What is the Difference Between Dermatomyositis and Polymyositis

The key difference between dermatomyositis and polymyositis is that dermatomyositis is an inflammatory myopathy that mainly causes symmetric proximal muscle weakness and skin rash, while polymyositis is an inflammatory myopathy that mainly causes symmetric proximal muscle weakness.

Inflammatory myopathy is a condition that involves chronic muscle inflammation, muscle weakness, muscle pain, and in some cases, rashes in the skin. The two main inflammatory myopathies are dermatomyositis and polymyositis. The common causes of these inflammatory myopathies include infection, muscle injury due to medicine, inherited diseases that affect muscle function, electrolyte disorders, and thyroid disease. Moreover, people of all ages are affected by these main inflammatory myopathies. But the peak time to get these diseases is ages 5 to 10 in children and 40 to 50 in adults. In addition, women are more affected than men by these inflammatory myopathies.

CONTENTS

1. Overview and Key Difference
2. What is Dermatomyositis  
3. What is Polymyositis
4. Similarities – Dermatomyositis and Polymyositis
5. Dermatomyositis vs Polymyositis in Tabular Form
6. Summary – Dermatomyositis vs Polymyositis

What is Dermatomyositis?

Dermatomyositis is a rare inflammatory myopathy condition that causes muscle inflammation. It is mainly characterized by symmetric proximal muscle weakness and skin rash (red or purple rash on sun exposure area)), extramacular manifestations such as esophageal dysfunction and interstitial lung disease, red or purple swelling of the upper eyelids, stuff, pale and painful joints, scaly, rough, dry skin, swollen, red areas around fingernails, calcinosis, trouble swallowing and voice changes, tiredness, fever, weight loss, muscle aches, and difficulty rising from a chair or getting out of bed due to weakness. Moreover, dermatomyositis is also strongly associated with malignancies in adults. The causes of dermatomyositis may include inheriting abnormal genes, cancer in older people, autoimmune disease, infections, medications, or any environmental exposure in the environment.

Dermatomyositis can be diagnosed with a medical history, physical examination, blood tests, electromyogram (EMG), MRI, and skin or muscle biopsy. Furthermore, treatment options for dermatomyositis include physical therapy, skin treatment (anti-inflammatory steroid creams), anti-inflammatory medications (steroids drugs and corticosteroids), immunosuppressive drugs, immunoglobulins, and surgery.

What is Polymyositis?

Polymyositis is an inflammatory myopathy that is characterized by chronic muscle inflammation. It is accompanied by mainly symmetric proximal muscle weakness and affects skeletal muscle on both sides of the body. The exact cause of polymyositis is still not known. However, autoimmune diseases such as lupus, rheumatoid arthritis, Sjogren’s syndrome, and scleroderma trigger this condition. Moreover, the symptoms of polymyositis may include muscle pain and stiffness, muscle weakness in the abdomen, shoulders, upper arms and hips, joint pain and stiffness, difficulties in swallowing, and irregular heart rhythms.

Polymyositis can be diagnosed through physical and clinical examination, blood tests, electromyography, MRI, and muscle biopsy. Furthermore, treatment options for polymyositis may include medications to control muscle inflammation (corticosteroids, corticosteroid-sparing agents, and rituximab), physical therapy, speech therapy, dietetic assessment, and surgical and other procedures (giving intravenous immunoglobulin).

What are the Similarities Between Dermatomyositis and Polymyositis?

• Dermatomyositis and polymyositis are the two main inflammatory myopathies.
• Both conditions are rare conditions.
• Moreover, they are chronic inflammatory conditions.
• They are more common in ages 5 to 10 in children and 40 to 50 in adults.
• Both conditions are more common in women than men.
• They have similar symptoms, such as muscle weakness, muscle aches, joint pain, and stiffness.
• Both conditions can be diagnosed through physical examination, blood tests, and imaging tests such as MRI.
• They are treated through anti-inflammatory medications and surgeries.

What is the Difference Between Dermatomyositis and Polymyositis?

Dermatomyositis is an inflammatory myopathy that causes symmetric proximal muscle weakness and skin rash, while polymyositis is an inflammatory myopathy that causes symmetric proximal muscle weakness. Thus, this is the key difference between dermatomyositis and polymyositis. Furthermore, dermatomyositis causes swelling and tenderness in muscles as well as the skin, while polymyositis causes swellings and tenderness only in muscles.

The following table summarizes the difference between dermatomyositis and polymyositis.

Summary – Dermatomyositis vs Polymyositis

Inflammatory myopathy is a condition that involves chronic muscle inflammation, muscle weakness, muscle pain, and occasional skin rashes. Dermatomyositis and polymyositis are the two main inflammatory myopathies. Dermatomyositis mainly causes symmetric proximal muscle weakness and skin rash. Polymyositis mainly causes symmetric proximal muscle weakness. So, this summarizes the difference between dermatomyositis and polymyositis.

Reference:

1. “Dermatomyositis.” Johns Hopkins Medicine.
2. “Polymyositis: Symptoms, Causes, Diagnosis, Treatment, Prognosis.” WebMD.

Image Courtesy:

1. “Dermatomyositis” By Elizabeth M. Dugan, Adam M. Huber, Frederick W. Miller, Lisa G. Rider – Dermatology  (CC BY-SA 3.0) via Commons Wikimedia
2. “Polymyositis HE” By Jensflorian – Own work (CC BY-SA 3.0) via Commons Wikimedia