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# Dermatomyositis and antisynthetase syndrome

- Lesion

In dermatomyositis, immune injury to small vessels causes skin rash and weakness at the edges of muscle bundles; some cases signal a hidden cancer.

Updated Nov 12, 2026

## Key points

- Skin: heliotrope rash of the eyelids with oedema, Gottron papules over the knuckles, shawl and V signs, nail-fold capillary changes, calcinosis (juvenile form).
- Weakness: symmetric proximal, slow onset; dysphagia; CK raised.
- Biopsy hallmark: perifascicular atrophy, perimysial and perivascular inflammation (CD4 T cells, B cells, plasmacytoid dendritic cells), MxA expression, MAC on capillaries.
- Adult dermatomyositis carries a raised cancer risk (ovary, lung, stomach, nasopharynx in Asia), especially with anti-TIF1-γ.
- Anti-MDA5: amyopathic disease with rapidly progressive interstitial lung disease and skin ulcers.
- Antisynthetase (anti-Jo-1): ILD, myositis, arthritis, Raynaud, fever, mechanic's hands; perifascicular necrosis on biopsy.

## What it is

Dermatomyositis is an autoimmune disease of skin and muscle in children and adults. Type I interferon signaling, complement deposition on endomysial capillaries and capillary loss injure the edges of muscle fascicles, producing perifascicular atrophy. Patients have proximal weakness with characteristic skin signs. Myositis-specific autoantibodies define subgroups: anti-Mi-2 (classic skin and muscle disease), anti-MDA5 (rapid interstitial lung disease, little myositis), anti-TIF1-γ and anti-NXP2 (cancer in adults). Antisynthetase syndrome, with antibodies against aminoacyl-tRNA synthetases such as Jo-1, combines myositis with interstitial lung disease, arthritis, Raynaud phenomenon, fever and 'mechanic's hands'.

## Structure

- Perifascicular atrophy: small, degenerating fibres along the edges of fascicles where capillary loss is greatest.
- Inflammation is perimysial and perivascular rather than inside fascicles.
- Membrane attack complex deposited on endomysial capillaries; reduced capillary density.
- Type I interferon-induced proteins such as MxA in perifascicular fibres.
- Skin: interface dermatitis with mucin, similar to lupus.

## Step by step

- Genetic risk and triggers (UV light, infections, tumour antigens) start an autoimmune response.
- Plasmacytoid dendritic cells produce type I interferon, which induces interferon-stimulated genes in muscle and vessels.
- Antibody and complement damage endomysial capillaries, which drop out.
- Fibres at the edges of fascicles, farthest from surviving vessels, become ischaemic and atrophic.
- In antisynthetase syndrome, immunity against tRNA synthetases injures lung and muscle together.

## Autoantibodies of dermatomyositis and related myositis

| Antibody | Phenotype | Note |
| --- | --- | --- |
| [Anti-Mi-2](https://durgical.com/en/conditions/inflammatory-myopathies/) | Classic skin and muscle disease | Good response to treatment |
| [Anti-MDA5](https://durgical.com/en/conditions/interstitial-lung-disease/) | Little myositis, rapid ILD, skin ulcers | High mortality from lung disease |
| [Anti-TIF1-γ](https://durgical.com/en/conditions/paraneoplastic-syndromes/) | Severe skin disease | Strong cancer association in adults |
| Anti-NXP2 | Calcinosis, juvenile disease | Cancer link in adults |
| Anti-Jo-1 and other synthetases | Antisynthetase syndrome | ILD, arthritis, mechanic's hands |

## Clinical notes

- A new diagnosis of adult dermatomyositis calls for age-appropriate cancer screening, repeated over the first years.
- Lung function and chest CT screen for interstitial lung disease, the main cause of death in antisynthetase and anti-MDA5 disease.
- Treatment is immunosuppression with glucocorticoids and steroid-sparing agents.

## Memory aid

Dermatomyositis damages the vessels at the borders, so the fibres at the border fade.

## Test yourself

Think of the answer, then tap the question to see it.

## What is perifascicular atrophy?

Atrophy of fibres at the edges of muscle fascicles, the biopsy hallmark of dermatomyositis.

## Which skin signs are typical of dermatomyositis?

Heliotrope rash of the eyelids, Gottron papules over the knuckles, shawl and V signs.

## Which antibody is linked to cancer-associated dermatomyositis?

Anti-TIF1-γ (also anti-NXP2).

## What features define antisynthetase syndrome?

Antisynthetase antibodies such as anti-Jo-1 with myositis, interstitial lung disease, arthritis, Raynaud and mechanic's hands.

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## Elsewhere in DurgiPedia

- [Type I interferons (α, β)](https://durgical.com/en/immunology/type-i-interferons/)
- [Autoantibodies: the table to know](https://durgical.com/en/immunology/autoantibodies-the-table-to-know/)
- [Complement: three pathways, MAC, regulators](https://durgical.com/en/immunology/complement-three-pathways-mac-regulators/)

## Connections

## Related 4

- [Necrotizing myopathy, inclusion body myositis and polymyositis](https://durgical.com/en/general-pathology/necrotizing-myopathy-inclusion-body-myositis-and-polymyositis/)
- [Reading a muscle biopsy: neurogenic vs myopathic](https://durgical.com/en/general-pathology/reading-a-muscle-biopsy-neurogenic-vs-myopathic/)
- [The lung in autoimmune disease](https://durgical.com/en/general-pathology/the-lung-in-autoimmune-disease/)
- [Paraneoplastic syndromes: the table to know](https://durgical.com/en/general-pathology/paraneoplastic-syndromes-the-table-to-know/)

## Related conditions 3

- [Inflammatory myopathies (dermatomyositis, polymyositis)](https://durgical.com/en/conditions/inflammatory-myopathies/)
- [Interstitial lung disease](https://durgical.com/en/conditions/interstitial-lung-disease/)
- [Paraneoplastic syndromes](https://durgical.com/en/conditions/paraneoplastic-syndromes/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Myositis | Polymyositis | Dermatomyositis | MedlinePlus](https://medlineplus.gov/myositis.html) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/dermatomyositis-and-antisynthetase-syndrome/