Stain

Sharply or blurredly defined, differently sized and shaped, non-palpable lesion, colour-contrasted to the surroundings. Spots may be acquired or congenital. They may occur primarily or secondarily as a result of another skin disease or its healing.

In Anglo-American literature, patches are further subdivided into "macule" < 1.0 cm and "patch" > 1.0 cm. In the following both terms are used synonymously. However, this distinction can be made in descriptions of findings.

• Dark spot (yellow, green, red, blue, brown, black):
  • Dye retention, melanin, haemosiderin, carotene, bile pigment or foreign substances: coal, powder, tar, bismuth, silver, gold, etc.
  • Increased vascular filling
  • Proliferated vascular system, e.g. naevus flammeus.
• Bright spot:
  • Pigmentation reduced or completely absent: pityriasis alba, leukoderm, vitiligo
  • Constricted blood vessels: e.g. in digitus mortuus, steroid skin
  • Disturbed blood vessel dynamics: e.g. naevus anaemicus.

• Dark spot (yellow, green, red, blue, brown, black):
  • Dye retention, melanin, haemosiderin, carotene, bile pigment or foreign substances: coal, powder, tar, bismuth, silver, gold, etc.
  • Increased vascular filling
  • Proliferated vascular system, e.g. naevus flammeus.
• In the case of red spots, the distinction between anaemic and non-anaemic spots is useful for differential diagnostic purposes. A non-anaemiable red spot (apart from a red tattoo) is caused by an accumulation of blood in the dermis. An anaemic stain, on the other hand, an erythema, results exclusively from a dilation of the dermal vessels.
• A dark (not red) spot presents itself as a contrast to its surroundings and can only be perceived as such. A clearly emerging lentigo maligna is easy to diagnose as a morphological pattern, because the brown-black spot appears as a striking feature in an otherwise normal environment. It is difficult to diagnose if the skin discoloration affects the whole integument. A generalised yellow colouring will be immediately recognisable in good light, as the yellow colour is a non-physiological colouring. The situation is different with the physiologically occurring colour, e.g. brown. A generalized brown spot as in Addison's disease, where a homogeneous brown discoloration of the skin is observed, will not be perceived as such morphologically. The initial ophthalmological diagnosis may initially be "healthy sun tanning". Here only the anamnestic data will continue.
• Light spot:
  • Reduced pigmentation: depigmentation, leukoderm
  • Constricted blood vessels: e.g. in digitus mortuus, steroid skin
  • Disturbed blood vessel dynamics: e.g. naevus anaemicus.
• A bright spot appears as a contrast to the surroundings. If there is a loss of pigment cells or a dysfunction of the pigment cells in the circumscribed areas of the skin, a bright spot appears in the surrounding healthy skin. If islands of unmodified healthy skin remain as "nappes claires" in a surrounding pathologically reddened skin (e.g. nappes claires in erythroderma), these islands of healthy skin are interpreted as apparently pathological bright spots although the skin is unchanged. A similar mechanism can be observed in psoriasis healed after dithranol treatment. The formerly lesional skin appears as a bright spot to the dithranol-pigmented environment. Here, too, the change takes place in the surrounding skin (brown coloration of the horny layer).
• A universal bright spot on the skin as in the various forms of albinism or in extensive vitiligo will not be perceived as a bright spot because the demarcation to normal skin is missing. Thus, even in the case of extensive vitiligo, it is not the bright spot as such that is disturbing, but the often bizarre islands of normally pigmented or repigmented skin.
• Basically, the following scenarios can be derived for a bright spot: Bright spots are either caused by a circumscribed disturbance of the blood vessel dynamics by vasoconstriction (naevus anaemicus) or by a reduction or complete absence of pigment cells (depigmented scar) or as a negative contrast in a colour-changing environment (dithranol discolouration in psoriasis treatment).
• A last possibility of a light discolouration arises with sclerotic skin changes. Superficial sclerosing of the dermis leads to a milky glass effect; existing vessels are rarefied, deeper vessels cannot shine through the sclerotic layer, so that a whitening effect occurs (e.g. lichen sclerosus et atrophicus).

1. Altmeyer P (2007) Dermatological differential diagnosis. The way to clinical diagnosis. Springer Medicine Publishing House, Heidelberg
2. Nast A, Griffiths CE, Hay R, Sterry W, Bolognia JL. The 2016 International League of Dermatological Societies' revised glossary for the description of cutaneous lesions. Br J Dermatol. 174:1351-1358.

3. Ochsendorf F et al (2017) Examination procedure and theory of efflorescence. Dermatologist 68: 229-242