Definition

Dermatomyositis is part of Myositis (muscle inflammation) diseases. There are several types which are described in more detail on the page Myositis. The symptoms overlap, but dermatomyositis is characterized by a rash in addition to rheumatic inflammation of the muscles. Dermatomyositis (juvenile dermatomyositis) is discussed on its own page.

Disease Causes

In most cases, the cause of dermatomyositis is unknown. Dermatomyositis in adults is associated with breech presentation cancer in some cases. When the disease has first started, we know that the body's own immune system mistakenly attacks muscles and skin (Autoimmune disease). Internal organs, especially the lungs and the heart, can also be damaged. In severe muscle inflammation, the kidneys can also fail.

Occurrence

Myositis diseases are rare with 1-8 cases per 100.000 population (prevalence). Dermatomyocyte and Polymyocyte occur about as frequently (reference: Dobloug C, 2015). The number of new people who get the disease per year (incidence) is estimated at 0,5-8 per million, which corresponds to approx. 25 new cases in Norway annually. Dermatomyositis is thus defined as a rare disease. Women are attacked twice as often as men. Most people become ill at the age of 50, but also children (most often Juvenile dermatomyositis) and elderly people can be attacked.

Symptoms

The skin

Gottrons` sign. The skin may have red-purple color changes over the knuckles of the fingers, the stretching side (extensor) of the elbows and knees (Gottron's sign / papels). People of color develop pigmented, dark, skin changes.

V sign and shawl sign. Some also get skin changes on the neck and neck areas (V- sign or shawl- sign).

Heliotropic rash. Red-purple or dark areas on and around the upper eyelid are called Heliotropic rash.

Mechanic hands. Cracked and chipped skin on fingers is often referred to as "mechanic hands”. These are typically seen at Antisynthetase syndrome where the lungs are always also attacked.

Calcinosis. Calcium deposits (calcinosis) under the skin occur especially in children with (juvenile) dermatomyositis. Other reasons for calcinosis is described in a separate chapter.

Sores and knots on fingers and in fatty tissue combined with lung symptoms may be due to the anti-MDA 5 syndrome described below.

Illustration above: Dermatomyositis with a red face and swollen eyelids. Illustration: By Elizabeth M https://commons.wikimedia.org.  CC BY SA 3.0

Illustration: V signs are redness of the throat and chest at Dermatomyositis. Openi. Affiliation: Department of General Surgery, Changi General Hospital, Singapore. CC BY 4.0

Muscles

Myositis symptoms with gradual weakening develop gradually over weeks and months occur in some cases. Less than half experience that the muscles are painful. Gradually weakened muscle strength in the thighs can manifest itself in the fact that it becomes increasingly difficult to get up from a squatting position or from a chair. Weak upper arms make it difficult to lift the arms above the head. In some people, the neck muscles become weak so that the head feels heavy to hold.

Lungs

Dermatomyositis can attack the lungs. Some people first get lung symptoms with noticeable heavy breathing during physical exertion and skin/muscle symptoms afterwards. Antisynthetase syndrome diagnosed with lung changes (detected by CT examinations and lung function measurements) And when antibodies Yes-1, Pl-7, Pl-12 (rarely Ha, Zo, EJ, KS and OJ antibodies) are detected. MDA-5 syndrome with typical skin changes, nodules in the palms, joint inflammation and MDA-5 antibody are described in more detail below. More about lung disease in rheumatic diseases here.

Anti MDA5 Myositis Syndrome

Definition. MDA5 myositis syndrome is a form of Dermatomyositis, but the inflammation of the muscles is not very pronounced ("amyopathic dermatomyositis"). However, the lung symptoms are often severe. Everybody has antibody MDA5 although ANA is usually negative / non-existent.

Symptoms. Rapidly increasing lung manifestation (and breathing difficulties), ulcerations (wounds) and panniculitis, adipose tissue inflammation) in the skin, swollen hands often with sores, nodules in the palms- Arthritis (arthritis), sSound in the mouth, alopecia (hair loss).

Blood tests; anti-MDA5 antibody (often required specially) Antinuclear Antibodies (ANA) and antisynthetase antibody is often absent. Creatine kinase / CK is only slightly elevated or normal. MDA-5 antibody is analyzed, among other things, at the OUS, Immunological laboratory.

