Skin rash (skin rash)

Exanthema (rash) is a discrete pathological formation of the skin, its response to the effects of toxins and metabolites of the pathogen. The skin reaction is manifested by plethora of the vessels of the microcirculatory bed, increased vascular permeability with the development of edema and hemorrhage, necrosis of the epidermis and deeper layers of the skin, dystrophic changes in cells (balloon dystrophy), serous, purulent, serous-hemorrhagic inflammation. Depending on the prevalence and severity of these processes, one or another type of exanthema is formed. The presence of a rash is important for diagnosis, and in some cases, for assessing the severity of the disease and its prognosis.

In establishing a diagnosis of skin and venereal diseases, knowledge of the morphological elements of skin rashes that appear on the skin and mucous membranes is of great importance.

A distinction is made between primary morphological elements, which develop as a direct result of a pathological process in the skin and mucous membranes and arise against an unchanged background, and secondary elements, which appear as a result of the evolution of primary elements on their surface or arise after their disappearance.

Primary morphological elements include: spot, blister, nodule, knot, tubercle, vesicle, bubble, pustule. Secondary morphological elements include: secondary hypo- and hyperpigmentation (secondary dyschromia), scales, crusts, cracks, erosions, ulcers, scars, vegetation, lichinification, excoriations. These rash elements are compared to the letters of the alphabet, which form words and phrases. A. I. Kartamyshev (1963) wrote: "Just as you cannot offer a book to read to a person who does not know the letters, so you cannot demand that a doctor or student diagnose a particular skin rash if he does not understand the components that form the rash."

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Primary morphological elements

In diagnostic terms, the most important are the primary morphological elements, by the nature of which (color, shape, size, outline, consistency, etc.) it is possible to determine the nosology of dermatoses in a significant number of cases.

A spot (macula) is a limited area of skin with a changed color, without changes in its relief and consistency. The spot is at the same level with the surrounding skin. Spots can be vascular, pigmented, and artificial. The causes of spots are hypopigmentation or depigmentation (for example, vitiligo) and hyperpigmentation - accumulation of melanin (for example, a "café au lait" spot in neurofibromatosis, a Mongolian spot, or hemosidirin), abnormalities in the development of skin vessels (for example, capillary hemangioma), and temporary dilation of capillaries. Erythema, or hyperemic, is a spot caused by temporary dilation of capillaries. The size of spots ranges from 1 to 5 cm or more in diameter. An erythematous spot up to 1 cm in diameter is called roseola (for example, syphilitic roseola). With diascopy, the hyperemic spot disappears. Spots formed by the release of red blood cells beyond the vessels are called hemorrhagic. Small hemorrhagic spots are called petechiae, large ones - ecchymoses. Artificial spots (tattoo, permanent makeup) appear as a result of the deposition of insoluble coloring substances in the skin.

A papule is a primary non-striated superficial morphological element characterized by a change in skin color, consistency, and resolution without scar formation. Papules usually protrude above the surface of the surrounding skin and can be palpated. Papules can be formed as a result of deposition of exogenous substances or metabolic products, cellular infiltration, or local hyperplasia. The surface of a papule can be smooth (e.g., lichen planus) or covered with scales (e.g., psoriasis). Nodules can be inflammatory or non-inflammatory. Papules formed as a result of keratinocyte or melanocyte proliferation are clearly demarcated from the surrounding skin. Deeper papules formed by cellular infiltrate have blurred boundaries. In a number of dermatoses, peripheral growth of papules or their fusion and formation of larger elements - plaques - occurs (e.g., mycosis fungoides). Plaque - a flattened formation, raised above the skin level and occupying a relatively large area. As a rule, plaques have clear boundaries.

