Dermatomyositis

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Muscle and cutaneous involvement develop simultaneously in approximately 60% of patients, although in 30% skin lesions precede muscle weakness.[64] In some patients the delay between cutaneous lesions and symptoms of muscle weakness may be several months.[65] Between 10% and 20% of patients have typical skin lesions but never develop clinically apparent muscle disease.[2]

History

The cardinal musculoskeletal symptom is subacute proximal muscle weakness affecting the arms and legs. Patients report difficulty rising from a chair, climbing stairs, and washing or combing their hair. Myalgia is present in <30% of patients.[3]

Distal motor weakness is a rare and late feature and raises the possibility of inclusion body myositis as an alternative diagnosis. Extraocular muscles are not affected.[54]

Patients may present with a variety of cutaneous manifestations (see Physical examination).

Patients may describe severe photosensitivity with blistering and pruritus.[66][67] Other less common symptoms reported by the patient may include:[3]

fatigue
fever
arthralgia
Raynaud's phenomenon
breathlessness
dysphagia
dysphonia
symptoms of cardiac failure.

In malignancy-associated DM, patients may also report a range of symptoms relating to the underlying malignancy.

Physical examination

The clinical feature that differentiates DM from other inflammatory myopathies is the presence of characteristic skin involvement.[1]

Cutaneous manifestations

Heliotrope rash: periorbital dusky violaceous erythema of the eyelids often associated with periorbital oedema.
Gottron's papules: pathognomonic of DM. Violaceous flat-topped papules and plaques on the dorsal surfaces of the knuckles, and more rarely the wrists, elbows, knees, and malleoli.[Figure caption and citation for the preceding image starts]: Macular erythematous patches (Gottron’s papules) over the dorsal surface of the hands, especially over the metacarpophalangeal and proximal interphalangeal jointsAdapted from BMJ Case Reports 2009 [doi:10.1136/bcr.06.2009.2027] Copyright © 2009 by the BMJ Publishing Group Ltd [Citation ends].[Figure caption and citation for the preceding image starts]: Macular erythematous patches (Gottron’s papules) over the elbowsAdapted from BMJ Case Reports 2009 [doi:10.1136/bcr.06.2009.2027] Copyright © 2009 by the BMJ Publishing Group Ltd [Citation ends].[Figure caption and citation for the preceding image starts]: Macular erythematous patches (Gottron’s papules) over the kneesAdapted from BMJ Case Reports 2009 [doi:10.1136/bcr.06.2009.2027] Copyright © 2009 by the BMJ Publishing Group Ltd [Citation ends].
Macular violaceous erythemas: classic distributions include V sign (neck and upper chest area), shawl sign (nape of neck, posterior shoulders, and upper back), Gottron's sign (knuckles, elbows, and knees). Atrophic areas with varying hypo-pigmentation and hyper-pigmentation, telangiectasis, and scaling (poikiloderma vasculare atrophicans) may occur in areas of chronic macular violaceous erythema.
Hyper-keratosis, scaling, and fissuring of palms of hands and palmar aspect of fingers: commonly referred to as 'mechanic's' hands and associated with anti-synthetase syndrome.[45]
Cutaneous calcinosis: seen in 30% to 70% of juvenile DM; rare in adult DM and associated with anti-NXP2 antibodies.[48][68][69][Figure caption and citation for the preceding image starts]: Macular erythematous patches (Gottron’s papules) over the toes with dystrophic cuticlesAdapted from BMJ Case Reports 2009 [doi:10.1136/bcr.06.2009.2027] Copyright © 2009 by the BMJ Publishing Group Ltd [Citation ends].

Examination of the nails may identify periungual erythema, nail-fold capillary dilation with occasional vascular drop out, and cuticular overgrowth (ragged cuticles). Although these nail changes can be seen in other connective tissue diseases, they occur most commonly in DM.[70][71]

Skin involvement often causes significant morbidity and can persist despite good control of muscle disease.[72]

Muscle involvement

Symmetrical proximal muscle weakness is present in patients with muscle involvement; the severity varies between patients. Muscle tenderness is present in approximately 50% of patients.

Weakness of the neck flexors can result in difficulty raising the head, and bulbar involvement may lead to hoarseness, dysphonia, or nasal regurgitation.

