Cutaneous Lupus and Dermatomyositis Skin Signs
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Direct answer
Cutaneous lupus and dermatomyositis produce characteristic skin signs that point toward the diagnosis: the malar rash of systemic lupus, and the heliotrope rash and Gottron papules of dermatomyositis. Discoid plaques with atrophic scarring are the hallmark of chronic cutaneous lupus, while the shawl sign and mechanic's hands also favour dermatomyositis. Recognising these markers directs antibody testing, muscle assessment and a search for malignancy in adults.
What you must remember
- Malar rash: fixed erythema over the cheeks and nose that spares the nasolabial folds; a feature of systemic lupus erythematosus.
- Discoid lesions: well-demarcated plaques with follicular plugging and atrophic scarring, the hallmark of chronic cutaneous lupus.
- Subacute cutaneous lupus: annular or polycyclic photosensitive lesions, associated with anti-Ro (SSA) antibodies.
- Heliotrope rash: violaceous periorbital erythema with oedema, a skin marker of dermatomyositis.
- Gottron papules: violaceous papules over the knuckles, elbows and knees, with Gottron sign as erythema over the extensor surfaces.
- Shawl sign: erythema over the neck, shoulders and upper back, distributed like a shawl.
- Mechanic's hands: hyperkeratotic, fissured fingertips, often linked with anti-synthetase antibodies.
- Malignancy link: adults with dermatomyositis need age-appropriate cancer screening, particularly for ovarian, lung and gastric cancers.
Points that get misassigned
Most questions test whether a skin sign has been assigned to the correct disease.
- Trap: calling a malar rash a sign of dermatomyositis Correct: the malar rash belongs to systemic lupus, whereas the heliotrope rash and Gottron papules belong to dermatomyositis.
- Trap: diagnosing dermatomyositis from the skin alone Correct: confirm with creatine kinase, electromyography, MRI or muscle biopsy, because the rash is supportive rather than diagnostic.
- Trap: skipping cancer screening in an adult with dermatomyositis Correct: adult dermatomyositis carries a malignancy association, so age-appropriate screening is required.
- Trap: treating discoid lesions with systemic steroids alone Correct: discoid lesions respond to topical steroids, sun protection and hydroxychloroquine, and systemic steroids are reserved for systemic disease.
Frequently asked questions
Which skin sign separates systemic lupus from dermatomyositis on the face?
The malar rash of systemic lupus erythematosus is a fixed erythema over the cheeks and nose that spares the nasolabial folds. The heliotrope rash of dermatomyositis is violaceous periorbital erythema with oedema. Recognising which pattern is present narrows the antibody testing that follows.
What is the shawl sign and which disease does it indicate?
The shawl sign is erythema over the neck, shoulders and upper back, distributed like a shawl. It is a cutaneous marker of dermatomyositis. Its presence should prompt a check of muscle strength and creatine kinase.
Which antibody is linked with subacute cutaneous lupus?
Subacute cutaneous lupus is associated with anti-Ro (SSA) antibodies. Its lesions are annular or polycyclic, photosensitive and found on sun-exposed skin. Anti-Ro antibodies also link the condition with neonatal lupus.
Why should adults with dermatomyositis be screened for cancer?
Dermatomyositis in adults is associated with an increased risk of underlying malignancy, particularly ovarian, lung and gastric cancers. Screening is age-appropriate and includes a thorough history, examination and targeted investigations. Anti-TIF1-gamma antibodies are a particularly strong marker of this association.