Polymyositis and Dermatomyositis

British Society for Rheumatology guideline on management of paediatric, adolescent and adult patients with idiopathic inflammatory myopathy. Published: Mar 2022.

Article Last Updated:25/07/2026

Dermatomyositis and Polymyositis

Causes and Risk Factors

The exact underlying cause is unknown. Dermatomyositis and polymyositis are considered autoimmune conditions triggered by an interaction between genetic susceptibility and environmental factors ^[Ref1]^[Ref2]

Genetic factors (e.g. DRB1*0301, DRB1*11:01)
Demographic factors
- Females
- More common in African-American
- Dermatomyositis affects both children and adults, but polymyositis almost exclusively affects adults
Environmental triggers
- Viral infections (esp. HIV and HTLV-1)
- Bacterial and parasitic infections (e.g. Borrelia burgdorferi, streptococci)
- Drugs (e.g. penicillamine, zidovudine)

Clinical Manifestation

Shared features of dermatomyositis and polymyositis: ^[Ref1]^[Ref2]

MSK manifestation

Hallmark: subacute, progressive symmetrical proximal muscle weakness

The shoulders and pelvic girdle are often first affected
This often causes difficulty in standing up from a seated position, climbing stairs, and lifting objects

Other muscle involvement:

Weakness of neck flexors is common (severe weakness can cause a “dropped head syndrome”)
Advanced cases
- Weakness of the pharyngeal muscles → dysphagia, hoarseness, nasal regurgitation
- Weakness of the respiratory muscles → respiratory failure

Symptoms:

Significant myalgia is uncommon
Sensation and reflexes are normal

Extra-MSK manifestation

Systemic features
- Fever
- Weight loss
- Malaise
- Arthralgia
- Raynaud phenomenon
Interstitial lung disease – major complication and carries a poor prognosis
Cardiac involvement (e.g. AV block, arrhythmia, myocarditis, heart failure)

Type-specific features: ^[Ref1]^[Ref2]

Dermatomyositis	Polymyositis
Dermatomyositis affects both adults and children As suggested by its name “dermato…”, it is characterised by the presence of skin rashes: Gottron papules (raised, violaceous / purple papules over the knuckles) – pathognomonic Heliotrope rash (violaceous / purple discolouration of the upper eyelids +/- periorbital oedema) V sign (photosensitive erythematous rash over the anterior neck and upper chest in a V-shaped distribution) Shawl sign (photosensitive erythematous rash over the upper back, posterior neck and shoulders) Gottron sign (flat violaceous or erythematous rash over extensor joint surfaces) Up to 20% of dermatomyositis may present with the characteristic skin rashes and biopsy findings but without muscle weakness (amyopathic presentation) Other possible features: Mechanic’s hands (rough, cracked skin on the palms) Periungual telangiectasias Calcinosis (calcium deposition in subcutaneous tissue that appears as hard, raised, white, or yellow nodules +/- chalky white material) Dermatomyositis is strongly associated with underlying cancers Notable malignancies include ovarian, lung, breast, GI cancers, and non-Hodgkin lymphomas ~15% of adults with dermatomyositis have a pre-existing malignancy or will develop one In children, there is a significantly increased risk of leukaemia and lymphoma	Polymyositis almost exclusively affects adults Absence of skin rashes seen in dermatomyositis

Dermatomyositis

Polymyositis

Dermatomyositis affects both adults and children

As suggested by its name “dermato…”, it is characterised by the presence of skin rashes:

Gottron papules (raised, violaceous / purple papules over the knuckles) – pathognomonic
Heliotrope rash (violaceous / purple discolouration of the upper eyelids +/- periorbital oedema)
V sign (photosensitive erythematous rash over the anterior neck and upper chest in a V-shaped distribution)
Shawl sign (photosensitive erythematous rash over the upper back, posterior neck and shoulders)
Gottron sign (flat violaceous or erythematous rash over extensor joint surfaces)

Up to 20% of dermatomyositis may present with the characteristic skin rashes and biopsy findings but without muscle weakness (amyopathic presentation)

Other possible features:

Mechanic’s hands (rough, cracked skin on the palms)
Periungual telangiectasias
Calcinosis (calcium deposition in subcutaneous tissue that appears as hard, raised, white, or yellow nodules +/- chalky white material)

Dermatomyositis is strongly associated with underlying cancers

Notable malignancies include ovarian, lung, breast, GI cancers, and non-Hodgkin lymphomas
~15% of adults with dermatomyositis have a pre-existing malignancy or will develop one
In children, there is a significantly increased risk of leukaemia and lymphoma

Polymyositis almost exclusively affects adults

Absence of skin rashes seen in dermatomyositis

Investigation and Diagnosis

Both dermatomyositis and polymyositis share the same diagnostic work-up but with different diagnostic findings: ^[Ref1]^[Ref2]

