Classification of skin lesions

By Cristiano Antonino On May 26, 2023

We speak of skin lesions: skin manifestations such as spots, blisters, swellings, etc., are part of a large group of skin alterations and are commonly grouped under the name of skin lesions

The correct recognition of these alterations, detectable through an objective test, allows the doctor to distinguish the main skin diseases and to hypothesise possible underlying causes.

The language needed to describe these lesions, which may appear similar, is standardised.

Classification of skin lesions

Dermatological lesions, skin lesions or skin injuries, are generally classified into:

Primary elementary lesions or primary lesions: these are usually understood as the initial manifestations of a disease and are considered the direct expression of a pathological process affecting the skin.
Secondary primary lesions: which are nothing more than the evolution or outcome of a primary primary lesion.
The so-called ‘pathognomonic lesions’ are also added to these categories. The finding of this type of lesion allows the physician to make a certain diagnosis of a certain pathology, as this type of skin lesion is exclusive to a disease. Classic examples of a pathognomic lesion are the scabies burrow or the scutulum, typical of ringworm.

During the objective test, skin lesions are identified by taking into account important factors such as:

Colour
Size
Consistency
Shape
Mobility
Margins
Painfulness

In addition, in order to correctly frame the lesion and be able to hypothesise a diagnosis, it is important to consider

The number of lesions
The extent of the lesion on the skin surface
Their arrangement
The involvement of adnexa (such as nails, hair or hairs)
The involvement of skin folds

In addition to these parameters, it is important to understand, during the test, whether the skin has other lesions, distinct from the main one.

In the medical field, one speaks of monomorphism when only one type of lesion affects the skin, and of polymorphism if several elementary lesions coexist in a skin disease.

Let us look specifically at what primary and secondary skin lesions are and what they look like.

Primary elementary skin lesions

In the category of the most common primary elementary skin lesions are:

The macula or spot
The papule
The vesicle
The plaque
The pustule
The blister
The nodule
The pompho

Let’s see what they look like and what the characteristics of these lesions are.

Macula or spot

Maculae, also called spots, are non-palpable primitive lesions characterised by a change in skin colour.

The areas may be hyperchromic or hypopigmented in relation to the surrounding skin.

They generally have a diameter of less than 10 mm and are not depressed or raised in relation to the skin surface.

They are subdivided into:

Melanodermic spots, i.e. dark spots such as freckles, flat nevi, ephelides, chloasma, vinous angiomas or rashes resulting from rickettsia, measles or rubella infections.
Leukodermal spots, i.e. light spots such as those found in vitiligo, pityriasis alba, anaemic nevi, etc.
Haematomas and ecchymoses are also considered spots.

Papule

Papules are also primitive skin lesions but, unlike macules, they are in relief and therefore palpable.

They present with a diameter of less than 5 mm and may sometimes assume a cluster shape.

Dermatological lesions that characterise: warts, insect bites, nevi, lichen planus (a recurrent, itchy inflammatory eruption), some acne lesions, skin neoplasms and actinic or seborrhoeic keratoses can present as papules.

Vesicle

Vesicles are small, circumscribed and raised skin lesions.

They are usually clear, containing serous or serohematous fluid and less than 10 mm in diameter.

These lesions are characteristic of herpes infections, acute allergic contact dermatitis and chickenpox.

Plaque

The term ‘plaque’ refers, in the medical field, to a raised, solid skin lesion larger than 5 mm (larger than papule).

It is formed by the accumulation of inflammatory cells or tumour cells within the skin.

It may be elevated or depressed and flat or rounded in relation to the skin surface.

Sometimes the term ‘plaque’ is used in the medical field to describe a lesion resulting from the confluence of several papules.

The onset of plaques may be accompanied by more or less intense itching.

A correct analysis allows the physician to distinguish the triggering cause, which may be dermatophytosis, psoriasis, granuloma annulare and others.

Pustule

Similar to vesicles, pustules are circumscribed skin lesions in relief from the plane of the skin.

Unlike vesicles, pustules contain purulent, opalescent and turbid material.

Their appearance is frequent in bacterial infections (such as folliculitis) or certain inflammatory diseases such as pustular psoriasis.

Boil

Boils are raised, solid dermatological lesions represented by a cavity filled with a clear serous or serous-hematous fluid, usually larger than 10 mm.

There are numerous causes that lead to the appearance of boils, including:

Severe burns
Bites
Irritative contact dermatitis
Allergic contact dermatitis
Exposure to: extreme cold or excessive rubbing/friction

The appearance of blisters may also be a symptom of autoimmune diseases such as pemphigus vulgaris and bullous pemphigus.

Nodule

A nodule is a circumscribed skin lesion, usually rounded and palpable, with the characteristic of having a different consistency to the surrounding tissue.

Although it appears similar to a papule unlike the latter, it involves deeper subcutaneous tissue and exceeds 5 mm in diameter.

This formation can have an inflammatory, infectious or neoplastic origin.

The pathological nodule can sometimes be the expression of a benign or malignant tumour and occur in almost all organs.

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Solid, palpable nodules, on the other hand, may be the result of an injury or trauma and arise in tendons and muscles.

Nodules arising in the subcutaneous tissue and in the dermis include cysts, fibromas and lipomas.

Pompho

A pompho is a lesion of the dermis that usually appears as a roundish, reddish or pale-pearly, smooth skin relief of variable shape.

It is usually accompanied by itching.

The pomphi are a characteristic symptom of urticaria caused by drug hypersensitivity, insect bites or autoimmune diseases and tend to disappear within 24 hours.

Usually the most affected regions are the face, arms and trunk.

Secondary skin lesions

Secondary skin lesions represent the evolution of a primary lesion.

The most common secondary lesions include:

Scales: produced by a flaking of the stratum corneum. Depending on their size they are divided into laminar, lamellar, furfuraceous or pityriasis.
Scabs: represent the product of the reparative process of skin lesions and appear as a drying of exudate in correspondence of primary lesions such as pustules, blisters or vesicles.
Ulcers: characterised by loss of substance affecting the epidermis, dermis and sometimes also the hypodermis. There is usually little tendency for spontaneous healing. Various cutaneous neoplasms may occur with this lesion, for example basal cell carcinoma or spinocellular carcinoma or aphthous lesions of the oral cavity.
Excoriations: superficial skin wounds of a traumatic nature.
Ragadas: linear ulcerations of the skin and mucous membranes that occur as a result of a pathological reduction or loss of elasticity of the epidermis. They are painful manifestations and usually appear in the areas of the folds, nipples or labial commissures.
Erosions: losses that only affect the epidermis and occur following the rupture of vesicular-pustular lesions.
Scars: represent the final process of repair triggered by a skin insult; initially pink in colour, they tend to turn white or grey with the passage of time and become hollow; normal pigmentation and skin adnexa are missing inside the scars. They can be subdivided into: physiological, hypertrophic and keloid.

Dermatological diagnosis

Skin lesions are the morphological expression of the skin’s response to a pathogenic stimulus.

In cases where the appearance of these lesions is a cause for concern, it is essential to contact a professional and request a dermatological test.

For a correct nosological classification, the dermatologist will carefully observe the skin, analysing the type, number, location and arrangement of the lesions.

This will make it possible to hypothesise the different pathologies underlying the manifestations and to make a correct diagnosis.

Only once the pathology underlying the manifestation of the skin lesions presented by the patient has been discovered and understood will it be possible to establish, if necessary, the most suitable therapy for the case.

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