Dermatomyositis: Muscle Histology

1. Dermatomyositis:Muscle Histology Perifascicular atrophy and inflammation

2. Dermatomyositis Muscle Histology Perifascicular atrophy

3. Vascular Hypothesis: Complement-mediated microangiopathy Deposition of complement (MAC) and antibody Reduced muscle capillaries Ischemic damage to muscle Nailfold capillary changes Cutaneous ulcerations Intestinal perforation Pathogenesis of Dermatomyositis

4. Histopathology of DMDalakas: Rheum Dis Clin 28:779,2002 Normal capillaries Reduced, abnormal capillaries

5. Nailfold Changes Figure from American College of Rheumatology slide collection

6. Nailfold Capillary Changes Normal Sclero-derma Adult DM JDM Narrow, straight, regular capillaries are normally seen. In scleroderma and DM, there is dilation, distortion, loss. (Figure and slide note caption from American College of Rheumatology slide collection)

7. Interferon Hypothesis type 1 interferons (α,ß) cause capillary, muscle fiber, and skin injury Interferon-producing cells in muscle Increase in type 1-interferon inducible proteins and mRNA transcripts in muscle Tubuloreticular inclusions in muscle capillaries Pathogenesis of Dermatomyositis

8. Histologic Patterns Dermatomyositis:Perifascicular Atrophy Polymyositis: Endomysial Infiltration

9. Gottron’s papules over fingers Gottron’s sign over extensor surfaces Heliotrope sign Erythematous rash Poikiloderma Photosensitivity Nailfold changes Mechanic’s hands Calcinosis Cutaneous ulcerations Cutaneous Features of Dermatomyositis

10. Dermatomyositis: Gottron’s Figure and caption from American College of Rheumatology slide collection

11. Dermatomyositis: Gottron’s See slide note for caption. Figure and caption from American College of Rheumatology slide collection

12. Dermatomyositis: Gottron’s Papules

13. Dermatomyositis: Gottron’s Papules

14. Dermatomyositis: Heliotrope Sign

15. Dermatomyositis: Heliotrope Figure and caption from American College of Rheumatology slide collection

16. Dermatomyositis: Rash Figure and caption from American College of Rheumatology slide collection

17. Dermatomyositis: Erythematous Rash

18. Dermatomyositis: Poikiloderma

19. “Mechanic’s Hands” From Miller FW. Myositis-specific autoantibodies: touchstones for understanding the inflammatory myopathies. JAMA 1993;270:1846-1849. See slide note for caption. Figure and caption from American College of Rheumatology slide collection.

20. Dermatomyositis: Calcinosis See slide note for caption. Figure and caption from American College of Rheumatology slide collection.

21. Cutaneous Ulceration

22. Dermatomyositis: Cutaneous Ulcerations

23. Additional Diagnostic Considerations • Magnetic Resonance Imaging and Spectroscopy • Autoantibodies (ANA, Specific autoantibodies) • Evidence of inflammatory/rheumatic disease (Fever, ESR, Arthritis, Raynaud's, ILD, vascular disease)

24. MAGNETIC RESONANCE IMAGING PM and DM • Can detect inflammation when biopsy, enzymes, and/or EMG are normal. • Can be used for: • Establishing diagnosis • Excluding myositis • Assessing inflammatory activity • Persistent weakness • Persistent enzyme elevation • Can identify site of active inflammation to direct biopsy

25. MAGNETIC RESONANCE IMAGING in IIM • Active disease best shown by T2-weighted images, reflecting increased water/edema. • Fatty replacement and atrophy also seen • Thighs most often studied • May be focal • Changes with disease activity

26. Dermatomyositis: Thigh (MRI) Figure and caption from American College of Rheumatology slide collection