A tubercle (tuberculum) is a primary non-striped formation that occurs as a result of the development of a granulomatous infiltrate (granuloma) in the dermis. Clinically, it is quite similar to papules. The tubercle has clear boundaries and rises above the level of the surrounding skin. The diameter of the tubercles is from 5 mm to 2-3 cm, the color is from pinkish-red to yellow-red, copper-red, bronze, cyanotic. During diascopy, the color of the tubercles may change (tuberculous tubercles). The tubercles have a dense or doughy consistency. They occur on limited areas of the skin and tend to group (e.g., syphilis) or merge (e.g., tuberculosis). Unlike nodules, a scar remains at the site of the tubercles (in the case of its disintegration - with the formation of an ulcer) or cicatricial atrophy (with the resorption of the tuberculous infiltrate). The tubercles consist of epithelioid and lymphoid cells with an admixture of giant cells, i.e. tuberculoid structure, which is of great importance in diagnosing diseases such as tuberculosis, syphilis, leprosy, etc.

A node is a primary, non-striated, round or oval infiltrative formation located in the deep dermis or subcutaneous tissue. A node differs from a papule in its larger size (2 to 10 cm or more in diameter) and depth. Nodes can be mobile or fused to the skin, and may arise as a result of limited non-specific inflammation (e.g., erythema nodosum), specific inflammatory reactions (e.g., tuberculosis of the skin), or a tumor process (e.g., dermatofibroma). Nodes have a soft or dense consistency. A histological node can be represented by the deposition of metabolic products in the dermis or subcutaneous tissue.

A vesicle (vesicula) is a primary cavity formation containing serous or serous-hemorrhagic fluid and rising above the skin level in the form of a hemispherical or round outline of an element 1.5-5 mm in size. A vesicle has a wall, a cavity and a bottom. The walls of the vesicle are so thin that the contents - plasma, lymph, blood or extracellular fluid - shine through the peak. Vesicles are formed by stratification of the epidermis (intraepidermal cavity) or by exfoliation of the epidermis from the dermis (subepidermal cavity). Exfoliation of the stratum corneum of the epidermis leads to the formation of subcorneal vesicles. This occurs, for example, in impetigo and subcorneal pustular dermatosis. The immediate cause of the formation of intraepidermal cavities is intercellular edema or spongiosis. Spongiosis is observed in delayed-type allergic reactions (for example, allergic contact dermatitis) and dyshidrotic eczema. The contents of the blister quickly dry out, turning into a crust. If the blister wall is damaged, erosion occurs.

A blister (bulla) is a primary limited cystic formation with a diameter of 0.5-0.7 cm or more, consisting of a bottom, a cap, and a cavity. The blister contains fluid and protrudes above the skin; it has sharp borders and a round or oval outline. Often, blisters are single-chambered. When several blisters or large blisters merge (for example, with dyshidrosis, bullous epidermophytosis), multi-chamber blisters may form. The contents of the blisters can be serous, bloody, or purulent. The cap can be dense, tense (for example, with herpetiform dermatitis) or flabby (for example, with pemphigus vulgaris). Blisters can be located on an inflammatory base (for example, with Duhring's herpetiform dermatitis) or on outwardly unchanged skin (for example, with pemphigus vulgaris). The cavity of the blister is located intraepidermally (for example, in common or foliaceous pemphigus, subcorneal pustulosis) or subepidermally (for example, in Lever's pemphigoid, Duhring's dermatitis herpetiformis). When the blister cap is destroyed, an erosion is formed, along the edges of which there are fragments of the blister cap. Sometimes the contents of the blister dry up into a crust, after the rejection of which no traces remain. Subepidermally located blisters leave scars after resolution (for example, in dystrophic bullous epidermolysis, bullous porphyria, etc.).

A pustule is a primary strip morphological element containing purulent or purulent-hemorrhagic exudate. Purulent exudate may be white, yellow, or yellow-green. A pustule develops around hair follicles (usually staphylococcal) or on smooth skin (usually streptococcal). The size and shape of pustules vary. A pustule confined to a hair follicle is called folliculitis. It has a conical shape and is usually pierced by a hair in the center. A superficial pustule, the contents of which quickly dry into a crust, is called phlycteia (for example, with impetigo). Superficial pustules leave temporary de- or hyperpigmentation after healing, and deep ones leave scars.

