Basic injuries and diagnostic procedure in dermatology

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The skin is the body envelope, it is in continuity with the mucous membranes covering the body's natural cavities, it is an organ that has an area of about 2 m2 in an adult, which weighs just over 3 kg, and includes 3 million cells per cm2 About

Histological reminder:

  • Skin: is a heterogeneous structure in which we find epithelial cells but also connective, muscular, vascular and nerve cells. The skin consists, from the outside to the inside, of 4 distinct areas:

Epidermis: is the top layer of the skin, which it protects against external aggressions, it measures on average 0.1 mm thick (from 0.02 mm on the face to 1-5 mm thick under the soles of the feet), it renews every 28 days, it includes 4 different cell populations: keratinocytes, melanocytes, Langerhans cells, Merkel cells. The epidermis contains no blood or lymphatic vessels but contains many free nerve endings. The epidermis is a multistrated Malpighian epithelium that is composed of 4 superimposed layers:

Basal layer (basal stratum): it is the deepest layer of the epidermis, it is formed of a single base of cubic or cylindrical cells resting on the basal membrane of the dermo-epidermic junction (keratinocytes), this layer is the germ compartment and the seat of strong mitotic activity

Melanocytes: are regularly distributed along the basal layer in varying amounts, have a starry appearance and their cytoplasmic extensions insinuate themselves between the keratinocytes. They lack an intercellular junction system with neighbouring cells. Melanin is the pigment produced by melanocytes in cytoplasmic organelles

Intermediate layer (stratum spinosum or spiny layer or Malpighi mucous body): it is the thickest layer, it has 3 to 10 bases of keratinocytes of polyedral forms, which possess in their cytoplasm precursors of keratin. These cells gradually flatten to the surface but their nuclei and organelles remain intact

Granular layer (stratum granulosum): it has 2 to 3 seats of very flattened cells, whose nuclei begin to degenerate. Many keratin grains and keratins appear in keratin filament kits.

Corneal Layer (stratum corneum): it is the outermost layer, it is made up of hexagonal cells, flattened, well ordered, like scales. Cytoplasmic nuclei and organelles have completely disappeared and the cytoplasm is filled with fibrillary kits formed from keratin filaments and keratohyaline grains. On the surface, these corneocytes are eliminated in a very orderly way: this is the physiological process of peeling

Dermo-epidermal junction: separates the epidermis from the dermis, the complexity of its structure and its functional importance make it a full-fledged one. It appears between the basal keratinocytes and the papillary dermis as a thin and homogeneous wavy line where the protrusions of the epidermis alternate in the last so-called "epidermal crests" and the protrusions of the dermis in the epidermis known as "dermal papillas". The dermo-epidermal junction presents epidermis anchoring complexes on the dermis

Derme (Latin skin): forms a well-defined barrier that gives the skin resistance to tearing and elasticity to stretching. It is a connective organ made up of connective fibers and cellular elements, it consists of a fundamental substance, elastic fibers, collagen fibers, vessels and nerve nets.

Hypodermis: Continuing the dermis to depth, the hypodermis is a loose, richly vascularized connective tissue that, depending on the nutritional conditions and regions of the skin, contains more or less adipose tissue divided into lobules by spans conjunctivas

  • Skin vascularization: the vessels are numerous and are located only in the dermis (the epidermis feeds by imbibition), arteriovenous anastomoses are very numerous
  • Skin appendies:

Sweat glands: are tiny in size, located in the thickness of the dermis or subcutaneous cell tissue, they are shaped like tubes. These are exocrine glands (which release their secretion via an excretory channel that crosses the dermis, the epidermis and comes to open outside by a sweatpo), very numerous (2 to 3 million), distributed in abundance on the forehead, the p the tip of the hands, the soles of the feet, the territories of the underarms and genitals and are intended to secrete sweat. There are two types:

Apocrine glands: these glands develop at puberty, sit only at the hairy (armpit) areas, they are always associated with a pildoseous follicle

