Inflammatory Myopathies

Question 1

inflammatory myopathies - examples

Answer 1

1. polymyositis (PM)
2. dermatomyositis (DM)
3. inclusion body myositis (IBM)

Question 2

inflammatory myopathies - epidemiology

Answer 2

*polymyositis & dermatomyositis:
-childhood (5-15 yo) and midlife (30-60 yo)
-females > males

*inclusion body myositis:
-age > 50
- males > females

Question 3

evaluation of weakness in inflammatory myopathies

Answer 3

*watch how they do tasks: stand from a seated position without using arms, lift hands above head, difficulty walking
*objective strength testing:
-flexors and extensors of the upper and lower extremities
-scale to standardize weakness (0 = no contraction; 5 = normal strength)

Question 4

polymyositis (PM) & dermatomyositis (DM) - clinical presentation

Answer 4

*PROXIMAL muscle weakness:
-subacute, symmetric
-difficulty getting out of chair unassisted, reaching above their head
*dysphagia
*interstitial lung disease
*skin:
-rashes in dermatomyositis
-periungal abnormalities
-calcinosis

Question 5

rashes in dermatomyositis

Answer 5

1. Heliotrope rash (violaceous rash around the eyes)
2. Gottron’s papules (knuckles)
3. Gottron’s sign (elbows & knees)
4. Shawl/V sign (red rash on upper back or in a V neck shirt pattern)
5. Holster sign (red rash on lateral thigh)

Question 6

periungual abnormalities in dermatomyositis (and polymyositis?)

Answer 6

*cuticular hypertrophy
*abnormal nailfold capillaries (particularly in dermatomyositis)

Question 7

calcinosis cutis

Answer 7

*calcium deposits in the skin
*more common in dermatomyositis
*more common in children (rare in adults)

Question 8

anti-synthetase syndrome

Answer 8

*several antibodies associated with syndrome: Jo-1 antibody (anti-histidyl-tRNA synthetase)
*specific features:
-arthritis, Raynaud’s phenomenon, mechanics hands (dry cracked skin on thumb and first finger)
*aggressive interstitial lung disease:
-check PFTs & HRCT scan

Question 9

inclusion body myositis - clinical presentation

Answer 9

*unique pattern of weakness:
-often asymmetric
-slowly progressive (over years)
-DISTAL INVOLVMENT (wrist flexors, ankle dorsiflexors, distal finger flexors)
*still can have typical muscle group involvement
*more likely to have dysphagia

Question 10

inflammatory myopathies - lab findings

Answer 10

*elevated CK (10-20x upper limit of normal in PM/DM; tends to be only mild elevation in IBM)
*LFTs: AST/ALT elevation
*inflammatory markers elevated
*ANA positive often
*myositis-specific antibodies:
-anti synthetase antibodies (anti-Jo-1)
-myositis antibody panel

Question 11

inflammatory myopathies - other testing

Answer 11

*EMG/NCS:
-helps differentiate nerve vs. muscle, inflammatory vs. non-inflammatory, help find a site for biopsy
*MRI:
-can look for inflammation, infection, etc; help find site for biopsy
*muscle biopsy = gold standard

Question 12

polymyositis - biopsy findings

Answer 12

* endomysial infiltrates (within the fascicle)
*CD8+ mediated
*MHC class I expression

Question 13

dermatomyositis - biopsy findings

Answer 13

*perifascicular (perimysium) infiltrate
*atrophy
*CD4+ cells

Question 14

inclusion body myositis - biopsy findings

Answer 14

*endomysial infiltrates, CD8+
*rimmed vacuoles
*IBM difficult to find - average of 2-3 biopsies before positive

Question 15

inflammatory myopathies - malignancy association

Answer 15

*relative risk for cancer;
-dermatomyositis: 2-4x risk; polymyositis: 2x risk
*most cancers within 2 years of myositis diagnosis
*adenocarcinomas are over-represented, esp ovarian carcinoma
*risk factors:
-age > 50, male gender, severe rash
-certain antibody association (some protective, some increase risk)

Question 16

dermatomyositis & polymyositis - treatment

Answer 16

*high dose steroids
*some can taper without issue, others need steroid-sparing agent
*consider other clinical features (esp. interstitial lung disease)

Question 17

inclusion body myositis - treatment

Answer 17

*poor response to medical therapy (steroids do more harm than good)
*supportive tx with physical therapy

Question 18

ddx for inflammatory myopathies

Answer 18

*endocrine disorders (thyroid)
*toxins
*infections, amyloid, paraneoplastic
*medication induced
*other rheumatic disease
*muscular dystopathies
*metabolic myopathies (disorders of metabolism, mitochondrial myopathies)
*muscle channelopathies

Question 19

ddx of elevated CK

Answer 19

*an elevated CK does not necessarily equal myositis; CK is very non-specific; many things can cause elevated CK, including:
1. physical trauma or muscle stress
2. drugs (statins, EtOH, amphetamine, heroin, AZT)
3. muscle (noninflammatory myopathies, MI, malignant hyperthermia, etc)

Question 20

workup for inflammatory myopathies

Answer 20

*good clinical history and exam
*for myositis, should be checking: CK, ESR/CRP, CBC, CMP
*check TSH
*UDS, EtOH level if clinically appropriate
*medication evaluation: stop potentially offending medications

Question 21

statins & muscles

Answer 21

*most often myalgias
*only about 1% with weakness
*CK can be elevated but normally only slightly
*always stop statin and see if symptoms resolve and CK improves
*seen more frequently with statins that are metabolized through CYP3A4
*rarely cause a necrotizing myopathy