Inflammatory myopathies

Symptoms

The most common presentation of these illnesses is muscular weakness, which usually has a characteristic effect on the proximal skeletal muscles, that is to say, on the shoulder and hip girdles, which makes activities needing these muscles to work normally difficult, such as hanging out laundry, combing hair, going up stairs or getting up from a chair. Skin manifestations are characteristic in dermatomyositis and we can identify a wide range of lesions. The majority of them have a certain photosensitivity component which means they usually appear in areas exposed to the sun. Lilac-coloured or heliotrope palpebral oedema are considered to be pathognomic, as are Gottron's papules, which appear on the knuckles of the hands. Similar lesions can be seen in the extension areas, such as elbows and knees, and also on the hair line on the scalp and nape of the neck. Other cutaneous lesions, which are V-shaped on the neckline or shawl-shaped on the back, are also related to the stimulation of the sun.

The most well-known respiratory infection in patients with dermatomyositis and polymyositis is interstitial lung disease. In general, its inception is usually sub-acute or chronic and the clinical findings during the examination can detect dry, crackling rales, in “velcro”, which are characteristic of pulmonary fibrosis.  Cardiac and digestive involvement is infrequent and should be assessed in each patient individually.

Who is affected by the condition?

Inflammatory myopathies can be considered to be within the rare disease group due to their low incidence. Epidemiological studies carried out around the world set out an average annual incidence of 2.1 to 7.7 new cases for every million inhabitants per year.

It is considered to be a universally distributed disease, although it is a little more prevalent in Caucasians and less frequent in black people. It is twice as frequent in women than men. In addition, although a juvenile form exists that usually appears before the age of 16, signs of the illness are more frequent in 30 to 40 year olds.

Diagnosis

The diagnosis is made using the convergence of clinical criteria. The most relevant finding in blood tests is elevated muscular enzymes, such as creatine kinase and aldolase, along with acute phase reactors such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Muscular biopsy is, for some authors, the benchmark test for diagnosing inflammatory myopathies.

In the case of dermatomyositis and, in general, inflammatory myopathies, there are a series of antibodies that help the clinician to classify the disease. Anti-Jo-1, anti-PL-7, anti-PL-12, anti-U1 and anti-PM-Scl, etc, stand out amongst these antibodies. Another complementary test enabling assessment of the extent of the adverse effect on muscles is the nuclear magnetic resonance which, in turn, is valuable when monitoring progress. Depending on whether there is pulmonary, cardiac or digestive involvement, the extra examinations needed to assess each affected organ will be carried out.

Standard treatment

Treatment of inflammatory myopathies is based on administering glucocorticoids and immunosuppressants, without forgetting physical therapy or rehabilitation, even in the acute phase. A third of patients respond to a single glucocorticoid treatment, but the majority need the addition of a new immunosuppressant, such as disease modifying drugs, including methotrexate, ciclosporin, cyclophosphamide, azathioprine, mofetil mycophenolate and tacrolimus. Intravenous immunoglobulins may also be used as they act to improve muscle weakness. Biological therapies, such as etanercept, infliximab and rituximab, have been shown to be effective in some clinical cases or observational studies. In any event, the treatment must be individual for each patient.