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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:

II- Recall of the structure of the skin:

1- Epidermis:

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

– the basal:

The thorny layer or mucous body of malpighi:

The granular:

The clear layer:

The layer:

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:

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:


Age, occupation, geographical origin

Personal and family history

The history of the disease:



The palpation:

The superficial relief of a lesion (example: papule)

or its infiltration (example: nodule).

The vitro pressure:

The curettage:






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

The grouping of these lesions:

These can be arranged in different ways:

The topography, distribution and extent of dermatosis.

Functional signs:




– 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

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:

V- Basic lesions in dermatology:

Elemental lesions are commonly classified as primary and secondary lesions



Red macules:

– 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

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.








– 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)







'Substance Losses'

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:


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

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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