What is the Difference Between Dermatomyositis and Polymyositis?
🆚 Go to Comparative Table 🆚Dermatomyositis and polymyositis are both autoimmune diseases that cause inflammation of the muscles, most commonly affecting the upper arms and thighs, resulting in weakness. However, there are some differences between the two conditions:
- Affected muscles: Polymyositis mainly affects the muscles, while dermatomyositis can cause skin lesions in addition to muscle inflammation.
- Skin involvement: Dermatomyositis is characterized by a skin rash, while polymyositis does not typically cause skin issues.
Both conditions are systemic disorders, which means they can affect other organs as well, such as the lungs, skin, and esophagus. The exact causes of dermatomyositis and polymyositis are not known, but they most often occur in people aged 31 to 60 and rarely occur in people younger than 18. Diagnosis and treatment of these conditions usually involve a combination of physical examinations, diagnostic tests, and medications that limit and reverse inflammation, allowing the muscles to heal and return to normal function.
Comparative Table: Dermatomyositis vs Polymyositis
Dermatomyositis (DM) and polymyositis (PM) are idiopathic inflammatory myopathies that share some common features, such as progressive symmetric proximal muscle weakness. However, they also have distinct differences, as shown in the table below:
| Feature | Dermatomyositis | Polymyositis |
|---|---|---|
| Clinical Presentation | Characteristic skin rash, Gottron's papules, and heliotrope rash | None |
| Muscle Weakness | Proximal muscle weakness, with dermatomyositis more likely to involve periorbital muscles | Proximal muscle weakness, without specific involvement of periorbital muscles |
| Age at Onset | Affects both children and adults, with an overall female/male ratio of about 2:1, average age at diagnosis of 40 years | Rare in childhood, most common time of presentation is between 45 and 60 years of age |
| Associated Diseases | Often associated with connective tissue diseases such as rheumatoid arthritis, scleroderma, systemic lupus erythematosus, Sjögren's syndrome, polyarteritis nodosa, and mixed connective tissue disease | Less likely to be associated with connective tissue diseases |
Despite their differences, both conditions are characterized by proximal muscle weakness and require similar treatments, such as corticosteroids and immunosuppressive agents. Further research is needed to better understand their etiologies, pathogenesis, and optimal treatment strategies.
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