History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include family history of DM or autoimmune disease, children and age >40 years, female sex, black race, and ultraviolet radiation exposure.[7][14][15][16][23][24]

Gottron's papules

Pathognomonic of DM.

Violaceous to dusty-red flat-topped papules and plaques over the dorsal surface of knuckles (and more rarely the wrists, elbows, knees, and malleoli).[107] The surface may be slightly scaling or sometimes psoriasiform.

Telangiectasia may develop within the lesions.[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].com.bmj.content.model.Caption@463de303[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].com.bmj.content.model.Caption@7dce82b9[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].com.bmj.content.model.Caption@6d5b0e1e

heliotrope rash with or without periorbital oedema

Highly characteristic sign.

Violaceous to dusky-red rash involving periorbital skin in a symmetrical distribution. Can involve one or both eyelids and may be associated with periorbital oedema.[108][109][110] May be subtle and wax and wane.

macular violaceous erythema

Symmetrical violaceous erythematous macular rash with characteristic distributions:[108][109][110]

Gottron's sign: macular patches over knuckles, elbows, and knees.

V-sign: distribution in 'v' of neck and upper chest indicating photodistribution.

Shawl sign: distribution in nape of neck, posterior shoulders, and upper back.

Holster's sign: distribution on lateral thigh or hip.

Linear extensor erythemas: involving extensor surfaces of legs, thighs, upper arms, forearms, dorsal fingers, and feet.

Facial rash can also be seen in malar distribution with perioral sparing.

Erythema involving the scalp is often associated with pruritus.[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].com.bmj.content.model.Caption@31ab48e0

periungual erythema, nail-fold capillary dilation, cuticular overgrowth

Commonly seen, although also present in other connective tissue disorders.[70][71]

Dilated capillary loops with vascular drop-out and cuticular overgrowth (ragged cuticles) can be indicators of disease activity.[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].com.bmj.content.model.Caption@186854a

'mechanic's' hands

Hyper-keratosis, scaling and fissuring of palms of hands and palmar aspect of fingers.[45]

May be part of the anti-synthetase syndrome.

proximal muscle weakness

The onset of muscle weakness is usually subacute. Weakness is proximal and symmetrical (e.g., difficulty getting out of a chair, climbing stairs, washing/combing hair, and lifting arms).

Distal motor involvement is present in only 10% to 20% of cases and is more likely in later disease.[73]

Other diagnostic factors

common

photosensitivity

Patients may not offer a history of photosensitivity, but skin involvement is more pronounced on sun-exposed areas.[66][67]

There are reports of worsening of skin lesions with sun exposure and this may result in tense blistering.

poikiloderma vasculare atrophicans

Non-specific sign.

Atrophic areas with varying hypo-pigmentation and hyper-pigmentation, telangiectasia, and scaling.

May occur in areas of chronic macular violaceous erythema.

pruritus

May be a prominent symptom, especially with scalp involvement. Its presence may help differentiate between DM and cutaneous lupus.[108]

fatigue and malaise

Common but non-specific symptom.

dyspnoea

May be secondary to respiratory muscle weakness, interstitial lung disease, or cardiac involvement.[76][77][78][111]

weight loss

May be reported along with other constitutional symptoms. Significant weight loss, however, is not common and when present should raise the possibility of malignancy-associated DM.

uncommon

fever

Non-specific symptom.

myalgia

Present in approximately 30% of patients.[3]

arthralgia

Polyarthralgia or polyarthritis may be present in a rheumatoid arthritis type distribution.[74][75]

A deforming arthritis is rarely seen but may occur as part of the anti-synthetase syndrome.[75]

dysphagia

Present in 15% to 50% of patients, oesophageal disease is a poor prognostic sign.

Proximal dysphagia due to involvement of pharyngeal and oesophageal striated muscle correlates with severity of muscle involvement elsewhere and responds to treatment.

Distal dysphagia is due to non-striated muscle disease and is more common in patients with overlap syndromes, especially in overlap with systemic sclerosis.[110]

palpitations and syncope

Cardiac involvement occurs in 50% of patients but is rarely symptomatic unless disease is advanced.[79] Arrhythmias are the most common cardiac abnormality and these may be symptomatic.[80] Cardiac failure due to cardiac myositis is rare.

Clinically apparent cardiac involvement is a poor prognostic indicator.[77][78]

Raynaud's phenomenon

More common in overlap DM and a feature of the anti-synthetase syndrome.[73][112]

cutaneous calcinosis

Rare in adult patients but present in approximately 30% to 70% of children with DM.[48][68][69]

Subcutaneous, firm, yellow- or flesh-coloured nodules, often over bony prominences.

Complications include extrusion with secondary infection.

Calcinosis in juvenile DM can be extensive, resulting in contractures and loss of function.

erythroderma

Total-body erythema is a rare manifestation.

vesiculobullous lesions

May be more common in malignancy-associated DM.

leukocytoclastic vasculitis

Rare manifestation. When present suggests malignancy-associated DM.[113]

cutaneous necrosis

Rare manifestation. When present suggests malignancy-associated DM.[114]

non-scarring alopecia

When present may be a sign of disease flare.[110]

Risk factors

strong

genetic predisposition

Suggested by the occurrence in monozygotic twins, familial cases, and familial association with other autoimmune diseases.[14][15][16]

There are reported associations between DM/polymyositis (PM) and HLA-DRB1*03 in white people and HLA-DRB1*14 in Koreans.[19][20] HLA-DRB1*09:01 and HLA-DRB1*12:01 alleles may contribute to susceptibility to adult DM in the Han Chinese population.[17]

HLA-DQA1 0501 is reported to be associated with juvenile DM and tumour necrosis factor 308A polymorphism with photosensitivity in DM.[18][21]

bimodal age distribution: children and age >40 years

There are two peaks of incidence: between 5 and 15 years of age and between 40 and 60 years.[5][6][7]

female sex

Adult-onset DM has a female preponderance of approximately 2.5:1.[7][8]

black race

DM is more common in the black population than in the white population.[7][8]

ultraviolet radiation

The rash is often photodistributed, developing in sun-exposed areas. Some patients report sensitivity to sunlight, although others do not make this association.[58]

Increased ultraviolet-light-induced apoptotic cells in the skin may lead to supra-threshold concentration of antigenic peptides.[59] Ultraviolet-radiation intensity has been shown to be a strong contributor to DM and is related to the proportion of anti-Mi-2 antibodies.[22][23][24]

weak

infectious agents

Direct muscle invasion by bacteria and viruses causing myositis is well recognised. Although no good evidence is available for infectious agents as environmental triggers, some findings may support this hypothesis.[13]

There are some reports of DM/polymyositis developing in patients with antibodies to Borrelia burgdorferi and Toxoplasma gondii.[25][26]

High titres of coxsackievirus antibodies have been found in cases of idiopathic inflammatory myopathies early in disease course.[27][28] Picornavirus-like particles have been found in muscle biopsies of patients with myositis.[29]

drugs

Drugs that have been implicated in causing DM include D-penicillamine, hydroxyurea, statins, phenylbutazone, and terbinafine.[36][37][38][39][40][41][42][43][44]

The most commonly reported are statins (HMG-CoA reductase inhibitors), including simvastatin, lovastatin, and fluvastatin.[39][40][41][42] These reports are rare and statins are more likely to be associated with myalgia and minor elevations of creatine kinase (CK) rather than myositis per se.

immunisation

There have been case reports following immunisation against tetanus, tuberculosis, and diphtheria, and following combined immunisation against typhoid, cholera, and polio.[60][61][62][63]

Population studies have not shown an association between immunisation and DM.[21]

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