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Diagnosing Dermatomyositis

Specialists at NYU Langone have the experience and resources to diagnose dermatomyositis, a rare inflammatory condition characterized by a skin rash and chronic muscle weakness. These symptoms are the result of inflammation, which occurs when the body’s immune system is activated.

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Usually, inflammation is a temporary response to a foreign substance, such as a virus, and disappears after the immune system has destroyed it. But in people who have dermatomyositis, inflammation persists. Over time, it damages skin cells and muscle fibers. Because the condition causes muscle weakness, it is considered a type of inflammatory myopathy, a muscle disease related to inflammation.

Dermatomyositis may enter remission, or a period of inactivity, after about five years, but often, the condition remains chronic. There is no cure, and most people require some form of treatment, such as medication or physical therapy, to manage symptoms.

Children who have dermatomyositis are treated at Hassenfeld Children’s Hospital at NYU Langone.

Symptoms and Causes

The rash associated with dermatomyositis may appear in patches, is usually purple or red, and often appears on sun-exposed areas of the body such as the upper chest, face, upper back, eyelids, knuckles, and scalp. It can, however, affect skin on any part of the body. The rash may be intensely itchy, and exposure to sunlight may worsen symptoms.

Most, but not all, people with dermatomyositis also experience symmetrical muscle weakness on both sides of the body. The condition usually affects muscles in the thighs, upper arms, neck, and shoulders. A common sign is difficulty raising the arms. Brushing your teeth or hair may also be difficult. Muscle weakness in the hips and thighs may affect your ability to get up from a chair without assistance.

In children with dermatomyositis, calcium deposits can occur at the sites of inflammation, and may further restrict movement.

Dermatomyositis may also cause weakness in the esophagus—the muscular tube that connects the mouth to the stomach—and can lead to difficulty swallowing. In rare instances, the condition may affect the muscles of the heart; this often occurs without any symptoms. In addition, the condition may lead to lung inflammation, at times causing shortness of breath.

The cause of the inflammatory response associated with dermatomyositis is unknown. The condition affects more women than men. In some people, skin and muscle symptoms develop suddenly. In others, they may begin as a red or purple rash on the face or hands, which slowly spreads to other areas of the body over several weeks. The rash is usually accompanied by decreasing strength in the upper arms and thighs, but the rash may occur months or years before these symptoms develop.

A person may develop a rash without any muscle weakness. This is called amyopathic dermatomyositis, and it occurs in about 20 to 25 percent of people with this condition. In others, muscle involvement is the primary feature, and only a subtle rash is present.

Dermatomyositis is associated with cancer in about 25 percent of adults who have the condition. As a result, our doctors recommend a variety of screening tests to diagnose any cancers early. Dermatomyositis is not generally associated with cancer in children.

Tests to evaluate any lung, esophageal, or cardiac problems are also part of the diagnostic process.

Diagnostic Tests

Doctors can often identify the signs and symptoms of dermatomyositis during a medical history and physical exam. Our dermatologists, neuromuscular experts, and rheumatologists—doctors who specialize in inflammatory conditions in muscles and joints—work together to determine the diagnosis.

Medical History and Physical Exam

Early diagnosis of dermatomyositis is important because it allows doctors to start treatment before the condition progresses. To diagnose the condition, a doctor asks about your health, including when you first noticed symptoms, how frequently they occur, whether you have trouble swallowing or breathing, and whether you are able to perform everyday tasks, such as brushing your teeth or getting up from a chair.

Your doctor examines your skin for signs of inflammation, such as redness, swelling, and a rash.

Your doctor may also ask you to move or walk in different ways to assess whether you’ve lost muscle function and whether any weakness occurs on both sides of your body.

Blood Tests

A technician takes a small sample of blood, then sends it to a laboratory to test it for substances associated with dermatomyositis that may indicate muscle damage or inflammation. Doctors also use blood tests to rule out other medical conditions that cause a rash and muscle weakness, such as systemic lupus erythematosus.

Test results are generally available in several days. If necessary, more advanced testing may be done, and can take several weeks to get results.

Skin and Muscle Biopsies

To confirm a diagnosis of dermatomyositis, our doctors may perform a punch biopsy, in which a dermatologist uses a device that resembles a pencil to puncture the skin and remove a small tissue sample. The incision is closed with one or two stitches. This test takes about five minutes and can be done in the doctor’s office.

