Dermatomyositis is an autoimmune inflammatory myositis.
There is a recognized female predilection. It has a bimodal age of presentation depending on the variant:
- juvenile dermatomyositis (JDM): affects children and tends to be more severe
- adult dermatomyositis (ADM): typically affects adults around the age of 50
The classic presentation is that of a symmetrical proximal myopathy with associated dermatological changes which includes a dusky-red rash over the face, arms, hands, legs and other features (e.g. Gottron papules). Dysphagia, myalgia, fever and weight loss are other features 7.
There is cell-mediated injury targeted at striated muscle with resultant atrophy, edema, coagulation necrosis, fibrosis and calcification.
- elevated muscle enzymes (e.g. CK)
- elevated muscle specific antibodies
- hypomyopathic dermatomyositis
- clinically amyopathic dermatomyositis (CADM) / amyopathic dermatomyositis
- interstitial lung disease 2: typically gives a patchy and subpleural consolidation with parenchymal bands
- internal malignancy 1: can occur as part of a paraneoplastic syndrome (e.g. lung cancer)
- typically shows dystrophic calcification in muscles and soft tissues (calcinosis universalis)
- sheet-like although at least four patterns have been described with childhood dermatomyositis 4
- classically seen affecting the thigh regions
- chest radiograph may show diaphragmatic elevation
- may show disordered peristalsis involving the upper esophagus i.e. the portion supplied by skeletal muscle
- T2: generally hyperintense signal throughout the affected muscles; calcific areas may be low signal; perimuscular edema may additionally appear as high signal; signal intensity may return to normal after treatment 4
General imaging differential considerations include:
- polymyositis: does not affect the skin
MRI T2-weighted sequences are useful to guide muscle biopsy:
- areas of edema related to the active inflammatory process
- non-specific end-stage fatty atrophic muscle should be avoided
Further imaging in the form of a contrast-enhanced CT of the chest, abdomen and pelvis may be undertaken to exclude an associated primary malignancy.
- 1. Kubo M, Ihn H, Yamane K et-al. Serum KL-6 in adult patients with polymyositis and dermatomyositis. Rheumatology (Oxford). 2000;39 (6): 632-6. doi:10.1093/rheumatology/39.6.632 - Pubmed citation
- 2. Mino M, Noma S, Taguchi Y et-al. Pulmonary involvement in polymyositis and dermatomyositis: sequential evaluation with CT. AJR Am J Roentgenol. 1997;169 (1): 83-7. AJR Am J Roentgenol (abstract) - Pubmed citation
- 3. Akira M, Hara H, Sakatani M. Interstitial lung disease in association with polymyositis-dermatomyositis: long-term follow-up CT evaluation in seven patients. Radiology. 1999;210 (2): 333-8. Radiology (full text) - Pubmed citation
- 4. Blane CE, White SJ, Braunstein EM et-al. Patterns of calcification in childhood dermatomyositis. AJR Am J Roentgenol. 1984;142 (2): 397-400. AJR Am J Roentgenol (abstract) - Pubmed citation
- 5. Hernandez RJ, Sullivan DB, Chenevert TL et-al. MR imaging in children with dermatomyositis: musculoskeletal findings and correlation with clinical and laboratory findings. AJR Am J Roentgenol. 1993;161 (2): 359-66. AJR Am J Roentgenol (abstract) - Pubmed citation
- 6. Tomasová studynková J, Charvát F, Jarosová K et-al. The role of MRI in the assessment of polymyositis and dermatomyositis. Rheumatology (Oxford). 2007;46 (7): 1174-9. doi:10.1093/rheumatology/kem088 - Pubmed citation
- 7. Marvi U, Chung L, Fiorentino DF. Clinical presentation and evaluation of dermatomyositis. Indian J Dermatol. 2012;57 (5): 375-81. doi:10.4103/0019-5154.100486 - Free text at pubmed - Pubmed citation