Diagnostic approach in dermatology

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I- Introduction:

The skin is an organ accessible for clinical examination and simple para-clinical explorations.

Observation of the skin lining, external mucous membranes and dander should be part of any clinical examination.

Dermatological semiology aims to describe the basic lesions that can be:

  • Primitives, translating the initial lesion process
  • Secondary, representing the evolution of this process.

II- Recall of the structure of the skin:

  • The skin coating has the skin and its appendories.
  • The skin is made up, from the outside to the inside, by 3 distinct zones: the epidermis, the dermis and the hypodermis.

1- Epidermis:

The epidermis is a multistrated Malpighian epithelium composed of 5 cell layers:

– the basal:

  • the deepest layer of the epidermis.
  • formed of a single base of cuboid cells resting on a basal membrane.
  • Generator layer
  • Between these basal cells intercalate the melanocytes.

The thorny layer or mucous body of malpighi:

  • thickest layer.
  • has 3 to 10 polygonal cell seating: Keratinocytes.
  • These cells gradually flatten towards the surface.

The granular:

  • 1 to 4 seats of very flattened cells poor in mitochondria.

The clear layer:

  • formed of a single base of very flattened cells.

The layer:

  • outermost layer.
  • more or less thick
  • devoid of nuclei

2- Derme:

Connective organ:

– a fundamental substance,

connective fibers

Cellular elements (fibroblasts, fibrocytes)

3- Hypodermis:

It is an adipose tissue divided into lobules by conjunctiva spans.

In the dermis and hypodermis path vascular and nerve formations

4- The annexes:

The skin contains various formations called annexes:

– the pilo-sebaceous follicle formed from the hair and sebaceous gland appended to the hair canal. (1,2,3)

– the eccrine and apocrine sweat glands. (4,5)

III- Key skin functions:

The skin, located at the edge of the body and the outside environment is predestined to allow some exchanges between these two environments and above all to ensure the protection of the internal environment against an extremely aggressive environment:

  • Mechanical protection: is provided by all layers of the skin, but mainly by the corneal layer and the union devices of Malpighian cells.
  • Protection from solar radiation: It is provided mainly by the melanocytic system whose cells develop the melanic pigment and cede it to the neighbouring keratinocytes to form at the base of the epidermis a continuous pigmented tablecloth that absorbs that absorbs some of the ultraviolet photonic energy.
  • Caloric protection: The skin is the peripheral organ of thermoregulation. It thus helps to keep the temperature of the body constant (sweating, constriction of the skin vessels…).
  • Microbial protection: thanks to surface lipid film.

These examples help to understand the importance of the skin coating for the survival of the individual.

IV- Principles of dermatological examination:

The dermatology diagnosis is based on data from the interrogation, physical examination and follow-up examinations.

In theory, there are two different clinical approaches:

  • The analog, fast approach, which makes the diagnosis from the inspection on a characteristic clinical aspect. It requires having already seen the lesion to recognize it and carries the risk of error.
  • The analytical (or "reasoned") method 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.


  • It should focus on clarifying:

Age, occupation, geographical origin

Personal and family history

The history of the disease:

  • Start mode
  • The initial look,
  • evolutionary mode (acute, chronic, by thrusts),
  • functional signs associated with dermatosis: pruritus, pain;
  • the patient's medication intakes
  • environmental factors: habitat, recreation, clothing habits, sun exposure



  • The patient, relaxed, should be examined in a properly lit area, preferably in daylight. The entire skin coating is examined.
  • Examination in Wood light (ultraviolet light with a wavelength of about 360 nm) is useful for the analysis of dyschromic lesions (vitiligo, pityriasis versicolor) and in some infectious dermatoses (e.g. ringworms).

The palpation:

  • It allows you to appreciate:

The superficial relief of a lesion (example: papule)

or its infiltration (example: nodule).

The vitro pressure:

  • Practiced with a watch glass or a glass blade. It differentiates a simple erythematous macule, due to a simple vascular congestion (which disappears at vitropression), from a purpura (which persists to vitropression).