Eccrine glands: these glands sit all over the body but mainly at the palms of the hands and the soles of the feet. The eccrine glands play a thermoregulation role (in case of fever or emotional factors), in hydroelectrolytic balance and in the elimination of waste from metabolism

Pilosebacefolls: are made up of the hair follicle to which the sebaceous glands are applied secreting a lipid product and the arvatic muscles with segmental sympathetic innervation whose contraction (under the effect of cold, fear…) triggers hair straightening (goosebumps)

Structure of the hair: the hair is a very strong and elastic flexible stem, about 0.1 mm thick, it is implanted obliquely in the scalp. At its deep part, it adheres to a small bag called a "follicle"

Hair growth: hair growth is not continuous but cyclical, so you lose 80 to 100 hairs a day a month. There are three phases:

Anagen phase: lasts on average about 1000 days but can range from 2 to 6 years in humans and is the growth phase of the hair. During the anagen stage, the rate of hair growth is rapid and reaches about half to an inch per month

Catagen phase: lasts only 3 weeks, it is the transition or regression phase of the hair, it precedes the resting stage. During the catagen stage, the hair growth cycle slows down and then stops

Telengenic phase: lasting 5 to 6 weeks, is the resting phase where the hair no longer grows but remains anchored in the follicle. It is only at the end of this phase that the hair falls


Structure: it is the dorsal skin of each finger and toe, forms a very specialized appendix. The nail has multiple functions: protection, fixed counterpress plane in tactile pulp sensitivity, fine grip, aggressive or aesthetic role.

Architecture: microscopically, the nail is described to two parts: a visible part (body of the nail or limb) and a part hidden under a skin fold (root). The moon is the whitish part of the limb, located in the vicinity of the root, it is particularly well developed at the thumbs. The skin that covers the root of the nail is called the "unguéal bulge" and its free (very keratinized) end "eponychium" or cuticle, while the area below the free edge of the nail is the "hyponychium"

Diagnostic approach in dermatology:

  • The skin responds to aggressions and diseases caused by visible and/or palpable changes called "basic lesions"
  • The identification of these lesions is based on a clinical examination which will be supplemented, if necessary, by certain additional examinations
  • The dermatological apparatus includes the skin, mucous membranes and dander (nails and hair), characterized by its extent, its accessibility to semiological analysis and paraclinical gestures (biopsy for example) and its involvement in many general ailments (mirror of internal diseases)
  • The purpose of the review is to make a diagnosis – treatment
  • In theory, there are two different clinical approaches:

Analog approach: fast, which makes the diagnosis upon inspection on a characteristic clinical aspect, it requires having already seen the lesion to recognize it and carries the risk of error

Analytical method: reasoned, is slower, it corresponds to a conventional medical approach: the collection of data (analysis) precedes diagnosis (synthesis). It is this method that will be described here

  • The dermatology diagnosis is based on interrogation, physical examination and further investigations

Interrogation: will tell the story of the disease (beginning mode: abrupt or progressive, localized or diffuse), the appearance of the initial lesion, the progression of the lesion, the evolution of the condition, functional signs (pruritus) and general signs. It should also specify the concept of prior drug intake (toxidermy, induced dermatosis), environmental factors (occupation, habitat, sun exposure) and psychological factors

Dermatological examination: based mainly on inspection, palpation and incidental on vitropression, curettage and friction…


Identification of the elemental lesion: size, shape, surface, consistency, colour

Identification of formed lesions: isolated or grouped (punctiform, lenticular, nummular, plaques, tablecloths, universalis or a figurative grouping: linear, annular, arciform, zoniform)

Identification of topography: ubiquitous or elective (discovered areas – photo-dermatosis, bastion areas – psoriasis lichen – plane…)


Prurit: master symptom, either absent or present, it is important to specify its intensity, the moment of occurrence (day, night, permanent, paroxysmal, effort, rest), the exact topography

Other: burning, cooking, pain

Examination of mucous membranes and dander

General: examination of other organs (ganglions…), general signs

Additional examinations: in many cases, analysis of skin lesions leads to a diagnosis or a diagnostic group, but sometimes paraclinical explorations are essential

