Dermatomyositis and Polymyositis


Juvenile Dermatomyositis (JDM) and Polymyositis (JPM) are rare ‘autoimmune’ diseases. The immune system is a group of cells that usually protect the body from infection. In an autoimmune disease like JDM / JPM, the immune system attacks the body instead of protecting it. Both illnesses cause the muscles to become weak; weakness typically starts in the arms and legs. JDM (but not JPM) also affects the skin with a rash. The rash is usually on the face and knuckles but can occur on other parts of the body. In adults, DM and PM may be associated with cancer, but this complication is very rare indeed in children.

JDM is rare, affecting 3 or 4 in 1,000,000 children each year. JDM is more common than JPM. JDM can occur in children at any age, but typically presents between the ages of four and ten.


Last updated December 2016 by Dr Liza McCann and Prof Lucy Wedderburn, Juvenile Dermatomyositis Research Centre, UCL GOS Institute of Child Health, London, UK and Alder Hey Childrens NHS Foundation Trust.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

The onset of the condition may be sudden but usually develops over a longer period of time. Lethargy (tiredness) is often the first sign and young children may become miserable or irritable. Children may have a rash, often on the knuckles, hands, face and other parts of the body, including elbows, knees or ears. Sometimes the skin can break down causing ulcers or calcium can get deposited under the child’s skin. They may start to have difficulty doing things like climbing stairs or getting up from a sitting position due to muscle weakness. They may also have fever, joint pain, tummy ache and headaches.

What are the causes?

We do not know the exact cause but we think that these diseases are due to inflammation (redness / soreness) of the muscle and small blood vessels caused by cells of the immune system. We think that the immune system is triggered by infection or environmental factors (like sunlight) in people who carry genes that make them more prone to getting an autoimmune disease.

How is it diagnosed?

Doctors use a combination of symptoms (the things you tell us), examination (the things we see) and results of tests (such as blood tests and scans) to diagnose JDM / JPM. Electromyography (tests the electrical activity of nerves and muscles) and muscle biopsy may be used to help diagnosis or rule out other conditions.

How is it treated?

The progress of the disease is unpredictable and may include relapses (where symptoms appear to get better but reappear later). However, most children with JDM / JPM respond well to treatment, which usually includes steroids and other medications such as methotrexate, which work by reducing the activity of the immune system. Children also need physiotherapy and an exercise programme to help them regain strength in their muscles. Ideally children are looked after by a team of specialists who are used to caring for children with JDM/JPM.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Some research has shown that certain parts of our genetic make-up may make these conditions slightly more likely. However, these diseases are not ‘inherited’ and it is very rare to have two people with myositis in one family. JDM and JPM are more common in girls than boys.

Prenatal diagnosis
These conditions are extremely rare under one year and are not diagnosed before birth.

Is there support?

Myositis UK

Tel: 023 8044 9708

The Organisation is a National Registered Charity No. 327791. It provides information and support to individuals and their families affected by Dermatomyositis, Polymyositis, Inclusion Body Myositis and Juvenile Dermatomyositis. The Organisation holds an annual conference which is free for members, and has four Facebook groups. 

Group details last updated December 2016.

UK Juvenile Dermatomyositis Research Group


This website provides information for families and patients as well as information on research going on in the UK

Group details confirmed December 2016.

Back to A-Z Conditions