosed as polymyositis
Clinical manifestations
(
Rheum Dis Clin N Am
2011;37:143)
•
Muscle weakness
: gradual (wks → mos), progressive and painless

DM/PM: proximal and symmetric; difficulty climbing stairs, arising from chairs, brushing hair; ± tenderness of affected areas; fine motor skills (eg, buttoning, writing) lost late

IBM: may be asymmetric and distal

•
Dermatologic
: may precede myositis by mos to yrs (uncommon for converse)

erythematous rash
on sun-exposed skin: neck & shoulders (shawl sign), face, chest

heliotrope rash
(purplish discoloration) over upper eyelids ± periorbital edema

Gottron’s papules
(in >80% & pathognomonic): violaceous often scaly areas symmetrically over dorsum of PIP and MCP joints, elbows, patellae, medial malleoli

subungual erythema, “mechanic’s hands” (skin cracks on digits), pruritus

dermatologic features w/o myositis=
DM sine myositis
(amyopathic DM) in 10–20%

• Polyarthralgias or polyarthritis: usually early; nonerosive; small joints > large joints • Raynaud’s (30%, DM and overlap CTD) w/ dilatation & dropout of nailbed capillaries •
Visceral involvement
(J Rheumatol 2009;36:2711)

pulmonary
: acute alveolitis; ILD; respiratory muscle weakness; aspiration

cardiac
(33%): often asx; conduction abnl; myo/pericarditis; HF uncommon; ↑ CK-MB/Tn

GI
: dysphagia, aspiration

•
Antisynthetase syndrome
(PM > DM): fever, ILD, Raynaud’s, mechanics hands, arthritis • Ddx: drug-induced myopathy (statins, cocaine, steroids, colchicine); infxn (HIV, EBV, CMV); metabolic (hypothyroid, hypo-K, hypo-Ca); neuromuscular dis. (eg, myasthenia gravis); glycogen storage disease; mitochondrial cytopathy; muscular dystrophy
Diagnostic studies

• ↑
CK
(rarely >100,000 U/L), aldolase, SGOT and LDH; ±↑ ESR & CRP

• Autoantibodies:
ANA (>75%),
RF (33%)

anti-Jo-1
(25%): most common specific Ab; a/w antisynthetase syndrome

myositis antibody panel may assist in prognosis (anti-Mi-2 better, anti-SRP worse)

•
EMG
: ↑ spontaneous activity, ↓ amplitude, polyphasic potentials with contraction •
Muscle biopsy
: all with interstitial mononuclear infiltrates, muscle fiber necrosis, degeneration & regeneration (required for definitive diagnosis)

PM: endomysial inflam. (CD8 T cells) surrounds non-necrotic fibers, ↑ MHC class I

DM: perimysial, perivascular inflam (B & CD4 T cells), complement in vessels

IBM: same as PM with eosinophilic inclusions and rimmed vacuoles (EM)

Treatment
(PM & DM, no effective treatment for IBM) (Autoimmun Rev 2011;11:6)
•
Steroids
(prednisone 1 mg/kg); MTX or AZA early if mod/severe or taper fails (2–3 mo) • For resistant (30–40%) or severe disease: AZA/MTX combo, IVIg (DM ± PM), rituximab, MMF, cyclophosphamide (esp. if ILD or vasculitis) • IVIg w/ pulse steroids acutely for life-threatening esoph or resp muscle involvement • ✓ for occult malignancy (esp. if DM); monitor respiratory muscle strength with spirometry

SJÖGREN’S SYNDROME

Definition & epidemiology

• Chronic dysfxn of
exocrine glands
(eg, salivary/lacrimal) due to lymphoplasmacytic infiltration. Extraglandular manifestations common in primary form.

• Can be primary or secondary (a/w RA, scleroderma, SLE, PM, hypothyroidism, HIV)

• More prevalent in
than
; typically presents between 40 & 60 y of age
Clinical manifestations