Superficial microbiological samples: they can be made by scraping, puncture, swab or smear… looking for an infectious agent responsible for bacterial, fungal dermatosis (direct examination and culture of dermatophytes or yeasts), parasitic (search for sarcoptes by shaving) or viral

Skin Biopsy: It is performed when clinical semiological analysis is insufficient to diagnose certainty, it allows the histological analysis of the elementary lesions (s) from which a small fragment (a few millimetres in diameter) is taken after local anesthesia. Two sampling techniques are possible:

Punch: is a piece carry with a circular cylindrical blade that allows to obtain a skin carrot, this technique is often practiced in children because the intervention time is very reduced

Biopsy with a bistouri: is more classic, it is done according to an incision in ellipse, carrying out a sample in the orange wedge, a secondary suture is, here, essential

Allergological Explorations: often necessary to prove the allergic character of a dermatosis and especially to specify the allergen in question in order to avoid it to prevent recurrences

Epicutaneous tests: are indicated during contact eczema, especially professional

Photo-biological tests: are indicated during dermatoses by photosensitization

Key basic lesions:

  • Non-palpable injuries:

Macule: stain, lesion from a few millimetres to a few centimetres in diameter, visible but non-palpable. Matches a simple color change:

Macule erythematous:

Disappearing from vitropressure: telangiectasy, erythema

Persistent in vitropression: purpura

Dyschromic macule:

Pigmented macules: spheles (freckles)

Achromatic or whitish macules: vitiligo

▪ For erythema, is a localized or diffuse redness of the skin, fading away at vitropression, we can distinguish:

Generalized erythema:

Scarlatiniform type: bright red rash, in large continuous cupboards, without intervals of healthy skin (e.g. scarlet fever)

Morbiliform type: extended red rash, made of small elements with healthy skin intervals (e.g. measles)

Roséoliform type: erythema made of spots, poorly delineated with wide intervals of healthy skin (e.g. secondary syphilis)

Erythrodermia: generalized erythema that affects more than 90% of the body surface (e.g. erythrodermic psoriasis)

Localized erythema: e.g. photosensitivity

  • Palpable injuries:

Non-liquid content:

Papule: solid, palpable protruding eysy, of non-liquid content, with a diameter of less than 1 cm (e.g. hives)

Nodule: protruding, circumscribed, measuring more than 1 cm (e.g. nodular basal cell carcinoma)

Gum: large inflammatory dermo-hypodermic formation, passing through 4 stages: nodules – softening – ulceration – scarring (e.g. tuberb gum)

Vegetation: growths of filiform appearance, soft consistency, relief lesion, irregular surface, covered with fissurary furrows (cauliflower appearance, e.g. condylomes)

Verrucosity: vegetation whose surface is covered with a keratosic coat (e.g. wart)

Liquid content:

▪ Vesicle: lesion of a few millimetres (< 3 mm) de diamètre, en relief, à contenu liquidien clair (ex : eczéma) 3="" mm)="" de="" diamètre,="" en="" relief,="" à="" contenu="" liquidien="" clair="" (ex="" :=""></ 3 mm) de diamètre, en relief, à contenu liquidien clair (ex : eczéma)>

Bubble: Lesion measuring more than 5 mm in diameter, in relief, with clear content, disorder or haemorrhagic content (e.g. bubbles of autoimmune bubble dermatosis (pemphigus))

Pustule: circumscribed uplift of the epidermis containing pus, either follicular (centered by a hair, e.g. acne) or non-follicular (e.g. pustulous psoriasis)

  • Damage by altering the surface of the skin: normal skin is dry, smooth, it is altered when it becomes rough, scaly or absent

Exulceration (erosion): loss of surface substance, affecting exclusively the epidermis (e.g. syphilitic canker, mouth sores)

Ulceration: loss of substance affecting the dermis, followed by scarring (e.g. leg ulcer)

Croute: superficial drying of exudate, secretion, serosity or skin hemorrhage

Squames: layer strips that stand out on the surface of the skin, are not very adhering and easily detach, they are spontaneously visible or appear after scraping with a foam-edged curette. Traditionally, one distinguishes:

