26th January 2024

Presentation

Dermatomyositis presents with proximal, symmetrical muscle weakness, elevated muscle enzymes and distinctive cutaneous findings. Myalgia is common during the active phase and respiratory muscle, and there may sometimes be myocardial and respiratory muscle involvement and signs of dysphasia. 

Characteristic cutaneous findings include a heliotrope rash, a violaceous, oedematous rash affecting the eyelids and Gottron’s papules over the MCP and PIP joints and extensor surfaces. Other less common skin presentations include calcinosis cutis, poikiloderma, periungual telangiectasias and cuticular hypertrophy. 

Polymyositis presents with similar muscle weakness as dermatomyositis. However, there are no characteristic skin changes, making it more difficult to diagnose clinically. The hip extensors are often a severely affected muscle group, causing difficulty in climbing stairs and standing from a seated position. It is defined by the presence of anti-synthetase autoantibodies and features such as interstitial lung disease, inflammatory myopathy and small joint symmetrical polyarthritis. 

Inclusion body myositis tends to have a more insidious onset, with the average onset of symptoms 5 years prior to diagnosis. There is asymmetric, distal muscle involvement, such as finger flexors and forearm flexors and as such, these patients may complain of weakness in grip strength and difficulty in doing tasks such as opening jars. Myalgia, muscle atrophy and dysphagia can occur but not as commonly.

Image Source: Wikimedia Commons (2022). Dermatomyositis10, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/a/a1/Dermatomyositis10.jpg (Accessed: 10 July  2022).

Image Source: Wikimedia Commons (2022). Dermatomyositis2, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/7/7b/Dermatomyositis2.jpg (Accessed: 10 July  2022).