Circumscribed, variably sized, polyetiologic (exogenously or endogenously triggered) solitary, sharply or indistinctly circumscribed, pale to deep red or bluish-livid, normothermic or hyperthermic or, more rarely, hypothermic, red spot that is always anemic.
An erythema differs in color, size, arrangement and presents as a contrast to the non-reddened, bright surroundings. It is only through this contrast that an erythema can be perceived as such. In a dark or in black skin, depending on the pigmentation type, an erythema is only faintly recognizable, as a darkened spot or not at all. This complicates the morphological diagnosis immensely.
A universal redness of the entire integument is called erythroderma.
Furthermore, when evaluating an erythema, various clinical aspects must be considered and diagnostically evaluated. These are in particular:
- Size: in international literature, erythema is defined in terms of size as <1.0cm. An erythema > 1.0cm is called a patch (patches).
- Dynamics (static, acutely transient, acutely persistent, chronically persistent, crescendo reaction with increasing dynamics, wave dynamics with increasingPhase, plateau phase and decrescendo phase).
- Arrangement and shape (gyrate, herpetiform, serpiginous, in Blaschko lines (in vascular hamartomas of the skin), segmental, anular reticular, random due to external triggers, e.g., in dermatitis solaris)
- Border (sharp-edged, fuzzy, scalloped, jagged, random)
- Color (dull red, bright red, deep red, blue-red-v.a. in vascular hamartomas)
- temperature (hypo-, normo-, hyperthermic)
- Consistency (as a spot - unchanged from the surrounding skin; a "palpable erythema" would mark the transition to a papule with incipient, inflammatory infiltration)
- Symptomatology (mild itching, severe itching, burning itching, pain)
- Association with metabolic diseases, pregnancy, malignant tumors, autoimmune diseases.
- Exogenous triggering: physical (cold, heat, pressure, UV rays), biochemical (exertion, water, irritants), allergic (contact allergens), bacterial or mycotic infections.
- Endogenous triggering: bacterial, viral, mycotic infections, UAW (drug reactions), food allergies.
- Association with fever and/or other general symptoms (arthralgias, intestinal symptoms, lassitude) in the setting of macular exanthema.
A distinction must be made between solitary erythema and erythema as a partial symptom of a generalized or exanthematous disease (e.g., macular drug exanthem or classic infectious macular exanthem). In English, this flaring up of an erythema is called a "flare up." This distinction can be made by visual diagnosis in most cases. It is of great importance for the further examination procedure (exclusively regional examination or whole-body examination).
Another important aspect that can be assessed by visual diagnosis is the heliotropy of an erythema, the dynamics of an erythema (acute or persistent) and the assessment of the general condition of macular exanthema.