Scarlatiniform Squames: dander in large shreds, reflecting a brutal and intense corneal production

Squames in collar: small fine dander, adherent to the centre but not to the periphery, covering an inflammatory lesion (e.g. g. gibert's pink pityriasis)

Pityriasiform Squames: small, fine, unadenced, whitish and

floury, they are typical of pityriasis capitis (scalp films)

Ichtyosiform Dquames: large polygonal dander, such as fish scales, detaching from a very dry coat

Psoriasiform Squames: white, shiny, lamellar, wide and numerous (e.g. psoriasis)

  • Lesions by altering the consistency of the skin: the skin becomes too much or enough soup

Atrophy: thinning of the skin, whitish, pearly lesion, with depressed skin, finely slating (e.g. sclero-atrophic lichen)

Sclerosis: induration of the skin, which becomes difficult to wrinkle with the erasure of relief (e.g. scleroderma)

Note: poïkilodermia: a colourful condition, with atrophy, leukeneodermy and telangiectasy (e.g. Xeroderma Pigmentosum) on the same lesion

  • There are a few simple ways to refine the diagnosis:

Vitropression: is to apply a transparent object (glass or plastic) against the skin lesion, thus emptying it of its blood (e.g. erythema fades with vitropressure)

Wood's light exam: is to examine the skin in ultraviolet light in the dark (infectious dermatoses…)

Application of Chinese ink: allows you to search for scaly furrows

Firm linear stimulation: using a soft tip, allows you to search for a dermographic

Scraping with a foam curette (from Brocq): allows you to show the characteristic flaking of psoriasis

Dermatological magnifying glass: helps to refine the inspection

Dermatoscopy: for the examination of emersion and epi-illumination lesions, allows, after the application of a drop of oil, to carry out an inspection through the corneal layer that becomes transparent

Histological elementary lesions:

Histopathological terminology is essential for an effective anatomoclinical confrontation

  • Epidermal lesions:

Acanthose: is defined by an increase in the overall thickness of the epidermis, acanthose can be diffused or selectively affect the epidermal crests, in this case, the acanthose is called "psoriasiform". In the case of a selective increase in the thickness of the granular layer, it is called "hypergranulosis", the plane lichen is the characteristic example

Hyperkeratosis: is a thickening of the corneal layer, it can only be relative when there is a decrease in the thickness of the underlying stratum spinosum and granulosum. If keratinocytes keep their usual appearance devoid of nuclei, it is an "orthokeratosic" hyperkeratosis. "Paraatosis" is defined as a persistence of nuclei within corneocytes, it is observed mainly in diseases where epidermal renewal is accelerated

Acantholyse: is characterized by a loss of the intercellular connection of keratinocytes, the cells appear isolated from each other and this leads to the formation of intra-epidermal bubbles, as in pemphigus. This acantholyse can be seen on all levels of the epidermis

Spongiosis: results in a spread of keratinocytes from each other due to intercellular edema, intercellular spaces are clear and widened, resulting in "mesh" images

  • Dermo-epidermal alterations:

Papillomatosis: results in an exaggeration of the design of the papillae and inter-papillary crests, so it is frequently accompanied by an acanthose

  • Dermal injuries:

Dermal atrophy: is characterized by a decrease in overall thickness, scarcity of collagen and hypotrophy of the appendices

Sclerosis: on the contrary, is defined by a thickening of collagen, which becomes very horizontal

Fibrosis: refers to an increase in collagen fibers and dermal fibroblasts

  • Hypodermic lesions:

Cytostéatonecrosis (fat necrosis): results in the presence of burst fat cells that result in puddles of slightly basophilic molten fats


The architecture of the skin is complex which includes several cellular populations as well as annexes. A good clinical examination identifies the elementary lesion that is the cornerstone for diagnosis. Given the accessibility of the skin, a few additional tests can help our diagnostic process. Any semiological elementary lesion has a histological interpretation (histological elementary lesion)

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