Autoimmune and Connective Tissue Diseases with Cutaneous Manifestations
The interface and the antibody
Connective tissue diseases produce cutaneous disease through interface dermatitis, mucin deposition, vasculopathy, and autoantibody-mediated injury. Learn each disease's signature lesion, distribution, and serologic marker.
Concepts to master
- Lupus erythematosus: acute (malar rash sparing nasolabial folds), subacute (annular or papulosquamous photodistributed lesions, anti-Ro/SSA), and chronic discoid (scarring plaques with follicular plugging).
- Dermatomyositis: heliotrope rash, Gottron papules over the knuckles, shawl sign, and proximal muscle weakness; anti-Mi-2, anti-TIF1-gamma, anti-MDA5 (with rapidly progressive interstitial lung disease).
- Systemic sclerosis: Raynaud phenomenon, sclerodactyly, digital ulcers, mat telangiectasias, and calcinosis.
- Morphea: localized sclerosis without systemic involvement; distinguish from systemic sclerosis.
- Sjögren syndrome: annular erythema and photosensitivity with anti-Ro/SSA.
Traps
A malar rash that spares the nasolabial folds favors lupus; seborrheic dermatitis involves the folds. Gottron papules are over the knuckles; lupus lesions spare the knuckles. Anti-Ro/SSA links subacute cutaneous lupus, neonatal lupus, and Sjögren syndrome - a favorite cross-domain question.
Rule of thumb
When a question asks for the best confirmatory test, pair the clinical pattern with the most specific antibody: anti-dsDNA and anti-Sm for systemic lupus, anti-Mi-2 for classic dermatomyositis, anti-MDA5 for amyopathic disease with lung involvement, anti-centromere for limited systemic sclerosis.