The curettage:

  • Soft scraping with a curette analyzes the thickness and adhesion of scaly lesions.
  • It also detaches the crusts (looking for an underlying elementary lesion).


  • Made with a foam tip, it highlights:
  • a dermographica (oedematory papule caused by the friction of healthy skin: corresponds to physical hives)
  • a sign of Nikolski (bubble peeling caused by the gentle friction of healthy skin: in Lyell syndrome).


  • The purpose of the dermatological examination is to define the elementary lesion, which corresponds to the earliest lesions, ideally not modified by the various local treatments, scratching or local overinfection.
  • It is important to characterize an eruption based on three factors:




The nature of the elementary lesion (macules, papules, pustules, vesicles, bubbles…) and the morphological and tinctorial characteristics:

  • Size
  • Form
  • Surface
  • Color
  • Edges
  • Consistency

The grouping of these lesions:

These can be arranged in different ways:

  • plate: 1 to 10 cm
  • cupboard: 10 cm,
  • linear: on a straight or broken line (serpigine appearance),
  • ring finger: complete ring,
  • arciform: incomplete ring,
  • polycyclic: several confluent or concentric circles,
  • cockroach: target appearance.

The topography, distribution and extent of dermatosis.

  • Ubiquitous.
  • Localized or widespread.
  • elective dermattoses: psoriasis (elbows, knees)
  • The symmetry.
  • Some dermatoses (such as psoriasis) tend to occur on areas of traumatized skin, along a streak or scratching or a surgical scar. This phenomenon is called the Koebner phenomenon.

Functional signs:

  • The master functional sign is pruritus: location, intensity and timing of occurrence.
  • Other functional signs: burns, tension, tingling…

Differences between pruritus and pain



  • It is systematic but must be oriented according to the dermatosis in question (priority research of superficial adenopathy in case of melanoma for example).


  • In many cases, analysis of skin lesions can lead 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 in search of an infectious agent responsible:

– bacterial dermatosis

– fungal (direct examination and culture of dermatophytes or yeasts),

– parasitic (search for sarcoptes by shaving)

– or viral.

– Skinbiopsy

  • It is performed when clinical semiological analysis is insufficient to diagnose certainty.
  • It allows the histological analysis of the elemental lesion (or) from which a small fragment (a few mm in diameter) is taken after local anesthesia.
  • Two sampling techniques are possible:

The punch: is a cookie cutter with a circular cylindrical blade that allows for a "carrot" of skin; this technique is often practiced in children because the time for intervention is very short

The bistouri biopsy: is more classic; it is made according to an ellipse incision, taking a sample in the orange wedge; a secondary suture is essential here

– Allergological explorations:

  • Often necessary to prove the allergic nature of a dermatosis and especially to specify the allergen in question in order to avoid it to prevent recurrences.
  • Epicutaneous tests are indicated during particularly professional contact eczemas.
  • Photobiological tests are indicated during dermatoses by photosensitization

V- Basic lesions in dermatology:

Elemental lesions are commonly classified as primary and secondary lesions



  • Macules are only visible primitive lesions. These are dyschromic spots, without relief or infiltration.
  • They can be coloured (red macules and pigmented macules) or discolored (hypochromy and achromies).

Red macules:

  • Divided into 3 categories based on the characteristics of the vitropressure:

– Erythema: a red macule that disappears completely at vitropressure. It corresponds to a congestion of the vessels of the superficial dermis, whose pressure drives away the blood.

– Vascular macules: partially erase at vitro-pressure, they correspond to an abnormal vascular dilation by its size and permanence, and/or an excess of the number of dermal capillaries. Example: the plane angioma.

– Purpura: does not fade with vitropression. corresponds to an extravasation of red blood cells in the dermis. It is a dark red spot that does not fade at vitro-pressure and evolves in a few days depending on the hues of biligenesis (from red to blue and then to yellow).

Dyschromic macules:

Pigment macules: They are due to a build-up of pigment in the epidermis or dermis.

Melanin, the natural pigment of the epidermis

  • localized: examples: chloasma or pregnancy mask, coffee-to-milk stain
  • for example: melanodermy of Addison's disease.