A blister (urtica) is a primary non-striped morphological element (papule or plaque) with a flat surface that occurs with edema of the upper sections of the papillary layer of the dermis. The pathognomonic sign of a blister is its ephemerality: they usually exist for no longer than a few hours and are accompanied by itching and burning. Blisters can have a smooth surface, round, annular or irregular shape. Due to the movement of edema of the dermis, the shape and size of the blisters quickly change. The color of the element is pale pink.

Secondary morphological elements

Dyschromia (dyschromia cutis) is a pigmentation disorder that occurs at the site of resolved primary or secondary morphological elements of the rash, corresponding to their size and outline. A distinction is made between secondary hyperpigmentation, de- and hypopigmentation. Hyperpigmentation at the site of former primary elements is formed as a result of the deposition of melanin (in melasma) and hemosiderin (in hemorrhagic spots). A decrease in the melanin content in the skin causes the development of secondary hypo- and depigmented spots (in amelanotic nevus, vitiligo). Secondary hyper- and hypopigmentation disappear without a trace.

A scale (squama) is a loosened exfoliating cell of the stratum corneum of the epidermis. As they move from the basal layer to the surface, keratinocytes lose their nuclei and other cellular organelles and turn into horny substance. Normally, in a healthy person, a complete replacement of epidermal cells - keratinocytes occurs every 27 hours. The process of exfoliation is unnoticeable. With increased proliferation of keratinocytes of the epidermis, a violation of the process of cell differentiation is observed and cells with nuclei are found in it (parakeratosis), and scales appear on the surface of the skin. Scales can be large (lamellar peeling), medium or small, like dust (mucoid peeling). They can be easily separated (for example, in psoriasis). Scales that are difficult to separate are formed, for example, in keratodermia, ichthyosis, solar keratosis. The skin becomes thick and rough, like coarse sandpaper. Sometimes the scales become impregnated with exudate and scaly crusts form.

Crusts (crusta) occur when the contents of vesicles, blisters, discharge (purulent exudate, blood or plasma) dry out from the surface of erosions and ulcers. There are serous, purulent and hemorrhagic crusts. Crusts formed by dried plasma are yellow, those formed by pus are green or yellow-green, and those formed by blood are brown or dark red. Superficial thin honey-colored crusts are characteristic of impetigo. Crusts can be thin, fragile, easily crumbling or thick, fused with the skin. If the exudate soaks all layers of the epidermis, then hard-to-separate thick crusts are formed. If there is necrosis of the underlying tissues, the element is called ecthyma. Numerous, massive, conical, purulent-hemorrhagic crusts are called rupiah.

A crack (rhagades, fissura) is a linear defect (rupture) that occurs due to loss of elasticity and infiltration of individual areas of the skin. Cracks are often accompanied by pain. A distinction is made between superficial and deep cracks. Superficial cracks develop within the epidermis and often occur with xerosis of the skin, eczema of the hands and feet, interdigital athlete's foot, infectious and yeast lesions of the corners of the mouth, etc. They quickly epithelialize and regress without a trace. Deep cracks are localized within the epidermis and dermis, often bleed with the formation of hemorrhagic crusts, are painful, regress with the formation of a scar (for example, Robinson-Fournier scars in syphilis).

Erosion is a superficial defect of the epidermis, while the dermis remains intact. Erosion occurs after the opening of cystic elements - vesicles, blisters and superficial pustules. Erosions have the same outlines and sizes as primary elements. However, they can be primary with mechanical irritation of the epidermis during scratching (for example, with senile itching), as well as due to maceration and friction of contacting surfaces of the epidermis. Sometimes erosions form on papular eruptions, especially when localized on mucous membranes (for example, papular-erosive syphilides). When erosion heals, no scar remains, but temporary hypo- or depigmentation may be observed.

An ulcer (ulcus) is a deep skin defect in which the epidermis and papillary layer of the dermis are lost. Deep ulcers involve all layers of the dermis and subcutaneous tissue. Ulcers can occur when tubercles, nodes or deep pustules are opened; this is how they differ from a wound, which is a defect in healthy tissue. Ulcers have a bottom and edges that can be soft (e.g., in tuberculosis) or dense (e.g., in skin cancer). Ulcers always heal, forming a scar.

