DM is believed to result from an immune system process triggered by outside factors such as cancer, drugs, or infections in genetically predisposed individuals. After being exposed to the triggering agent, the body’s immune system mistakenly attacks its own cells in addition to the original trigger. We know that genetics play an important role in developing DM because of identical twin studies -- when one twin develops DM, the other frequently does as well.

The most important feature in diagnosing DM is the skin finding called poikiloderma. Poikiloderma is a fancy word for areas of the skin that are made up of darker pigment, lighter pigment, and tiny blood vessels that together result in a pink/violet appearance. Poikiloderma is typically present along sun exposed areas such as the “V” of the chest and upper back. This is commonly referred to as the “shawl sign”. Nail cuticles can often look ragged with the appearance of tiny blood vessels.

DM lesions are also distributed around the eyes (the heliotrope sign), knuckles and elbows; however these findings may be subtle. There can also be assoicated swelling around the eyes and face. When lesions are present on the knuckles they are referred to as Gottron’s papules. When present on the elbows, this is known as Gottron’s sign. These skin lesions may itch which can significantly affect patients’ quality of life. Dermatologists will often look for signs of other autoimmune diseases such as rheumatoid arthritis, scleroderma, or lupus because symptoms can sometimes overlap. Some patients initially present with skin findings with no muscle disease. When following these patients long term, some will never develop muscle weakness (amyopathic dermatomyositis) while others eventually develop full-blown dermatomyositis (with muscle disease).

Shawl Sign

Nail Changes

Heliotrope Sign

Gottron’s Papules

Systemic Disease

Patients with DM usually present with complaints of malaise and loss of energy. Skin findings often come before muscle disease begins. Muscle weakness begins in proximal muscle groups (such as the triceps and quadriceps) in a symmetric fashion. Patients may have difficulty completing simple tasks such as combing hair or rising from a sitting position. Muscles are often sore to the touch.

Calcinosis is a common finding in patients with juvenile DM. Lesions may be hard, irregular nodules under the skin or within muscle tissue. Calcinosis favors sites of trauma such as elbows, knees, and fingers, but may occur anywhere. Lesions may be painful.

Pulmonary (lung) disease occurs in 15-30% of patients with DM. There may be associations with heart disease and diabetes.

Cancer

Roughly 10-50% of patients with DM will eventually develop some form of cancer including ovarian, colon, nose/throat, breast, lung, stomach, pancreas, and lymphoma. The best approach to managing this increased risk to be vigilant to any new symptoms and to frequently see your physician.

Patients who present with characteristic skin findings should undergo a skin biopsy to confirm the clinical diagnosis. Following diagnosis, your physician will monitor for muscle weakness and other systemic disease. Evaluation for myositis can include: strength testing of proximal extensor muscles (triceps, quadriceps), muscle enzyme levels, electromyograms, and a muscle biopsy. Increasingly MRI and ultrasound of proximal muscles can be used in lieu of a muscle biopsy.

Patients with normal muscle enzyme levels should still be followed at regular interval as the disease may progress. Your physician may also evaluate you for other systemic disease (heart, lungs, and esophagus). Patients should visit their physician every 4-6 months and be screened for cancer annually for at least 2-3 years.

As with many rare skin disease, there are few double-blind, placebo-controlled trials evaluating various treatment options. There have been a series of individual case reports which suggest 75-85% of patients can become muscle disease-free, off treatment after a period of 24-48 months, utilizing a slow corticosteroid (prednisone) taper. Physical therapy and exercise have shown to improve muscle strength and endurance. Exercise does not trigger myositis flares. Your dermatologist may consider treatments such as methotrexate, azathioprine, IVIg, among other immune system modulators. Available therapy for skin disease is similar (and also includes topical corticosteroids), however, it may be inadequate with many patients continuing to report skin findings and itch. Patients with skin disease without muscle weakness are typically not treated with systemic corticosteroids. Patients with calcinosis cutis may respond to the calcium channel blocker diltiazem.

Corticosteroids such as prednisone carry a risk of some side effects. Patients are at an increased risk for osteoporosis which should be monitored routinely by a physician. Patients should have their blood pressure and glucose levels routinely monitored as there may be an increased risk of high blood pressure and diabetes.