In some instances, a muscle biopsy may be recommended. To perform this test, a rheumatologist or neuromuscular specialist injects a local anesthetic to numb the skin, then inserts a needle into the muscle to remove a small tissue sample.

The doctor sends each of these samples to a laboratory for testing. Most of the time, the results are available in about two weeks.


An electromyogram (EMG) can reveal whether dermatomyositis has caused muscles to become less responsive to nerve impulses, which normally trigger muscle movement. The test measures electrical impulses transmitted along nerves, nerve roots, and muscle tissue.

During this test, a doctor inserts small, thin needles, called electrodes, through the skin and into muscles that correspond to specific nerves. Your doctor asks you to move these muscles one at a time. The signals that are recorded help doctors determine the extent of weakness in the muscles.

An EMG is relatively painless. It usually takes about 15 to 30 minutes to complete.

MRI Scans

An MRI scan uses a magnetic field and radio waves to create computerized, three-dimensional images of structures inside the body. MRI images allow doctors to examine the muscles from a variety of angles. Your doctor may use an MRI scan to assess the extent of inflammation in muscle groups throughout your body.

Screening Tests

After a doctor has confirmed that you have dermatomyositis, he or she almost always recommends further testing to screen for medical conditions commonly associated with dermatomyositis. These include lung disease, cardiovascular disease, esophageal involvement, and, in adults, cancer.

Many people who are diagnosed with dermatomyositis do not develop these conditions, but our doctors recommend screening to ensure that you receive immediate treatment if needed.


An electrocardiogram, or EKG, is a tool cardiologists use to record electrical activity in the heart. In rare instances, dermatomyositis may cause an irregular heartbeat, which is called an arrhythmia. To perform an EKG, a doctor attaches several small electrodes to the skin in different parts of your body. Electrodes transmit the rhythm of your heartbeat to a machine so your doctor can analyze it.

Pulmonary Function

Pulmonary function tests measure how much and how quickly air is inhaled and exhaled. During this test, a pulmonologist, who treats lung conditions, asks you to breathe through an air mask while a machine called a spirometer records information about your breathing. You may be asked to breathe deeply or take short rapid breaths so your doctor can evaluate lung function under different circumstances.

As part of pulmonary function testing, your doctor performs a diffusion capacity test, which measures how well the lungs move gases—such as oxygen and carbon dioxide—into and out of the bloodstream. During this test, a doctor asks you to inhale a small amount of a gas, such as carbon dioxide, and then quickly exhale. This enables your doctor to determine how much of the gas the lungs absorbed during inhalation.

Esophageal Motility

An esophageal motility test assesses how well the muscles are working in the esophagus, the tube that carries food and liquids from the mouth to the stomach. Some people with dermatomyositis may experience weakness in the esophageal muscles, making swallowing difficult.

During this exam, a doctor inserts a long, thin instrument called a catheter through the nose and into the esophagus and stomach. While it is in place, you are asked to swallow small sips of water so sensors can record the pressure, strength, and pattern of muscle contractions in the esophagus.

Cancer Screening

Chronic inflammation can cause changes in the body’s cells, putting adults with dermatomyositis at risk for cancer in the first three to five years after diagnosis. After this period of time, the risk of cancer drops to what it would be if dermatomyositis had never been diagnosed, even if you still have the condition. NYU Langone doctors recommend screening tests so that cancer can be detected as early as possible.

In women, doctors recommend imaging tests of the pelvis to determine if ovarian cancer is present, as well as a mammogram, an X-ray of a woman’s breasts, which is used to check for breast cancer. In men, doctors recommend a prostate exam. Doctors may also recommend a colonoscopy, an imaging test of the large intestine that can reveal colon cancer.

Other tests include a chest X-ray or CT scan—which uses X-rays and a computer to create three-dimensional images of the body—to screen for lung cancer. Your doctor may also recommend blood tests to determine your risk of thyroid cancer, which affects the thyroid, a gland that regulates certain hormones related to the body’s metabolism.

Our Research and Education in Dermatomyositis

Learn more about our research and professional education opportunities.