Myositis is the general term given to chronic and progressive inflammation of the muscles. The condition is often characterized by weakness, muscle pain, fatigue, difficulty breathing, trouble swallowing, and swelling. 

Myositis is a rare disease that can be difficult to diagnose, and the cause is sometimes unknown. Symptoms of the condition can appear without warning or gradually over time.

Some types of myositis are associated with rashes, and the disease can affect both children and adults. All but one type of myositis is more prevalent in women than men. 

Types of Myositis


Amongst all types of myositis, dermatomyositis (DM) is the easiest to diagnose. It is characterized by purple-red rashes shaped like a heliotrope flower.

The rash forms on the eyelids, face, chest, neck, and back. The joints, including the knuckles, elbows, knees, and toes, are not exempted. Muscle weakness typically follows.

Other symptoms of dermatomyositis include:

  • Scaly, dry, or rough skin
  • Trouble rising from a seated position
  • Bumps all over the knuckles, elbows, and knees, also known as Gottron’s papules or Gottron’s sign
  • Weakness in the neck, back, hip and shoulder muscles
  • Fatigue
  • Hoarseness in the voice
  • Difficulty swallowing
  • Muscle pain
  • Hardened lumps of calcium under the skin
  • Joint inflammation
  • Irregular heartbeat
  • Weight loss
  • Gastrointestinal ulcers

Juvenile myositis

Juvenile myositis (JM) typically occurs in children under 18. Girls are twice as likely to develop the disease as boys. Like other forms of myositis, JM is characterized by skin rashes and muscle weakness. 

Symptoms of JM include:

  • A visible, reddish-purple rash over the eyelids or joints
  • Moodiness or irritability
  • Fatigue
  • Difficulties in motor function, such as standing from a seated position, trouble climbing stairs, and getting dressed
  • Stomach aches
  • Difficulty reaching overhead
  • Swelling of the skin around the fingernails
  • Difficulty lifting the head
  • Difficulty swallowing
  • Muscle weakness
  • Hardened lumps of calcium under the skin
  • Fever
  • Hoarse-sounding voice
  • Muscle and joint pain
  • Gottron’s papules 

Inclusion-body Myositis

Inclusion-body myositis (IBM) is the only type of myositis that is more prevalent in men than in women. It is a condition that affects those aged 50 and above.

IBM typically begins with muscle weakness in the wrists and fingers and also in the thigh muscles. The muscle weakness is more pronounced in smaller muscles and is asymmetrical, with one side of the body affected more than the other.

The disease is believed to be genetic.

Symptoms of inclusion-body myositis include:

  • Difficulty walking
  • Frequent falls
  • Tripping and loss of balance
  • Weakened hand grip and diminished dexterity of hands and fingers
  • Trouble rising from a seated position
  • Muscle weakness
  • Difficulty swallowing
  • Impaired deep tendon reflexes
  • Muscle pain

Toxic myositis

Toxic myositis is thought to occur as a result of certain prescribed medications and illicit drugs. Medications that lower cholesterol, such as statins, may be among the most common drugs to cause this condition.

Although this is extremely rare, other drugs and substances that may cause myositis include:

  • Certain immunosuppressants
  • Cocaine
  • Adalimumab (Humira)
  • Omeprazole (Prilosec)
  • Toluene, a solvent used in paint thinners

Symptoms of toxic myositis are seem like those of other types of myositis. People who experience this disease typically see improvement once they stop the medication that caused the toxicity.


Polymyositis (PM) starts with weakness in the muscles closest to the trunk of the body and then spreads from there. Each case of this condition is unique, and people with polymyositis often have comorbid autoimmune diseases. 

Symptoms of polymyositis include:

  • Muscle weakness
  • Difficulty swallowing
  • Muscle pain
  • Trouble rising from a seated position
  • Falling
  • Chronic dry cough
  • Fatigue
  • Difficulty breathing
  • Thickening of the skin on the hands
  • Weight loss
  • Fever
  • Hoarse voice

Causes of Myositis

Inflammatory conditions: Diseases that cause inflammation all over the body may affect the muscles, causing myositis. Autoimmune disorders – in which the body attacks its own tissues – are chiefly responsible for myositis.

Inflammatory conditions capable of causing myositis include:

  • Polymyositis
  • Dermatomyositis
  • Inclusion body myositis

Inflammatory conditions are often the most severe cause of myositis, requiring long-term treatment.

Infection: Viral infections are the most common infections that cause myositis. In rare cases, fungi, bacteria, or other organisms can cause myositis as well. These microorganisms may invade muscle tissue directly or release substances that damage muscle fibers. Common cold and flu viruses and HIV are some of the viruses that can cause myositis.

Injury: Vigorous exercise can result in muscle pain, swelling, and weakness for a while after a workout. Inflammation contributes to these symptoms, making this a form of myositis. Myositis symptoms that occur after exercise or injury nearly always resolve entirely with rest and recovery.

Drugs: Some medications and drugs can cause temporary muscle damage. Since inflammation in the muscles is not usually identified, the muscle problem may be described as myopathy rather than myositis.

Drugs causing myositis or myopathy include:

  • Statins
  • Alpha-interferon
  • Plaquenil (hydroxychloroquine)
  • Colchicine
  • Alcohol
  • Cocaine

Myopathy may occur immediately after starting a drug or may occur after taking medication for months or years. It is sometimes caused by an interaction between two different medications. Severe myositis from medications is rare.

Rhabdomyolysis: This is a condition that occurs when muscles break down quickly. Rhabdomyolysis is characterized by muscle pain, weakness, and swelling. Urine may also turn a red or dark-brown color. 


The following tests can be used to confirm myositis in a patient:

Blood tests: The presence of high levels of muscle enzymes, such as creatine kinase, may indicate muscle inflammation. Other blood tests check for abnormal antibodies that may identify an autoimmune disorder.

  • MRI scan: This procedure involves using a scanner with a high-powered magnet and a computer to create images of the muscles. An MRI scan can help identify areas where myositis occurs and changes in the muscles over time.
  • Electromyography (EMG): A doctor can test muscles’ response to electrical nerve signals by inserting needle electrodes into muscles. EMG can identify muscles that are weak or damaged by myositis.
  • Muscle biopsy: This is the most accurate test for diagnosing myositis. A doctor identifies a weak muscle by making a small incision and removing a small muscle tissue sample for testing. Muscle biopsy results in a final diagnosis in most people with myositis.


Myositis treatments vary depending on the cause of the condition.

Myositis caused by inflammatory conditions may require treatment with medications that suppress the immune system. These include:

  • Methotrexate
  • Prednisone
  • Azathioprine

Myositis caused by viral infections has no specific treatment. Cases of bacteria-causing myositis are rare and usually require antibiotics to prevent the spread of the disease. 

Drug-related myositis is treated by stopping the medication. Muscle inflammation typically subsides within a few weeks after stopping the medication.