1. Idiopathic Inflammatory Myopathies

2. Idiopathic Inflammatory Myopathies Major forms:
Polymyositis
Dermatomyositis
Inclusion Body Myositis

3. Classification of Idiopathic Inflammatory Myopathies
Polymyositis and Dermatomyositis
Polymyositis, primary, adult
Dermatomyositis, primary, adult
Myositis with malignancy
Juvenile dermatomyositis
Myositis in connective tissue diseases
Inclusion body myositis
Other: Granulomatous, Eosinophilic, Localized, Proliferative, Orbital

4. Idiopathic Inflammatory Myopathies
Incidence PM/DM: cases/100K/yr
Less than frequency of scleroderma which is less than for lupus
Prevalence: 3-10 cases/100,000
Children: DM>PM>IBM
Adult<50: PM>DM>IBM
Using clinical definition of PM
Adult>50: IBM>PM>DM
Malignancy: DM>PM>IBM
Peak: PM/DM yrs; IBM older
Juvenile peak approx 10 y
PM/DM F>M; IBM M>F

5. Presentation of Idiopathic Inflammatory Myopathies
Proximal muscle weakness
Most common presenting muscle-related complaint
Elevated muscle enzymes
CK, aldolase, AST/ALT
Myalgia
Dermatologic findings of DM
Gottron’s, Heliotrope, Other
Other extramuscular features
ILD, Arthritis, Dysphagia
Most patients come to medical attention due to weakness consistent with myopathy. Most have elevated enzymes at presentation, but usually not the presenting feature. Similarly, Myalgia is less often the main symptom, but present in 50%. For some patients, skin manifestations are the presenting feature and may predominate. Some patients present with extramuscular manifestations.

6. Traditional PM/DM Criteria for Diagnosis:
Weakness
Symmetric proximal muscle weakness
Enzymes
Muscle enzymes elevated
Electromyography
Myopathy with normal nerve conduction
Muscle Biopsy
Inflammation
Skin changes of DM
Gottron’s papules, heliotrope, other

7. Traditional PM/DM Criteria for Diagnosis:
Any 4 = Definite
Any 3 = Probable
Any 2 = Possible
Exclusions:
Family History
Slow progression
Other myopathies
Weakness
Enzymes
EMG
Muscle Biopsy
Skin changes

8. Additional Diagnostic Considerations
Magnetic Resonance Imaging
Autoantibodies
Evidence of inflammatory/rheumatic disease

9. Muscle Weakness in IIM Proximal, Symmetrical, Upper & lower
Pelvic, shoulder girdles, neck flexors
Dysphagia
Respiratory involvement
Subacute onset
Muscle weakness vs Fatigue
The muscle weakness of myositis is typical of myopathies. It generally involves skeletal muscle, more proximal than distal. Dysphagia can occur due to involvement of muscles of swallowing. Dysphagia and respiratory muscle involvement are risk factors for complications.

10. Muscle Weakness in IIM Signs of concern: Potential for Complication
Dysphagia
Respiratory Muscle Weakness
Severe Weakness
Can lead to aspiration pneumonia or respiratory failure.

11. Manual Muscle Testing Manual resistance against active contraction
Rating scale of 1-5
Subjectivity
Pain, Fatigue and Effort can confound

12. Activities to Assess Strength
Timed stands from chair (arms folded)
Squatting
Sit from supine
Stand on heels and toes
Getting onto exam table.
Timed 50-foot walk
Lifting head off exam table

13. Laboratory Assessment of Muscle Injury
Creatine Kinase
Aldolase
LDH
AST/ALT
Troponin
Myoglobin
Levels of enzymes and markers can vary with disease activity and thus can be used for assessing disease activity as well as for diagnosis.
CK is most sensitive. The other markers are often used when CK is normal or not reflective of disease activity, or to support the significance of the CK result.

14. ELECTROMYOGRAPHY in Inflammatory Myopathy
Myopathic Potentials
Low Amplitude
Short Duration
Polyphasic
Increased Spontaneous Activity
Fibrillations, Positive Sharp Waves
Increased Insertional Activity
Normal Nerve Conduction

15. Electromyography Normal Polyphasic Myopathic
Goetz: Textbook of Clinical Neurology, 2nd ed., Copyright © 2003 Elsevier
Polyphasic
Myopathic

16. Electromyography Resting Interference pattern
Goetz: Textbook of Clinical Neurology, 2nd ed., © 2003 Elsevier