Skin Lesions: Morphology and Description

Primary Lesions (Flat & Raised) - Spot On!

• Flat (Non-Palpable): Circumscribed skin color change.
  • Macule: <1cm. E.g., freckle, lentigo, junctional nevus.
  • Patch: >1cm (large macule). E.g., vitiligo, café-au-lait.

    ⭐ A herald patch in Pityriasis Rosea is a classic patch lesion.

• Raised (Palpable, Solid): Elevated above skin.
  • Papule: <1cm, solid. E.g., wart, lichen planus, molluscum.
  • Plaque: >1cm, solid, plateau-like (confluence of papules). E.g., psoriasis, chronic eczema.
  • Nodule: >0.5-1cm, solid, deeper in dermis/subcutis. E.g., erythema nodosum, dermatofibroma.
  • Tumor: >2cm (large nodule), solid, deep & wide. E.g., lipoma, large basal cell carcinoma.
  • Wheal: Transient, edematous, erythematous papule/plaque; evanescent & often pruritic. E.g., urticaria. (📌 Wheals are Welts)

Primary Lesions (Fluid & Follicular) - Bubble Trouble!

• Vesicle: Circumscribed, elevated, clear fluid-filled lesion, <1 cm. Ex: Varicella, Herpes zoster.
• Bulla: Large vesicle; circumscribed, elevated, clear fluid-filled, >1 cm. Ex: Bullous pemphigoid, Burns.
• Pustule: Circumscribed, elevated lesion containing visible pus (not clear fluid). Ex: Pustular psoriasis, Folliculitis.
• Cyst: Nodule; epithelial-lined cavity with liquid/semi-solid material (keratin, sebum). Ex: Epidermal inclusion cyst.
• Comedo: Hair follicle plugged with keratin & sebum.
  • Open (blackhead): Dilated orifice, oxidized plug.
  • Closed (whitehead): Constricted orifice, non-oxidized.
• Burrow: Serpiginous or linear track in epidermis by parasite. Ex: Scabies mite.

  ⭐ Burrows are pathognomonic for scabies.

• Telangiectasia: Persistent dilation of small superficial blood vessels. Fine, red lines. Ex: Rosacea, CREST.

Secondary Lesions - Skin's Story Continues

• Scale: Stratum corneum flakes (e.g., psoriasis).
• Crust: Dried exudate (serum, pus, blood); e.g., impetigo (honey-colored).
• Erosion: Epidermal loss; no scar (e.g., pemphigus).
• Ulcer: Dermis/subcutis loss; scars (e.g., stasis ulcer).
• Fissure: Linear skin crack; often painful (e.g., hand eczema).
• Atrophy: Skin thinning; shiny, fragile (e.g., senile, steroid).
• Scar: Post-injury fibrous tissue.
  • Hypertrophic: Raised, firm; within wound.
  • Atrophic: Depressed, thin; e.g., acne.
• Excoriation: Linear erosion from scratching.
• Lichenification: Thick epidermis, ↑skin lines from chronic rubbing.

  ⭐ Lichenification (thickened skin with exaggerated skin markings) is a hallmark of chronic rubbing, as seen in atopic dermatitis.

• Keloid: Scar extending beyond original wound borders. oka

Lesion Configuration & Description - Map The Marks

Arrangement: How lesions are grouped.

• Also Note Other Features:
  • Color: e.g., erythematous, violaceous, hyper/hypopigmented.
  • Shape: Overall form, e.g., round, oval, polycyclic, umbilicated.
  • Size: Measure in mm or cm.
  • Surface: e.g., smooth, rough, verrucous, scaly, crusted.
  • Consistency: e.g., soft, firm, fluctuant, indurated.
  • Borders: e.g., well-demarcated (sharp) vs. ill-defined (blurry).

⭐ Koebner phenomenon (isomorphic response): appearance of new lesions of a pre-existing dermatosis along lines of trauma. This is an exam-favourite fact!

High‑Yield Points - ⚡ Biggest Takeaways

• Macule (<1cm) & Patch (>1cm): Flat, non-palpable, color change.
• Papule (<1cm) & Plaque (>1cm): Elevated, palpable, solid lesions.
• Vesicle (<1cm) & Bulla (>1cm): Fluid-filled, circumscribed elevations.
• Pustule: Contains pus; Wheal: Transient, edematous, itchy elevation.
• Lichenification: Thickened skin with exaggerated lines from chronic rubbing.
• Erosion: Partial epidermal loss; Ulcer: Full-thickness epidermal loss, may scar.
• Scale: Flakes of stratum corneum; Crust: Dried exudate (serum, blood, pus).