Breathlessness may be observed during examination. When due to respiratory muscle weakness, chest expansion and air entry may be reduced.

Muscle atrophy can be seen in long-standing disease, but severe muscle atrophy is not common and alternative diagnoses should be considered when it is present.[73]

Systemic manifestations

Inflammatory polyarthritis may occur and, when present, has a similar distribution to rheumatoid arthritis.[74] Joint involvement is more common when DM is part of an overlap with other connective tissue diseases. Severe deforming arthritis is more likely to be a feature of polymyositis.[75]

In the presence of associated interstitial lung disease, fine bilateral crepitations may be heard on auscultation.[76]

Signs of cardiac failure can be present (tachycardia, raised jugular venous pressure, gallop rhythm, and oedema) when there is cardiac involvement; however, this is uncommon, and is a poor prognostic indicator.[77][78][79][80]

Raynaud's phenomenon may be observed but is more common in overlap DM.[81]

Diagnostic investigations

The initial order of investigations will be influenced by whether the patient presents with cutaneous symptoms, muscle symptoms, or both.

Patients with clinically amyopathic dermatomyositis (CADM) need evaluation for subclinical muscle disease. This should be sought by performing creatine kinase (CK) measurement, electromyogram, muscle biopsy, and magnetic resonance imaging (MRI).[82]

Serum creatine kinase (CK) and serum aldolase

As the most sensitive muscle enzyme test, CK should be ordered for any patient with suspected DM, even if the patient presents with only cutaneous involvement, as CK may be elevated in CADM.[2][83]

Serum aldolase is a glycolytic pathway enzyme found in all tissues but mainly skeletal muscle, brain, and liver. It is not as specific or sensitive as CK for muscle disease, but is occasionally elevated in myositis when CK is normal.

Muscle biopsy

Muscle biopsy should be performed in all cases of suspected DM. In symptomatic patients, the biopsy should be taken from a weak, but not severely atrophied, muscle. Quadriceps and deltoid are common sites.

Open surgical biopsy provides a larger specimen compared with closed needle biopsy. Biopsy using a conchotome also yields useful specimens.[84] Correct processing and interpretation by a laboratory experienced in muscle histology is essential for correct diagnosis.

Electromyography (EMG)

EMG is recommended, but it is not essential, for diagnosis if raised CK and typical muscle biopsy findings are present. The EMG abnormalities are not specific but are seen more frequently in idiopathic inflammatory myopathies.[85][86] Similar patterns may be seen in toxic, infectious, or metabolic myopathies.

Skin biopsy

Skin biopsy is required to confirm diagnosis in CADM, where overlap connective tissue disease may be present, or in cases where the cutaneous diagnosis is in doubt. In patients who present with classic DM and the diagnosis is confirmed by raised muscle enzymes and muscle biopsy, skin biopsy may not be required.

Antinuclear antibody (ANA)

Positive in approximately 80% of patients.[87] Non-specific and commonly positive in other connective tissue diseases where myositis may be a feature. Further testing for autoantibodies against specific nuclear antigens (e.g., anti-double-stranded DNA, anti-Ro, anti-La, anti-Sm, anti-ribonucleoprotein [RNP]) is useful to help differentiate between DM and other connective tissue diseases, especially cutaneous lupus, which has a similar biopsy appearance.

Myositis-specific antibodies (MSAs) and myositis-associated antibodies (MAAs)

MSAs and MAAs are found in most patients with DM and are associated with clinical subsets that have varying presentations, clinical courses, and therapeutic responses.[24][88][89] They are increasingly used in clinical practice, although are not widely available.[50] Most are directed against cytoplasmic RNA-protein complexes.[46]

