Overview of CTDs - Skin's Support Woes
- Diverse group affecting skin's connective tissues (collagen, elastin, ground substance). Lead to compromised structural integrity, support, and altered skin appearance.
| Type | Pathogenesis | Common Skin Manifestations / Examples |
|---|---|---|
| Autoimmune | Immune-mediated damage to connective tissue | Photosensitivity, rash (SLE, DM); Skin thickening (Scleroderma) |
| Heritable | Genetic mutations affecting protein structure/fxn | Skin hyperextensibility, fragility (EDS); Striae, ectopia lentis (Marfan) |
⭐ Many autoimmune CTDs show interface dermatitis histologically, a key pattern to recognize.
Lupus Erythematosus - Butterfly's Sting
Autoimmune CTD; key skin manifestations:
| Type | Lesions | Systemic | Antibodies |
|---|---|---|---|
| DLE | Erythematous plaques, adherent scale, follicular plugging, atrophy, scarring | Rare | Often ANA -ve |
| SCLE | Papulosquamous/annular, photosensitive, non-scarring | ~50% mild SLE | Anti-Ro, Anti-La |
| SLE | Malar rash, photosensitivity, oral ulcers, discoid lesions (can occur) | Common | ANA, Anti-dsDNA |
⭐ Direct immunofluorescence (DIF) of lesional skin showing a 'lupus band' (granular deposits of IgG, IgM, C3 at DEJ) is highly characteristic of LE.
Scleroderma Spectrum - Hardening Truths
- Systemic Sclerosis (SSc): Autoimmune disorder; progressive skin thickening & visceral organ fibrosis.
| Feature | Limited Cutaneous SSc (lcSSc) | Diffuse Cutaneous SSc (dcSSc) |
|---|---|---|
| Skin Involvement | Fingers, hands, face/neck. Distal to elbows/knees. Slow progression. | Widespread: trunk, proximal & distal limbs. Rapid progression. |
| 📌 Mnemonic | CREST: Calcinosis, Raynaud's, Esophageal dysmotility, Sclerodactyly, Telangiectasias. | - |
| Key Antibodies | Anti-Centromere (ACA) | Anti-Scl-70 (topoisomerase I), Anti-RNA Polymerase III |
| Major Organ Risk | Pulmonary Arterial Hypertension (PAH) | Interstitial Lung Disease (ILD), Scleroderma Renal Crisis |
⭐ Anti-Scl-70 (topoisomerase I) antibodies are strongly associated with diffuse cutaneous systemic sclerosis and an increased risk of pulmonary fibrosis.
Dermatomyositis - Rash & Weakness
Autoimmune inflammatory myopathy; characteristic skin findings & proximal muscle weakness.
- Key Skin Signs:
- Heliotrope rash (eyelids)
- Gottron's papules (knuckles)
- Gottron's sign (extensor surfaces)
- Shawl sign (shoulders/back), V-sign (neck/chest)
- Mechanic's hands
- Muscle: Symmetrical proximal weakness; ↑CK, aldolase.
- Associations: Interstitial lung disease (ILD), calcinosis cutis.
- Antibodies: Anti-Mi-2 (classic), Anti-Jo-1 (ILD, mechanic's hands).
⭐ Adult-onset dermatomyositis carries a 15-25% risk of underlying internal malignancy (ovarian, lung, GI), requiring screening.
Heritable CTD Snippets - Genetic Threads
- Focus: Genetic defects primarily affecting collagen & elastin.
| Disorder | Gene(s) / Protein Defect | Key Skin Manifestations |
|---|---|---|
| Ehlers-Danlos (EDS) | COL genes; Collagen | Skin hyperextensibility, atrophic "cigarette paper" scars, easy bruising |
| Pseudoxanthoma (PXE) | ABCC6; MRP6 protein | Yellow papules ('plucked chicken skin') in flexures, lax skin |
| Marfan Syndrome | FBN1; Fibrillin-1 | Striae atrophicae (esp. shoulders, buttocks, back), thin skin |
⭐ Pseudoxanthoma elasticum (PXE), caused by ABCC6 gene mutations, classically presents with 'plucked chicken skin' appearance in flexural areas and may have serious cardiovascular and ocular (angioid streaks) complications.
High‑Yield Points - ⚡ Biggest Takeaways
- Lupus Erythematosus: Interface dermatitis, liquefaction degeneration, thickened basement membrane (PAS+), positive Lupus Band Test.
- Dermatomyositis: Heliotrope rash, Gottron's papules; interface changes; associated with internal malignancy.
- Scleroderma: Homogenized collagen, loss of adnexa; Anti-Scl-70 (diffuse), Anti-centromere (CREST).
- Morphea: Localized scleroderma with dermal sclerosis, no systemic features.
- Ehlers-Danlos Syndrome: Defective collagen causing skin hyperextensibility, joint hypermobility.
- Pseudoxanthoma Elasticum: Calcified elastic fibers; angioid streaks; ABCC6 mutation.
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