Non-Cavitary Primary Morphologic Elements of the Skin: Classification, Clinical Manifestations

Primary morphologic elements are represented by changes in the skin and mucous membranes, which appeared as a result of various pathologic processes in the unchanged skin and mucous membranes.

Five primary sexless morphological elements are distinguished:

• Stain (macula);
• Node (papula);
• Tubercle (tuberculum);
• Node (nodus);
• Blister (urtica).

3D models of primary sexless morphological elements:

Inflammatory vascular stain

Non-inflammatory vascular spot

Hemorrhagic vascular stain

Hyperpigmented spot

Hypopigmented spot

(Macule / Patch)

A spot is a primary cell-free morphological element on the skin or mucous membranes, which is characterized by color change in a limited area. Spots are always flat and do not leave scars on the skin after disappearance.

Macule – <1 cm in diameter.

Patch – >1 cm in diameter.

Depending on the nature of the stain, there may be:

• Non-inflammatory;
• Inflammatory.

The stains are categorized by their origin into:

• Vascular;
• Hemorrhagic;
• Pigmented.

1. Inflammatory vascular stain

Vascular inflammatory spots appear as a result of dermal vascular dilation on the background of inflammatory reaction, which disappear when pressure is applied (diascopy).

The color of the spots can range from pale pink to bright red.

Spots up to 1 cm in diameter are called rozeola, 1 cm and larger are called erythema.

The outlines of the spots are usually irregular, the borders are indistinct.

These spots can occur in diseases such as syphilitic and infectious roseola, eczema, dermatitis, rosacea, and lupus erythematosus.

2. Non-inflammatory vascular spot

Vascular non-inflammatory spots result from temporary or permanent enlargement of skin vessels without an inflammatory response that do not disappear when pressure is applied (diascopy). For example: erythema of shame, hemangiomas or telangiectasias.

3. Hemorrhagic vascular stain

Vascular hemorrhagic spots – non-inflammatory spots that occur as a result of the release of blood elements from the vascular bed into the surrounding tissue at mechanical rupture of the vessel wall (trauma, bites) or an increase in its permeability (vasculitis, blood diseases).

Hemorrhagic spots up to 2 mm in diameter are called petechiae, from 2 mm to 1 cm – purpura, more than 1 cm – ecchymoses. Very large outpourings of blood into tissues are called hematomas.

When pressing, such spots do not disappear, but in the process of recovery can change color from bright red to yellow and green.

4. Hyperpigmented spot

Non-inflammatory spots associated with excessive deposition of melanin pigment are called hyperpigmented spots.

By origin, hyperpigmented spots can be congenital (nevi) and acquired, for example, when exposed to UV radiation (chloasma, freckles, lentigo), associated with the intake of various medications (toxic melanoderma) and artificial (tattoos, permanent makeup).

5. Hypopigmented spot

Non-inflammatory spots associated with partial or complete absence of melanin pigment deposition are called hypopigmented spots.

Hypopigmentation of the skin can be congenital total (albinism) and acquired localized (vitiligo).

Knot / Plaque (Papule / Plaque)

A nodule is a cell-free primary morphologic element of a skin rash, of dense-elastic consistency, protruding above the skin surface. Nodules after resolution do not leave behind scars, but may leave temporary or permanent pigmentation.

3D models of bandless primary morphological elements:

Epidermal papule

Epidermal-dermal papule

Dermal papule

Classification of nodules / plaques

By depth of location:

• Epidermal (callus, wart, molluscum contagiosum, palm hyperkeratosis);

• Epidermo-dermal (found in psoriasis, red flat fever, neurodermatitis, eczema, lupus erythematosus, Duhring’s dermatitis, leprosy);

• Dermal (papular syphilis (secondary syphilis).

Size:

• Papule– up to 1 cm in diameter;
• Plaque (Plaque) – more than 1 cm in diameter.

By origin:

• Inflammatory:
  • Proliferative processes in the epidermis:
    • Acanthosis (thickening of the spiny layer, such as in eczema);
    • Hypergranulosis (thickening of the granular layer, e.g. in red flat lice);
    • Hyperkeratosis (thickening of the stratum corneum, e.g., palm hyperkeratosis).
  • Infiltrative processes in the dermis (e.g. secondary syphilis).
• Non-inflammatory:
  • Metabolic – deposition of metabolic products (amyloid, lipids, mucin, etc.);
  • Tumor.

Form:

• Flat (epidermal, epidermal-dermal);
• Hemispherical (dermal);
• Spicy (follicular).

By color:

• Normal skin color (sebaceous gland adenoma, molluscum contagiosum);
• Purple (red flat lichen planus);
• Reddish (psoriasis, exanthema, secondary syphilis, acute prurigo);
• Brown (pigmented urticaria, histiocytosis);
• Bluish (blue nevi, Fabry disease);
• Yellow (xanthomas, histiocytosis, granulomatous dermatosis);
• Black (some types of nevi, Kaposi’s sarcoma).

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Nodule

Node is a cell-free primary morphologic element of skin rash, usually round, from 1 cm in diameter, characterized by different depth of occurrence (more often in deep layers). On palpation it feels denser than a nodule. It may ulcerate, leaving a scar.

The nodule, as an element, is most commonly seen in lipoma; it may also occur in tertiary syphilis, tuberculosis, leupra, cutaneous leishmaniasis, erythema nodosum, intradermal nevi, and cysts.

Classification of nodes by depth of occurrence:

• Dermo-epidermal;
• Dermal;
• Dermal-subdermal;
• Subdermal.