Non-melanic pigment, most often metallic examples: tattoo, iron in hemochromatosis.

Achromic macules: They are due to a decrease (hypochromic macule) or an absence (achromic macule) of melanocytes of the epidermis and/or melanin secretion by them. They come in the form of a clear spot.


  • Protruding eyysy whose superficial relief is well perceived at palpation, solid (containing no liquid) and less than 1 cm in diameter. Example: flat wart, hives, secondary syphilids


  • More or less protruding, rounded or ovaly, large sizes (greater than 1 cm), solid, firm and infiltrated at palpation. Example: ninous erythema


  • Visible lesions, spontaneously or after mild scratching to the curette, and palpable. They are most often associated with erythemathe and scaly lesions. Example: pityriasis versicolor, psoriasis, etc.


  • Corned thickness wider than thick. It is a visible and palpable primitive lesion. It has dry and very adhesive lesions.


  • Relief, translucent lesions, 1 to 2 mm in diameter, containing a clear serosity, located in healthy skin (example: chickenpox) or erythematous skin (example: eczema).


  • Relief injuries larger than vesicles (5 mm to several cm) containing a liquid that may be clear, yellowish, or hemorrhagic, that flows after rupture


  • Relief or more rarely flat, variable size of white or yellowish color, containing a shady serosity or frank pus. Pustules can be:

– follicular: acumine, hair-centered, most often associated with infection of one or more pilo-sebaceous follicles (e.g. bacterial folliculitis)

– either non-follicular: fairly flat, superficial, milky white and mostly amicrobial (example: pustuous psoriasis)


  • Very superficial lesions, causing an elevation of several mm in relation to the plane of the skin. Their surface is very irregular, nippled


  • There are limited swellings that evolve into four phases: nodule, softening, fistulalization, fluid flow and healing. Example: syphilitic gum.



  • Visible lesions, secondary to the clotting of a serous exudate, hemorrhagic or purulent, which correspond to an evolutionary stage of different primitive elementary lesions: bubbles, vesicles, pustules.


  • Skin thinning. It performs a depressed cup lesion more or less deep, smooth and pearly. The surface wrinkles at tangential pressure. The underlying elements (capillaries, veins, bone relief) become abnormally visible


  • Induration and loss of skin elasticity.

'Substance Losses'

  • Depending on their depth, one can distinguish:

Erosion (or exulceration): loss of flat-bottomed surface substance, healing without scarring.

Ulceration: loss of deeper substance, reaching the dermis or even the hypodermis, with more or less regular edges, healing leaving a scar.

The ulcer is a loss of chronic substance with no tendency to heal. On the lower limbs, it is often of vascular origin.

The crack is a linear erosion or ulceration, sitting preferentially in a crease, or in the palms and plants. The pearl is a crack in the labial cracks.

The bedsores is a necrosis secondaryly ulcerated at the pressure point (supportischemia).

Canker is erosion or ulceration to the point of inoculation of a contagious infection

Skin tumours:

  • A skin tumour does not correspond to a particular elementary lesion.
  • It can in fact be represented by all kinds of primitive elementary lesions (papules, nodules, erythematous or erythemato-squamous lesions) or secondary lesions (ulcerations, scabs, scars).
  • It can be unique or multiple, benign or malignant. Examples: carcinomas, melanomas.


Many dermatoses consist of a combination of primitive or secondary elementary lesions characteristic of these conditions:

  • macules or papules are frequently flaky, causing erythemato-scaly lesions;
  • common acne is polymorphic and combines closed or open papules, pustules and microcysts (comedons) affecting seborrheic skin regions (face, chest area);
  • eczema comes in the form of erythema, edema, vesicles, excoriation, oozing, crust.

VI- Conclusion:

Dermatoses are very varied and widespread. Their diagnosis is based on a well-conducted interrogation and a good clinical examination whose critical time is a thorough and methodical inspection carried out under good conditions.

The purpose of this examination is to identify the elementary lesion whose analysis and possible confrontation with the data of paraclinical explorations (histology, immunofluorescence, etc.) will enable an accurate diagnosis to be established and to establish a adequate treatment.

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