Common Terms Used in Rash Diagnosis
Primary Skin Lesions
| Lesion | Single small, diseased area | Macule | Circumscribed area of change without elevation |
| Papule | Solid raised lesion ≤1 cm | Nodule | Solid raised lesion ≥1 cm |
| Plaque | Circumscribed elevated confluence of papules ≥1 cm | Rash | An eruption on the skin; more extensive than a single lesion |
Secondary Skin Lesions
| Lesion | Single small, diseased area | Macule | Circumscribed area of change without elevation |
Common Conditions
| TEN | Toxic epidermal necrolysis | SJS | Stevens-Johnson syndrome |
| TSS | Toxic shock syndrome | SSS | Scalded skin syndrome |
| DIC | Disseminated intravascular coagulopathy | RMSF | Rocky Mountain spotted fever |
Pustule: vesicle containing purulent exudate
• Crust: dried, yellow exudate of plasma from broken vesicle, bulla
or pustule
• Fissure: linear, epidermal tear
• Erosion: focal loss of epidermis, moist and well circumscribed;
heals without a scar
• Ulcer: focal erosion of epidermis and dermis; heals with a scar
Macule: circumscribed flat area of skin, different in colour from
the surrounding tissue, < 0.5 cm in diameter • Patch: large macule > 0.5 cm in diameter
• Papule: solid, raised lesion < 0.5 cm in diameter with variable colour • Plaque: circumscribed elevation of skin > 0.5 cm in diameter and
with a distinct edge; often a confluence of papules
• Nodule: solid, raised and palpable lesion > 0.5 cm in diameter.
Similar to papule but located deeper in the dermis and
subcutaneous tissue
• Pustule: accumulation of fluid, usually yellow, within the
epidermis or dermis; diameter can vary, but usually < 1 cm
• Vesicle: raised circumscribed accumulation of clear, serous-like fluid (‘blister’) within a papule or epidermal layer; diameter
< 0.5 cm • Bulla: circumscribed, elevated, fluid-filled lesion > 0.5 cm in
diameter
• Petechiae: small red, brown or purple non-blanching macule
< 0.5 cm in diameter (‘flea bite’) • Purpura: red, brown or purple non-blanching lesion > 0.5 cm in
diameter. May be palpable or non-palpable (macule)
• Wheal (hive): circumscribed, firm, smooth elevated lesion that
changes in colour, appearance and location borders. Usually intensely itchy with central pallor and irregular borders (‘nettle rash’).
Diagrams of Skin lesions
LITFL Clinical Cases
- Sick Shocked and Sunburned [Dermatological Dilemma 001]
- Traumatic Angioedema [Immunological Discombobulation 001]
- Sulfa Drug Discombobulation [Immunological Discombobulation 002]
Dermatology Atlas:
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About Mike Cadogan