Diagnosis is based on typical lung changesMDA5 antibody and the absence of other explanations

Similar conditions, differential diagnoses: Infection with various bacteria or pneumocystis jiroveci, Antisynthetase syndrome, other systemic connective tissue disease with pulmonary manifestation, Systemic sclerosis, Scleromyositis and, Dermatomyositis, rheumatoid arthritis (Arthritis) with pulmonary manifestations, IPAF (Interstitial pneumonia with autoimmune fertures), Idiopathic pulmonary fibrosis.

Treatment; Corticosteroids in high doses combined with disease suppressants DMARDs for example mycophenolate, tacrolimus or cyclophosphamide.

Prognosis: Survival is individual and dependent on prompt treatment, survival 60-70%.

References: Hall JC, 2013, Hi S, 2018

Investigations in dermatomyositis

Medical history includes current symptoms from, among other things, skin, muscles and lungs (see above). Symptoms of cancer in adults with dermatomyositis should also be investigated because a connection exists in some cases.

Clinical the skin is examined, especially on the fingers, face, neck and above the neck. Muscle strength can be tested by whether one can get up from a chair or squat without support and whether arms can be lifted without problems against gravity.

Blood tests shows elevated CK (Creatinin Kinase), often the "liver enzymes" AST and LD are also elevated. Typical Antibodies examined, possibly by "myositis bolt" which are myositis-specific special tests.

Imaging may include MRI of muscles (most often thigh muscles) which in myositis show signs of inflammation on both sides. CT of the lungs is appropriate if pulmonary manifestations are suspected.

Other. EMG (Electromyography) can show muscle inflammation and can distinguish myositis from neurogenic muscle diseases

Tissue sample (biopsy) from muscles will show a typical inflammatory infiltrate in dermatomyositis round blood vessels in muscles peri-fascicular rheumatic (autoimmune") and not in the endomysia / muscle cell itself, unlike Polymyocyte which has endo-myseal inflammation. A tissue sample from the skin may show inflammatory changes (inflammation) suspicious of systemic connective tissue disease, but is not decisive/specific for the diagnosis.

Cancer and Dermatomyositis

Dermatomyositis in adults may be associated with cancer. It is therefore common to examine for this (CT chest and abdomen, mammography, stool samples, if necessary PET / CT and follow-up). Generally more about cancer and rheumatic disease in a separate chapter.

Similar conditions, differential diagnosis in myositis and dermatomyositis

There are many diseases similar to myositis and should be considered in the medical investigation. Also, when treatment does not work as expected, similar conditions should be carefully considered.

