Learning Objectives
Master the morphological vocabulary of dermatology to accurately describe skin lesions. Differentiate between primary lesions based on size (e.g., Macule vs. Patch) and content (e.g., Vesicle vs. Pustule), and distinguish between the depth of tissue loss in Erosion vs. Ulcer.
1. Flat and Elevated Solid Lesions
Primary skin lesions are first categorized by whether they are level with the skin or raised, and then further subdivided by their horizontal diameter.
| Term | Characteristics | Classic Examples |
|---|---|---|
| Macule | Flat; color change < 1 cm. | Freckle (ephelis), labial macule. |
| Patch | Flat; color change > 1 cm. | Vitiligo, large birthmarks. |
| Papule | Elevated solid lesion < 1 cm. | Acne, small Nevi, Neurofibroma. |
| Plaque | Elevated solid lesion > 1 cm. | Psoriasis. |
| Wheal | Transient smooth papule or plaque. | Hives (urticaria). |
2. Fluid-Filled Lesions and Surface Changes
Blisters and surface modifications provide clues to the inflammatory or infectious nature of a dermatologic condition.
| Term | Characteristics | Classic Examples |
|---|---|---|
| Vesicle | Small fluid blister < 1 cm. | Chickenpox, Shingles (Zoster). |
| Bulla | Large fluid blister > 1 cm. | Bullous pemphigoid. |
| Pustule | Vesicle containing pus. | Pustular psoriasis, folliculitis. |
| Scale | Flaking of the stratum corneum. | Eczema, Psoriasis. |
| Crust | Dry exudate. | Impetigo (“honey-colored crust”). |
3. Tissue Loss: Erosion vs. Ulcer
The distinction between these two terms is defined by the depth of the lesion relative to the basement membrane.
- Erosion: Partial or full loss of epidermis only. The basement membrane remains intact. It heals without scarring.
- Ulcer: Full epidermal loss that exposes the basement membrane and underlying structures (dermis, muscle, bone). Associated with scarring.
Activity: Descriptive Match
High-Yield Mnemonics & Tips:
- Size Cutoff: For almost all skin terms, 1 cm is the magic number (Macule/Patch, Papule/Plaque, Vesicle/Bulla).
- Plaque: Think of Psoriasis—it looks like a “plateau” of raised skin.
- Ulcer vs. Erosion: If it bleeds or involves the dermis, it’s an Ulcer.