What are the symptoms of JDM ?

The main symptoms of JDM are muscle weakness, muscle pain, skin rashes, tiredness, irritability and fever. Some children can also have joint pains.

Muscle weakness and muscle pain

The muscles that are mostly affected are those near the central part of the body: the upper arms, the thighs, the neck and the trunk itself. Other muscles can become weak and children can have difficulty swallowing, or develop changes in their voice. Occasionally there is inflammation in the gut, which can cause bowel problems. Children with JDM can have difficulty getting up from bed, climbing stairs and getting up from the floor or from a chair. Walking and running can become challenging and exhausting. Muscle weakness can be assessed by doctors using specific outcome measures such as the Childhood Muscle Assessment Score ( CMAS.pdf ) and the MMT8 ( MMT8.pdf ). Apart from the weakness, children can complain of muscle pain because of the inflammation in their muscles.

Skin rash

The skin rash in JDM usually occurs on the face, knuckles, elbows, knees and ankles. The rash may appear before, after or at the same time as the muscle weakness. Sometimes the rash is so faint that it is not noticeable. Rashes can be photosensitive, that means that they can become worse in sunlight. The facial rash appears as a red purplish colour on the eyelids and cheeks; whereas it looks like red dry skin patches over the knuckles, elbows and knees. The fingernails and the nailbeds can show a pinkish colour as well. The following is a description of common rashes or other skin changes associated with JDM:

On the eyelids the rash appears as a red, purplish colour. This is called a ‘heliotrope rash.’
On the face, the rash appears as a reddened area on both cheeks and can cross the nose. This is called a ‘malar rash.’
Across the knuckles, elbows and knees, the rash looks like red / violet, dry skin patches. These are called ‘Gottron’s patches.’
The tiny blood vessels at the base of the fingernails may turn a pinkish colour or become more obvious. These are called ‘nail-fold capillary changes.’
Children may get swelling to the face or body, particularly around the eyes, due to watery fluid building up in the tissues. This is called oedema and when it occurs across the eyes it is called ‘peri-orbital oedema’.
Some children can develop small hard lumps under the skin or in the muscle that are due to calcium being deposited. This is called ‘calcinosis.’ These lumps can break through the skin (ulcerate) and leak a thick milky white fluid (calcium). If this happens, there is a chance of the lumps becoming infected. Calcinosis can be a sign of active disease or ongoing inflammation. These lumps are more common when the disease has been there for a long time. This is a sign that the disease needs aggressive treatment.
Sometimes fatty tissue can waste away in JDM. This is called lipodystrophy.

Fatigue

Children with JDM can tire easily and sometimes can only walk short distances. Exercise, like walking or running, may become increasingly difficult. Children may need to rest often and lack the energy for normal activities. It can become difficult for children to keep up with friends. Concentration and memory may also be affected when the illness is active

Irritability

You may notice your child seems quite irritable and their behaviour may become more difficult than normal. This symptom is commonly seen in children with active disease, particularly in younger ones.

Fever

Sometimes, children with JDM run low-grade fevers, which can be at night.

What are other possible manifestations ?

The following symptoms of JDM are less common, nonetheless important to understand:

Ulcers

Ulcers can occur in the skin and can look like sores within the skin rash. They can be deep or on top of the skin and they also range in size. The ulcers can be painful, but will usually heal with treatment.

Contractures

In some children, the inflamed muscles become tight and shorten (called contractures). This leads to difficulties in fully straightening the affected arm or leg: the elbows and knees tend to be in a fixed bent position and this can affect the movements of the arms or legs. Contractures can occur due to lack of movement as well.

Joint pain and sometimes joint swelling and stiffness

Both large and small joints can be inflamed in JDM. This inflammation can cause swollen joints as well as pain and difficulty in moving the joint. This inflammation responds well to treatment and it is uncommon for it to result in damage to the joints.

Abdominal pain or tummy ache

Some children have problems with their bowels. These can include tummy aches, constipation and occasionally severe abdominal problems if the blood vessels of the gut become affected.

Breathing problems

Breathing problems (such as cough and shortness of breath) may occur because of muscle weakness or because of inflammation in the lungs.

Other symptoms

Some children with JDM show tightness of the skin and their fingers can change colour in the cold (this is called Raynaud’s phenomenon); some of these problems can happen in other diseases as well, like a condition called lupus.

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