Dermatomyositis is one of the autoimmune connective tissue diseases. The name is derived from dermato=skin, myo=muscle, and itis=inflammation. Thus, inflammation of unknown cause leads to a distinctive skin rash and weakness and tenderness of the muscles, particularly of the hip and shoulder girdles. Dermatomyositis (DM) affects women more than men (about 2 to 1), usually between the ages of 40 and 60 years, but there is also a childhood form of DM.
Most patients with DM are photosensitive, and from the point of view of a dermatologist, often note the onset of the rash after a prolonged or exaggerated sun exposure. As I will discuss, although some of the skin features of DM are diagnostic by recognition, they may not always be present, and the muscle weakness may not appear until months later. The picture is further complicated by the possible association or overlap of DM with scleroderma, lupus, and rheumatoid arthritis.
When all the pieces of the puzzle fit together, DM is a dermatologist’s dream because DM has a host of special “signs” attributed to it that aid in differentiating it from lupus, lichen planus, and psoriasis.
Heliotrope sign: named after the flower, refers to violet discoloration and subtle swelling of the upper eyelids or the entire peri-orbital skin.
Gottron’s papules: reddish violet bumps or plaques overlying the knuckles and
possibly the elbows and knees.
- Shawl sign: sun-damage of the upper back and chest showing thinning of the skin, decreased and increased pigment, and dilated blood vessels. Together, these skin changes are called poikiloderma.
Holster sign: poikiloderma on the sides of the thighs.
Enlarged, dry cuticles and dilated capillaries around the fingernails.
- Redness, scaling, and itching of the scalp may be easily confused with psoriasis.
Laboratory tests performed to clarify the diagnosis may actually confuse the picture. Here’s why: most clinicians will be considering lupus because of the photosensitivity and the presence of “rashes.” The anti-nuclear antibody blood test is positive in 2/3 cases of DM which can mislead. A skin biopsy generally shows an “interface dermatitis” which indicates a connective tissue disease but is not specific for either lupus or DM. Direct immunofluorescence testing of the skin biopsy specimen will be negative in DM or show non-specific results which can also be seen in lupus. However, even if there is no muscle weakness demonstrated, the muscle enzymes in the blood may be elevated, an indication of inflammation producing muscle damage. Skin manifestations may precede muscle disease in 50% of cases, but myositis can eventually be detected during the following 6 months using tests such as MRI, electromyogram, and muscle biopsy.
Thus, photosensitivity, the presence of some of the listed skin signs (especially #1 and 2), and elevated blood levels of creatine kinase and/or aldolase can clinch the diagnosis of DM.
Treatment of Dermatomyositis
There is a partial disconnect between the treatment of the skin and muscle inflammation in DM. The myositis usually responds to high dose systemic prednisone, but rashes are often resistant. Plaquenil or hydroxychloroquine improves about 80% of DM patients with skin signs but does not help myositis. Skin treatment must also include sun avoidance and sunscreen use; topical creams such as corticosteroids, tacrolimus, and pimecrolimus may improve the rashes. Then there are some drugs that can help both skin and muscle manifestations. These are intravenous immunoglobulin (IVIG), methotrexate, mycophenolate mofetil, cyclosporine, and rituximab. A paper in the Journal of the American Academy of Dermatology (October 2013) reported on the successful treatment of 13 DM patients with resistant skin disease. All 13 patients improved, and 8 cleared completely with IVIG at a dose of 2 grams per kilogram infused every 4 weeks. In all cases, the dosages of prednisone or other immunosuppressive drugs could be reduced or discontinued thereby lowering the risk of side-effects.
Association with Cancer
It has been established that patients with DM have a higher than expected incidence of internal cancer within the first 3 years of the DM diagnosis. Cancer develops in 15-30% of patients during this time period. The types of cancers reported are quite variable and may include uterine, ovarian, lung, pancreatic, colon, and lymphoma. Screening for internal malignancy is recommended at the diagnosis of DM and annually for 3 years utilizing body CT scans, mammogram, PAP smear, chest X-ray, colonoscopy, and other age- and gender-appropriate tests. If the rash improves or clears after the cancer is discovered and treated, a later flare-up of DM requires a search for recurrence or spread of the cancer.
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