Juvenile dermatomyositis

Muscle inflammation in juvenile dermatomyositis produces muscle weakness predominantly in the arms and thighs. This is known as proximal or waisted muscle weakness. This causes the child to have difficulty performing basic activities such as going up/down stairs, getting dressed, getting out of bed or simply referring to it as tiredness.

Muscle weakness is usually present at diagnosis or appears during the course of the disease, although it is rare once immunosuppressive treatment is initiated.

Axial muscle involvement (neck, abdomen) is common and is usually the last to recover. Sometimes the muscle inflammation is so intense that it can produce a sensation of stiffness or numbness. 

In addition to inflammation of the muscles that are responsible for moving our body, muscle inflammation can occur at other levels with the consequent symptomatology:

• The involvement of the pharyngeal muscles can cause difficulty in swallowing both liquids and solids. This may manifest as coughing with swallowing, caused by passage of food contents into the airway, or choking, due to difficulty propelling the food bolus. The passage of food contents into the airway can lead to pulmonary infection (aspiration pneumonia).
• The affectation of the palate muscles can produce changes in the tone of the voice (nasal voice).
• Inflammation of the chest muscles may make inspiration difficult, resulting in shortness of breath due to the inability to draw air into the lungs. Therefore, the patient may have difficulty in breathing due to the muscle weakness itself without pulmonary involvement by the disease.

Initially, if the muscular weakness is not important, the child may stop running, jumping, adapting his/her play. Only when it is moderate-severe will we notice that he/she cannot get out of bed, go up and down stairs... Sometimes, this limitation to perform the usual activities causes frustration with alteration of the character and decrease of the mood.  

In addition to muscle inflammation, there may be inflammation of the joints, which will produce an increase in their size, usually accompanied by predominantly post-repositional stiffness. Joint involvement may further impair the patient's mobility.