Circumscribed, > 1.0 cm large, polyetiological (exogenously or endogenously triggered), solitary, sharply or blurredly defined, pale to deep red or bluish-livid, also differently colored patch.
Like erythema or other patches, a patch differs in color, size, arrangement and presents itself as a contrast to the non-reddened, light-colored surroundings and is only perceptible through this contrast. In dark skin, depending on the type of pigmentation, a patch is only faintly visible or not visible at all. This makes morphological diagnosis more difficult.
Furthermore, when assessing a solitary patch or multiple patches, various clinical aspects must be taken into account and evaluated diagnostically. These are in particular:
- Size: in international literature, a patch is defined as being <1.0 cm in size. A patch > 1.0 cm is referred to as a patch.
- Number and distribution (solitary, multiple grouped, disseminated, exanthematic, universal)
- Arrangement and shape (gyrated, herpetiform, serpiginous, in Blaschko lines, segmental, anular, shooting-disc or cocard-like, polymorphic, reticular, defined by exogenous triggers, random)
- Structural and functional classification (follicular, sweat glands, sebaceous glands, contact points, textile-covered, heliotrope, random)
- Topographical assignment (various body regions, field skin body regions, field skin, inguinal skin, face, nose, auricle, capillitium, intertriginous)
- Boundary (sharp-edged, blurred, curved, jagged, random)
- Consistency (as a patch - unchanged from the surrounding skin; a "palpable patch" would indicate the transition to a plaque with incipient inflammatory or tumorous infiltration)