• ALS (amyotrophic lateral injury): Distal affection, hyper-reflexia, muscle fibrillation, spasms, slightly increased CK
• Amyloid myopathy: Changes deeper under the skin. Proteins in the urine. Typical tissue sample when stained with Congo red
• Carnitine palmitoyl transferase II deficiency: Muscle pain
• Diabetic amyotrophy and diabetic muscle infarction in diabetes Type 2: Acute, asymmetric onset with focal pain and weakness in thighs. Often weight loss. EMG differentiates from myositis
• Electrolyte deficiency: hypo-kalaemia, hypo-calcaemia, hypo-magnesaemia
• Eosinophilic myositis: Differential diagnoses for eosinophilic myositis include hypereosinophilic syndrome: IgE, eosinophilic leukocytes> 1.5 × 10⁹/ L, skin reaction. Multiorgan involvement, Pain and weakness in proximal muscles, Raynaud's , vasculitis in small blood vessels, CK may be elevated.
• Eosinophilic fasciitis (CK usually normal, typical findings in skin and subcutaneous tissue)
• Fibromyalgia: Very common among otherwise healthy women. General pain (chronic in both upper and lower extremities, neck or back). "Tenderpoints". Normal samples.
• Glycogen storage disease type V: McArdle's disease / phosphorylase deficiency: Pain/cramps after activity.
• Glycogen storage disease type II, Adult acid maltase deficiency (Pompe disease): Infantile, very severe form and adult, "late-onset" form with an average age of 36 years at diagnosis. Progressive loss of strength, with breathing difficulties (weak respiratory muscles).
• GVH (graft versus host) Post-transplant myositis: Most often more than one year after transplant. Findings as in myositis.
• HIV infection: Chronic weight and strength loss. Clinical picture with CK rise (inflammatory myopathy) as in myositis. HIV test. CD4 T cells correlate poorly with myopathy symptoms.
• Hypothyroidism: High TSH, Low f-T4
• Inclusion body myositis: Lower creatine kinase (CK) in blood, very slow progression, older age, distal affection, no antibody, typical biopsy
• IMNM (Immunmediated Necrotising Myositis): May be related to statins (cholesterol-lowering drugs). HMGCR antibody is present in some
• Calcinosis (columns under the skin and in soft tissue) occurs in various conditions
• Cataplexy: Sudden loss of muscle power in several fits. By narkolepisi 70% also have cataplexy.
• Kennedy disease (Spinal and bulbar muscular atrophy, SBMA): Impaired force and symmetrical muscle atrophy in proximal muscles. Creatine kinase (CK) is moderately elevated. Men aged 40-50. Reduced androgen sensitivity with gynecomastia, testes atrophy and reduced libido. Fasciculations in facial muscles. Speech and swallowing difficulties. Distinguished from myositis by clinical picture (facial muscles, gynecomastia, EMG and muscle biopsy).
• Lambert-Eaton syndrome: Myasthenia-like paraneoplastic syndrome. Eye muscles are not attacked. Antibody against voltage-gated calcium channel (VGCC) and EMG findings.
• Drug induced myopathy
  • Statins: Pain with or without elevated creatine kinase (CK) in blood. Medication history important.
  • Others: High corticosteroid doses (Prednisolone) over a long period of time. In steroid myopathy, CK is normal. Amiodarone hydrochloride (Cordarone) against heart rhythm disorders. Plaquenil. Cocaine. Alcohol. Colchicine
• Mitochondrial myopathy, encephalomyopathy, lactate acidosis, stroke-like symptoms (MELAS)
• Mitochondrial Disease
• Muscular Dystrophy (hereditary, progressive muscle diseases). Should always be considered in chronic muscle disease
• Myastenia gravis: Increased physical muscular fatigue. Often in facial muscles, including eyes. Normal CK. EMG is characteristic. Anti-acetylcholine antibodies.
• Myoclonic Epilepsy with Ragged Red Fibers» (MERRF).: "Ragged Red Fibers" are diseased mitochondria clumped together in a tissue sample (biopsy). Low body height, hearing loss, lactic acidosis, intolerance to physical exercise.
• Parkinson's disease: Trembling (tremor)
• Periodic paralysis
• Polymyalgia rheumatica: Older age, sudden onset, pronounced morning stiffness, pain and stiffness, but not primarily muscle weakness. High SR and CRP. Normal CK.
• Post-polio syndrome: 15-30 years after poliomyelitis (age 35-60). Muscle pain, weakness, exhaustion
• Rhabdomyolysis: CK is very high above 10.000 (Note! risk of kidney damage). After injury, intoxication or critical illness.
• Rhabdomyolysis and myalgia syndrome associated with RY1 mutation: Increased risk of hyperthermia. May have moderately elevated CK and muscle manifestations.
• Refsum disease: Retinitis pigmentosa. Chronic polyneuropathy with paresis. Muscle atrophy distally. Cerebellar symptoms with ataxia
• Sarkoid myopathy: Most often without symptoms. Sarcoidosis detected in other organs. Granulomas in tissue sample.
• Scleromyositis (disease with overlapping symptoms against systemic sclerosis)
• Spinal muscle atrophy: Hypertrophy of calves (Ørstavik K, 2020)
• Statin-induced myopathy
• Steroid-induced myopathy: Muscle weakness with long-term corticosteroids. Normal CK.
• Subaracnoidal hemorrhage and stroke
• Trichionose: Parasitic infection (trichines) from consumption of raw, infected (pork) meat. Strong muscle pain and enzyme (CK) rises. Eosinophilia. Muscle biopsy confirms the diagnosis.
• Viral myositis (rare) in: Influenza A and B, H1N1 virus, hepatitis (also hepatitis E), Coxsackie virus, Epstein-Barr virus, Herpes simplex virus, Parainfluenza, Adeno virus, Echovirus, Cytomegalovirus (CMV), measles virus, Varicella-Zoster, Human Immunodeficiency Virus (HIV), Dengue fever: Rapid disease development, may be limited to a few muscle groups. Effect of antiviral treatment.

Elevated creatine kinase (CK) and/or troponin in the blood

Heart attack and other heart disease. CK, CKMB and Troponin T (cTnT) is a heart muscle enzyme, but it is not specific for the heart muscle (myocardium). Troponin T is often elevated in skeletal muscle disease. Troponin T may be increased in case of heart muscle damage (heart attack, heart failure, Heart amyloidosis, Heart sarcoidosis), but also in case of stroke. Some have genetic conditions that lead to higher values ​​without concomitant disease. Troponin I (cTnI), on the other hand, is more myocardial specific (Welsh ON, 2019).