Anti-Mi-2 antibodies are directed against a helicase involved in transcriptional activation.[90] They are strongly associated with the classical presentation of DM but are found in only approximately 10% of patients.[91] This subset of patients have the highest response to steroid treatment and the lowest incidence of malignancy. Anti‐U1 RNP and anti‐Ku are found in overlap syndromes that present similarly to anti-Mi-2 positive DM.[50]
Anti‐transcription intermediary factor 1 gamma (TIF1-gamma) is the most commonly isolated antibody.[88] It is strongly associated with malignancy and therefore an intensive search for cancer and careful follow‐up is recommended.[45][92] The rash is often refractory to treatment.
Anti-signal recognition particle (SRP) antibodies are found almost exclusively in polymyositis and occasionally in DM. When present they are associated with acute severe, treatment-resistant necrotising myositis.[46] Immunosuppressive drugs, intravenous immunoglobulin, or rituximab are often required at an early disease stage.[93]
Anti-Jo-1 and other anti-aminoacyl-tRNA synthetase antibodies (anti-ARS antibodies; including anti‐PL‐7, anti‐PL‐12, anti‐EJ, anti‐OJ, and anti‐KS) result in a distinct clinical picture known as anti-synthetase syndrome. The main clinical features include interstitial lung disease, fever, myositis, polyarthritis, mechanic's hands, and Raynaud's phenomenon. Anti-Jo-1 is associated with a higher frequency of myositis, whereas the other anti-ARS antibodies are associated with higher frequency of interstitial lung disease. Anti-synthetase syndrome is often steroid resistant and concomitant use of immunosuppressive drugs required.[45]
Anti-melanoma differentiation-associated gene 5 (MDA5; also known as CADM‐140) is specific to CADM and is strongly associated with a rapidly progressive interstitial lung disease with poor prognosis. Tender palm papules and diffuse alopecia may be present. Patients often require treatment with immunosuppressive drugs as well as high‐dose systemic steroids from an early disease stage.[47]
Anti-NXP2 is strongly associated with juvenile DM with a high proportion suffering from cutaneous calcinosis due to dystrophic calcification.[48]
Anti-PM-Scl antibodies have been found in patients with overlapping myositis and scleroderma.[49]

Muscle magnetic resonance imaging (MRI)

MRI may improve biopsy yield by identifying affected muscles to target for biopsy.[94]

MRI findings are not specific and biopsy is required for diagnosis.[95]

Serial MRI measurements may also be performed to assess response to treatment.

Screening for major organ involvement and determining prognosis

Patients with classic dermatomyositis (CDM) or amyopathic dermatomyositis (ADM) should be investigated for occult malignancy and other disease manifestations such as myocardial involvement and interstitial lung disease.[2][82][96][97]

Electrocardiogram (ECG)

Should be performed in all patients. Around 30% of patients with idiopathic inflammatory myopathies may have ECG abnormalities.[80]

Patients with normal resting ECG but symptoms of palpitations or syncope merit further investigation with ambulatory ECG.

Echocardiography

Should be performed in all patients. Myocardial involvement severe enough to cause congestive cardiac failure is rare (<5% of patients), but when present indicates poor prognosis.[77]

Chest x-ray

Required in all patients to evaluate respiratory involvement and to screen for malignancy. In early interstitial lung disease, radiographical changes may be minimal or non-specific and interstitial lung disease may be missed if further respiratory investigations are not performed.

Cardiac troponin I

A sensitive and specific marker of cardiac damage, cardiac troponin I is used to screen asymptomatic patients at presentation with idiopathic inflammatory myopathies.[98]

Pulmonary function tests (PFTs)

Required in all patients to evaluate for respiratory muscle weakness and interstitial lung disease.[99]

High-resolution CT of chest

Should be performed in all patients to evaluate for interstitial lung disease.[99]

More sensitive than chest x-ray in detecting interstitial lung disease and provides information on prognosis not provided by chest x-ray. The presence of ground glass opacification is associated with a better prognosis compared with honeycomb fibrotic changes.[100][101]

Barium swallow or video-fluoroscopic assessment of swallow

Should be performed in patients with dysphagia, nasal regurgitation of fluid, or dysphonia.

Silent aspiration may also occur and further assessment is indicated in patients presenting with lower respiratory tract infection.[102]

Investigations for associated malignancy

Full blood count, serum ferritin, serum biochemistry screen
Urinalysis
Faecal occult blood testing
Chest x-ray
Women: mammography, CA-125, and pelvic ultrasound
Men: prostate-specific antigen
CT chest/abdomen/pelvis
Other investigations (e.g., gastrointestinal endoscopy) guided by symptoms and abnormal results.[103][104][105][106]

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