Myositis, or inflammatory muscle disease, is a immune system-driven, inflammatory muscle disease that leads to muscle weakness. This condition affects large muscles around shoulders and pelvic girdle and thighs.

Typical symptoms involve:

• Muscle weakness with difficulty climbing stairs and getting out of chairs

• Little or no pain in the muscles

• Breathing difficulties

• Cough after eating or choking sensation

Myositis is grouped into two distinct conditions:

• Polymyositis

• Dermatomyositis

There are distinct clinical and histological features that distinguish these two conditions.

There are other types of muscle disease that create muscle weakness to include congenital syndromes, metabolic muscle diseases and other. Various medications can create muscle weakness.

Dermatomyositis is a type of inflammatory muscle disease that also manifests with rashes . Rash typically involves skin around eyes, called heliotrope rash, skin of the arms and hands called Gottron's papules and around the neck in a distinct shawl like distribution.

Muscle biopsy in both inflammatory muscle diseases show specific changes with infiltration by white blood cells called lymphocytes. Muscle biopsy will distinguish both conditions.

If untreated, myositis leads to irreversible damage to the muscle tissue and chronic muscle weakness .

There is an increased risk of malignancy associated with both conditions and a careful history and physical exam with attention to appropriate health screenings should be done at the time of the diagnosis.

Diagnosis is made in the basis of clinical features, abnormal blood work, mainly elevated CPK and abnormal signal on EMG exam and specific changes on the muscle biopsy. A specialized antibody testing can help stratify patients risk for certain complications i.e. lung involvement .

Sometimes, MRI of the thigh is done to localize the best site of the muscle biopsy since inflammation can attack only certain muscles.

Treatment involves use of immunosuppressive medications. Steroids, disease-modifying medications, and biologics are being used.

Fast Facts

• Muscle inflammation leads to muscle weakness

• Untreated muscle disease leads to permanent disability

• There are other causes of weakness and diagnosis has to be made with consideration of conditions that can be Myositis " mimics".

• Treatment involves specialized immunosuppressive therapy.