A scar (cicatrix) occurs when ulcers, tubercles, and nodes heal. Within the scar, there are no skin appendages (hair follicles, sebaceous and sweat glands), as well as blood vessels and elastic fibers. Therefore, the scar surface is devoid of grooves characteristic of normal epidermis. The epidermis in scars is smooth, sometimes looking like tissue paper. Scars can also form without prior ulceration, the so-called dry way. Fresh scars are pink-red in color, their surface is shiny. Older scars can be hyper- or depigmented. Clinically, a distinction is made between flat scars, lying at the same level with normal skin, hypertrophic, thickened, rising above the surface of the surrounding skin (keloid scars) and atrophic, when their surface is thinned and located below the surface of normal skin. Cicatricial atrophy occurs when a deep-lying infiltrate is resorbed without damaging the integrity of the epidermis.

Vegetations (vegetationes) are characterized by the proliferation of dermal papillae, thickening of the spinous layer of the epidermis on the surface of various pathological elements: papules, inflammatory infiltrates, erosions, etc. Sometimes the surface of the vegetation can be covered with a stratum corneum. Such vegetations are grayish in color, they are dry and dense upon palpation (for example, with warts). With vegetating pemphigus, for example, the surface of the vegetation is eroded. Clinically, they are presented as soft, juicy, easily bleeding, pinkish-red villous formations covered with serous or serous-purulent discharge. Rapidly growing vegetations resemble cauliflower in appearance (for example, pointed condyloma). Vegetations often occur at the bottom of erosive-ulcerative defects.

Lichenification (lichenoficatio) is characterized by thickening and compaction of the skin, an increase in the skin pattern due to papular infiltration, which together resembles shagreen leather. Lichenification occurs as a result of constant scratching, most often in people suffering from allergic diseases. It occurs in atopic dermatitis, mycosis fungoides, and simple lichen of Vidal.

An abrasion, or excoriation (excoriatio), is a violation of the integrity of the skin as a result of mechanical damage. Often excoriations occur as a result of intense scratching with nails or other objects during intense itching (neurodermatitis, eczema, etc.). They are usually linear, strip-like or rounded. Abrasions can be superficial, leading only to a violation of the integrity of the epidermis and papillary layer (disappear without a trace), and deep, penetrating into the deep parts of the dermis (leave scars).

Excoriations may involve any primary element, most often a vesicle, pustule, or nodule. In such cases, the abrasion corresponds to the size of the element being excoriated. For example, in scabies, excoriations correspond to the shape of the vesicles. Excoriations may also be caused by pathomimia.

Primary affect

Primary affect is a specific skin lesion at the site of pathogen penetration, often with concomitant regional lymphadenitis. It occurs in infectious diseases with a transmissible or (less often) contact mechanism of pathogen transmission. The appearance of primary affect, as a rule, precedes other symptoms of the disease and serves as an important diagnostic symptom.

Enanthem is a local discrete lesion of the mucous membrane, similar to a skin rash. It has important clinical and diagnostic significance.

Criteria for classification of exanthemas

• type of rash elements: roseola, macule, erythema, papule, tubercle, nodule, urticaria, vesicle, pustule, bulla, petechiae, ecchymosis;
• sizes: small - up to 2, medium - up to 5, large - over 5 mm in diameter;
• form: correct, incorrect;
• homogeneity of the rash elements: monomorphic (all elements belong to the same type and have the same size); polymorphic (the rash elements differ sharply in shape, size, or there are elements of different types);
• localization of elements: symmetrical and asymmetrical, predominantly in one or another area of the skin;
• abundance of rash: single (up to 10 elements), scanty (elements can be counted) and abundant (multiple);
• metamorphosis of the rash: the appearance of an element, its development, often with the transition of one type of element into another, and the fading of the rash;
• time of appearance: early - 1-2, middle - 3-4 and late - after the 5th day of illness. When characterizing the rash, indicate the skin background (pale, hyperemic).

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