Dermatomyositis

Signs and symptoms

The main symptoms include several kinds of skin rash along with muscle weakness in both upper arms or thighs.

One form the rashes take is called "heliotrope" (a purplish color) or lilac, but may also be red. It can occur around the eyes along with swelling, but also occurs on the upper chest or back what is called the "shawl" (around the neck) or "V-sign" above the breasts and may also occur on the face, upper arms, thighs, or hands. Another form the rash takes is called Gottron's sign which are red, sometimes scaly, papules that erupt on any of the finger joints (the metacarpophalangeal joints or the interphalangeal joints). All these rashes are made worse by exposure to sunlight, and are often very itchy, painful, and may bleed.

Around 30% of people have swollen, painful joints, but this is generally mild.

In some people the condition affects the lungs, and they may have a cough or difficulty breathing. If the condition affects the heart, there may be arrhythmias. If it affects the blood vessels in the stomach or intestines, which is more common in juvenile DM, the person might vomit blood, have black, tarry bowel movements, or may develop a hole somewhere in their GI tract.

Causes

The cause is unknown, but it may result from an initial viral infection or cancer, either of which could raise an autoimmune response.

Between 7 and 30% of dermatomyositis arise from cancer, probably as an autoimmune response. The most common associated cancers are ovarian cancer, breast cancer, and lung cancer. 18 to 25% of people with amyopathic DM also have cancer.

Some cases are inherited, and HLA subtypes HLA-DR3, HLA-DR52, and HLA-DR6 seem to create a disposition to dermatomyositis.

Diagnosis

The diagnosis of dermatomyositis is based on five criteria which are also used to differentially diagnose with respect to polymyositis:

1. Muscle weakness in both thighs or both upper arms
2. Using a blood test, finding higher levels of enzymes found in skeletal muscle, including creatinine kinase, aldolase, as well as glutamate oxaloacetate, pyruvate transaminases and lactate dehydrogenase
3. Using testing of electric signalling in muscles, finding all three of the following: erratic, repetitive high frequency signals; short, low energy signals between skeletal muscles and motor neurons that have multiple phases; and sharp activity when a needle is inserted into the muscle
4. Examining a muscle biopsy under a microscope and finding mononuclear white blood cells between the muscle cells, and finding abnormal muscle cell degeneration and regeneration, dying muscle cells, and muscle cells being consumed by other cells (phagocytosis)
5. Rashes typical of dermatomyositis, which include heliotrope rash, Gottron sign and Gottron papules

The fifth criterion is what differentiates dermatomyositis from polymyositis; the diagnosis is considered definite for dermatomyositis if three of items 1 through 4 are present in addition to 5, probable with any two in addition to 5, and possible if just one is present in addition to 5.

Dermatomyositis is associated with autoantibodies, especially antinuclear antibodies (ANA). Around 80% of people with DM test positive for ANA and around 30% of people have myositis-specific autoantibodies which include antibodies to aminoacyl-tRNA synthetases (anti-synthetase antibodies), including antibodies against Histidine—tRNA ligase (also called Jo-1); antibodies to signal recognition particle (SRP); and anti-Mi-2 antibodies.

Magnetic resonance imaging may be useful to guide muscle biopsy and to investigate involvement of internal organs; X-ray may be used to investigate joint involvement and calcifications.

A given case of dermatomyositis may be classified as amyopathic dermatomyositis if only skin is affected and there is no muscle weakness for longer than 6 months according to one 2016 review, or two years according to another.

Classification

Dermatomyositis is a form of systemic connective tissue disorder, a class of diseases that often involve autoimmune dysfunction.

It has also been classified as an Idiopathic inflammatory myopathy along with polymyositis, necrotizing autoimmune myositis, cancer-associated myositis, and sporadic inclusion body myositis.

There is a form of this disorder that strikes children, known as juvenile dermatomyositis (JDM).

Treatment

There is no cure for dermatomyositis, but the symptoms can be treated. Options include medication, physical therapy, exercise, heat therapy (including microwave and ultrasound), orthotics and assistive devices, and rest. The standard treatment for dermatomyositis is a corticosteroid drug, given either in pill form or intravenously. Immunosuppressant drugs, such as azathioprine and methotrexate, may reduce inflammation in people who do not respond well to prednisone. Periodic treatment using intravenous immunoglobulin can also improve recovery. Other immunosuppressive agents used to treat the inflammation associated with dermatomyositis include cyclosporine A, cyclophosphamide, and tacrolimus. Physical therapy is usually recommended to prevent muscle atrophy and to regain muscle strength and range of motion. Many individuals with dermatomyositis may need a topical ointment, such as topical corticosteroids, for their skin disorder. They should wear a high-protection sunscreen and protective clothing. Surgery may be required to remove calcium deposits that cause nerve pain and recurrent infections.

Antimalarial medications, especially hydroxychloroquine and chloroquine, are used to treat the rashes, as they are in similar conditions.

Rituximab is used when people don't respond to other treatments.

As of 2016, treatments for amyopathic dermatomyositis in adults did not have a strong evidence base; published treatments included antimalarial medications, steroids, taken or orally or applied to the skin, calcineurin inhibitors applied to the skin, dapsone, Intravenous immunoglobulin (IVIG), methotrexate, azathioprine, and mycophenolate mofetil. None appear to be very effective but among them, IVIG has had the best outcomes.

Prognosis

Before the advent of modern treatments such as prednisone, intravenous immunoglobulin, plasmapheresis, chemotherapies, and other drugs, the prognosis was poor.

The cutaneous manifestations of dermatomyositis may or may not improve with therapy in parallel with the improvement of the myositis. In some patients the weakness and rash resolve together. In others, the two are not linked, with one or the other being more challenging to control. Often, cutaneous disease persists after adequate control of the muscle disease.

The risk of death from the condition is much higher if the heart or lungs are affected.

Epidemiology

Around ten people in a million have DM, and around 2 people in a million have the amyopathic DM. DM is twice as common in women as in men.

History

The diagnostic criteria were proposed in 1975 and became widely adopted. Amyopathic DM, also called DM sine myositis, was named in 2002.

Society and culture

Research

As of 2016, research was ongoing into causes for DM, as well as biomarkers; clinical trials were ongoing for use of the following drugs in DM: ajulemic acid (Phase II), adrenocorticotropic hormone gel (Phase IV, open label), IMO-8400, an antagonist of Toll-like receptor 7,8 and 9 (Ph II), abatacept (Phase IV, open label), and sodium thiosulfate (Phase II).