Dermato & Polymyositis

Exam Cram

• Dermatomyositis and polymyositis are inflammatory myositis

• Polymyositis presentation: proximal myopathy, sob

• Dermatomyositis presentation: rash- sun exposed, violet + proximal myopathy

• Associated with ILD

Outline

Background 

• Polymyositis and dermatomyositis are where the immune system attacks the patients muscles

• Two peaks of onset: 40yrs and 60yrs

• Associations: pulmonary fibrosis; malignancy of lung, breast, female genital tract, stomach & rectum

Assessment

History:

• 3 month: progressive muscle weakness- shoulders & hips 

• 40-60F

• SoB, dysphagia

Examination:

• Proximal lung weakness

• Rash- violet, sun exposure distribution, heliotrope (dermatomyositis)

• Bilateral inspiratory crackles 

Investigations

• Raised ESR & CRP

• CK raised significantly

• Anti Jo: specificity 20% (polymyositis)

• Anti-Mi (highly specific, 25% sensitive)

• Muscle biopsy

• EMG

Diagnosis 

Polymyositis Diagnostic criteria: symptoms without rash + biopsy

Dermatomyositis diagnostic criteria: symptoms with rash + biopsy

• Electromyography and raised CK helpful

• Anti Jo antibodies not useful as not sensitive or specific

Differentials: Muscular dystrophy

Management

Acute

1. Prednisolone (acute)

2. Azathioprine (steroid sparing, LT)

3. Cyclophosphamide or cyclosporin if evidence of lung disease

4. Rituxumab

References and Resources

Created in 2024.