Investigation	Findings in dermatomyositis	Findings in polymyositis
Serum creatine kinase (CK)	↑ Creatine kinase in most cases (completely normal in some cases despite active disease)	↑ Creatine kinase
Serology (antibodies)	Myositis-specific autoantibodies (MSAs), including Anti-Jo-1 (the most common anti-synthetase antibody) Anti-Mi-2 Anti-MDA5 Anti-NXP2 and anti-TIF1-γ Myositis-associated antibodies (MAAs), including Anti-snRNPs Anti-PM-Scl Anti-Ro, anti-La, anti-Ku Anti-KL6 Antibodies and correlations: Anti-MDA5 is exclusively seen in dermatomyositis Anti-Mi-2 and anti-Jo-1 (and other anti-synthetase antibodies) are found in either dermatomyositis or polymyositis Anti-PM-Scl is highly indicative of an overlap syndrome (with systemic sclerosis or having both dermatomyositis and polymyositis) The following antibodies are strongly associated with the development of interstitial lung disease Anti-Jo-1 and other anti-synthetase antibodies Anti-MDA5 (also associated with a rapidly progressive and severe form of interstitial lung disease) The following antibodies are associated with malignancy risk Anti-NXP2 Anti-TIF1-γ
EMG	Dermatomyositis and polymyositis may demonstrate myopathic findings EMG helps distinguish myopathic from neurogenic causes of weakness (e.g. peripheral neuropathy, motor neuron disease)
MRI	Used to detect muscle inflammation, necrosis and degeneration Identifies the most actively involved muscle to guide biopsy Monitor response to therapy
Definitive test: muscle biopsy	Perifascicular atrophy (atrophic fibres found at the periphery of the fascicles) Inflammatory infiltrates are predominantly perivascular and perimysial, consisting mostly of B cells and CD4+ T cells Periendomysial membrane-attack complex (MAC) deposition leading to capillary necrosis and muscle ischemia	No specific distribution of atrophy (scattered atrophy with size variations) Inflammatory infiltrates are predominantly endomysial, consisting mostly of CD8+ T cells
Definitive test: muscle biopsy	Rimmed vacuoles and intracellular amyloid/protein deposits are typically absent in dermatomyositis and polymyositis. Their presence should raise suspicion for inclusion-body myositis (see below for more information)

Management

All patients should receive an individually tailored exercise program led by a specialist physiotherapist or occupational therapist

Cornerstone pharmacological management:

Induction therapy (to treat active myositis) with high-dose steroids (oral prednisolone or IV methylprednisolone)
Long-term maintenance therapy (to achieve clinical remission and reduce long-term side effects of steroids): DMARDs
- In adults: methotrexate, azathioprine, tacrolimus, ciclosporin, or mycophenolate mofetil
- In children: methotrexate is recommended to be combined with high-dose steroids from the start

Options for severe or refractory disease: IVIG, rituximab, cyclophosphamide, abatacept

Most patients with dermatomyositis and polymyositis respond well to high-dose steroids

A patient diagnosed with polymyositis who shows no clinical improvement in muscle strength after 2-3 months of high-dose steroids should raise suspicion of inclusion body myositis (see below for more details), due to rarity of polymyositis and high rates of misdiagnosis.

Management of other manifestations:

Skin manifestation in dermatomyositis
- Sun avoidance
- Use of high-factor sun cream
Interstitial lung disease
- Induction with steroids plus tacrolimus / ciclosporin / cyclophosphamide / rituximab
- Maintenance with a DMARD

Differential Diagnosis – Inclusion-Body Myositis

Inclusion-body myositis is another idiopathic inflammatory myositis, but is considered a completely distinct clinicopathologic entity from dermatomyositis and polymyositis. ^[Ref1]^[Ref2]

Clinical features

More common in >50 y/o males
Asymmetrical distal weakness (esp. wrist and finger flexors)
Early involvement of the lower limb (esp. quadriceps, ankle dorsiflexors) → falls and buckling of the knees

Inclusion body myositis should be suspected in patients who are initially diagnosed with polymyositis who fail to improve with 2-3 months of steroids

Investigation and diagnosis

Associated with anti-cytosolic 5-nucleotidase 1A (NT5C1A) antibodies
Creatine kinase is typically normal or mildly elevated
Muscle biopsy uniquely shows rimmed vacuoles and amyloid deposition

Management

Inclusion-body myositis is difficult to treat and has a poor response to standard immunosuppressive therapies

References

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Polymyositis and Dermatomyositis

Dermatomyositis and Polymyositis

Causes and Risk Factors

Clinical Manifestation

Investigation and Diagnosis

Management

Differential Diagnosis – Inclusion-Body Myositis

References

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