Circumscribed, > 1.0cm , polyetiologic (exogenously or endogenously triggered) solitary, sharply or indistinctly bordered, 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 as a contrast to the non-reddened, light-colored surroundings, and is also perceptible only through this contrast. In a dark skin, depending on the pigmentation type, a patch is only faintly visible or not at all. This complicates the morphological diagnosis.
Furthermore, when evaluating a solitary patch or multiple patches, various clinical aspects must be considered and diagnostically evaluated. These are in particular:
Size: in international literature, a patch is defined in terms of size as <1.0cm. A patch > 1,0cm is called a patch (patches).
Number and distribution (solitary, multiply grouped, disseminated, exanthematous, universal).
Arrangement and shape (gyrated, herpetiform, serpiginous, in Blaschko lines, segmental, anular, shooting disk- or cocard-like, polymorphous, reticular, defined by exogenous trigger, random)
Structural and functional assignment (follicular, sweat glands, sebaceous glands, contact areas, textile-covered, heliotrope, random)
Topographical assignment (versch. Body regions, field skin, groin skin, face, nose, auricle, capillitium, intertriginous)
Boundary (sharp-edged, fuzzy, scalloped, jagged, random)
Consistency (as a spot - unchanged from surrounding skin; a "palpable spot " would indicate transition to papule with incipient, inflammatory infiltration).