Macro-CK: Macro Enzymes are normal enzymes (or isoenzymes) that bind either to immunoglobulins (IgG) = Type 1 or lipoproteins and other substances (Type 2) and thus accumulate in serum. They are not free enzymes, but cause falsely elevated CK measurements. Macro-CK is most often seen in people over 60. Macro-CK can be present with or without associated disease, including chronic liver disease and malignancy.

Rhabdomyolysis is serious muscle damage with CK values ​​above 10.000 and risk of failure in other organs, especially the kidneys. Rhabdomyolysis is described in a separate chapter.

Accident. Physical injury, accidents, convulsions, infections, injections, metabolic myopathy and physical overload can cause very high CK values ​​in the blood.

Tringing. If creatine kinase (CK) is below 1000, the test is repeated without prior physical activity. Elevated CK levels are expected to be halved approx. every 24-36 hours if the triggering cause has been removed. Normalization within 3-5 days is expected.

Other causes of high CK er acute aortic dissection, Acute respiratory distress syndrome (ARDS), hypotension and shock, pulmonary embolism and kidney failure. Among ethnically black Africans, CK is up to 70% higher than in whites (reference: Brewster CM, 2012).

Pregnancy

Myositis that begins during pregnancy carries a risk of damage to the fetus. An increased incidence of miscarriages, stillbirths and premature births in myositis has been reported. Patients with active myositis are most at risk, while those in a quiet phase of the disease can expect a normal course of pregnancy. Nevertheless, pregnancy with myositis is generally perceived as "risk pregnancy". One should be followed up by the maternity ward and rheumatologist. Before a pregnancy, it is important that any drug use is reviewed by a specialist. In particular, it must be investigated whether the drugs can be continued during pregnancy or must be changed. In case of muscle weakness, preparation for birth by caesarean section may be relevant (reference: Ito Y, 2021). Please also see info from NKSR. Also read more about pregnancy with rheumatic diseases on its own page here.

Treatment

Before treatment is started, it is important that one is informed about the disease and what the treatment goal is, as well as side effects that may occur. Treatment goals can be to stop the disease completely, that is to achieve remission. Unfortunately, there is no treatment that cures the disease. Dermatomyositis is treated quite similarly to other types of myositis (please see treatment on the page about Myositis). The treatment must be adapted to the individual's illness and situation.

The principle is to reduce the rheumatic inflammation in muscle and possibly skin with immunosuppressive drugs (DMARDs og Biological drugs). At the beginning of the disease, high doses of cortisone may be necessary, often in the form of prednisolone. Later in the course, cortisone is reduced to a low dose or stopped altogether. Adapted physical training is also useful, but must be instructed (by a physiotherapist) so that there is no overload. It is not shown that a special diet or alternative medicines have an effect. In the case of dermatomyositis, one should be particularly careful with sunbathing (use sunscreen with a high factor). In case of severe eczema, the skin is treated by a dermatologist.

Prognosis

The course of the disease is clearly different from person to person and depending on the type of myositis present. Most people respond well to treatment and regain muscle strength within a few weeks. For others, it may take longer. The vast majority need medication for several years to prevent recurrence of the disease. The severity of the disease is often determined by whether internal organs, especially the lungs (see Antisynthetase syndrome), is the attack and whether the treatment is well tolerated.

Previously, it was estimated that approximately 1/3 improved, 1/3 did not deteriorate, while 1/3 got worse over time. However, more recent treatment has improved the prognosis. Survival depends on age, pulmonary manifestations or concomitant cancer. Five-year survival is generally estimated at approx. 95% and 10-year survival 90% (Danieli MG, 2014).

Literature

• Cassius C, 2019 (Dermatomyositis antibody)
• Leatham H, 2018 (Dermatomyositis cancer)
• Lundberg IE, 2017: (EULAR Classification of myositis) 
• Marvi U, 2012 (Clinical characteristics)
• Grans Compendium in Rheumatology

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Tips for investigating myositis

Keywords for journal writing in myositis

Keywords for referral of myositis to a specialist

Procedures for treatment and investigation: Rheumatological Association / The Norwegian Medical Association

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• Children with dermatomyositis (juvenile dermatomyositis)
• Myositis
• Bindevevssykdommer.no
• Vaskulitt.no
• revmacompendium.no