Dermatomyositis is an autoimmune inflammatory myositis.
There is a recognised 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 proximal, symmetrical motor weakness with cutaneous changes. Dysphagia, myalgia, fevers, and loss of weight are other features 7.
There is cell-mediated injury targeted at striated muscle with resultant atrophy, oedema, coagulation necrosis, fibrosis and calcification.
- elevated muscle enzymes (e.g. CK)
- elevated muscle specific antibodies
- 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 oesophagus i.e. the portion supplied by skeletal muscle
- T2: generally hyperintense signal throughout the affected muscles; calcific areas may be low signal; perimuscular oedema 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 oedema related to the active inflammatory process
- nonspecific 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