Differential diagnosis of psoriasis

In clinical dermatology, differential diagnosis of psoriasis – despite the rather specific morphological signs of its classical form (psoriasis vulgaris) – is of crucial importance, since there are a number of skin diseases with very similar symptoms.

Principles of differential diagnosis of psoriasis

In the classic form of psoriasis, the lesions are usually bilateral and symmetrical, which is why it is important to perform a complete skin examination – even if the patient has not noticed these lesions.

From a histological point of view, psoriasis is characterized by three main features: hyperkeratosis (due to locally limited changes in keratinocyte differentiation), infiltration (due to excessive proliferation of keratinocytes with the formation of an inflammatory infiltrate) and erythema (due to vasodilation, neovascularization and inflammation). For more information, see - Psoriasis vulgaris

Among the first signs of common psoriasis is the appearance of a nodular rash on the skin, which is red or pink in color. Such a rash is called papules - limited in area, dense nodules, on top of which there are grayish-white scales. These scales - a sign of accelerated keratinization (keratinization) of the upper layer of the skin - begin to peel off first at the very top of the thickened spot (plaque), and then from the entire surface of the rash.

It is important to take into account the stages of psoriasis, since at each of them the rash changes.

Experts note that diagnostic difficulties occur in cases of inverse psoriasis (where there is no scaling), pustular psoriasis (where sterile pustules appear and infiltration may be slight) and psoriatic erythroderma (where there are no plaques).

The differential diagnosis of psoriasis with other papulosquamous and eczematous skin diseases accompanied by hyperkeratosis is especially difficult, since their classification can cause certain nosological problems, and their etiology and pathogenesis are often unknown.

Therefore, for a correct diagnosis, dermatoscopy is often insufficient and a skin biopsy is required, providing histological information that must be correlated with clinical manifestations and any laboratory data.

Differences between eczema and psoriasis

What do dermatologists take into account when clinically diagnosing skin pathologies, and what differences between eczema and psoriasis provide grounds for making the correct diagnosis? The causes of their occurrence and symptoms. But with the etiology of eczema, like many dermatological pathologies, everything is not so simple: no one names its exact cause, and among the versions there are genetics and environmental factors.

Specific symptoms remain: localization and number of rashes, their structure (morphology) and color, duration and intensity of the process, etc.

Eczema usually manifests itself as intense pruritis (itching of the skin); swelling and redness of the skin with small blisters or raised red spots. The localization of the rash is the face, the skin in the folds of the elbows and knee joints (that is, inside the elbows and under the knees), the upper and lower extremities. Unlike psoriasis, with eczema the itching leads to attacks of uncontrollable excoriations (scratching), complicated by bleeding and secondary bacterial infections.

Other symptoms include darkening of the skin of the eyelids and extra folds of skin under the lower eyelids (Denny-Morgan folds) or on the palms.

This is not at all like the small red spots of psoriasis, which gradually expand and become covered with particles of dead cells of the stratum corneum. And when the wax-like scales are removed, blood appears.

However, without differential diagnostics it is impossible to decide whether the patient has eczema or psoriasis in the following two forms of eczema. In discoid exudative eczema (the so-called coin-shaped), which is characterized by round or oval spots (dry or wet) with clear boundaries. The spots can affect any part of the body, but the legs and buttocks are the most typical places. The pathology is chronic with relapses and outbreaks in the winter, and older people are more often affected.

And in dyshidrotic eczema, also known as dyshidrosis, with blistering rashes on the soles and palms, the differential diagnosis should exclude localized pustular psoriasis with exudative rash (in the same areas) with gradual capture of a large area of skin.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ]

Differences between neurodermatitis and psoriasis

Chronic skin pathology – neurodermatitis, or psychogenic dermatitis, or simple chronic lichen – like psoriasis, is not associated with an exogenous infection, and it is impossible to become infected with it.

By the way, due to the lack of a unified system for classifying the main skin diseases, both doctors and patients are faced with a large number of synonyms used to describe the same symptoms...

According to experts from the American Academy of Dermatology, psoriasis and neurodermatitis are diseases that are very closely related to each other, however, unlike psoriasis, allergic factors can play an additional role in the pathogenesis of neurodermatitis.

And the symptomatic differences between neurodermatitis and psoriasis are that neurodermatitis begins with pruritis and is more common in adult women. In this case, itching (most severe at night) can occur anywhere on the surface of the body, but the most typical places for the appearance of reddened itchy spots are considered to be areas of skin on the wrists and forearms, on the back of the neck, on the ankles and thighs, and they can also be in the anogenital area.

In addition to itching, neurodermatitis symptoms include skin changes in the affected area that develop due to excoriation. A raised, rough (scaly) spot of all shades of red-violet color appears as the itchy area is scratched. In the center of the affected area, the skin thickens and looks like a leathery layer of a grayish or brown shade (in dermatology, this is called lichenification). And along its edges, the skin is darker. As a rule, there is one such lesion, but there can be more.

The probability of an erroneous diagnosis is quite high, since the symptoms of neurodermatitis may be similar to those of psoriasis or herpes zoster. Differential diagnostics of psoriasis and diffuse neurodermatitis (other names: prurigo vulgaris Darier, prurigo diathesis Besnier, atopic allergic dermatosis) is also necessary - with more pronounced skin inflammation, itching and a larger area of damage.

[ 7 ], [ 8 ], [ 9 ], [ 10 ]

Other conditions similar to psoriasis

Now we should list some other diseases similar to psoriasis.

Differential diagnosis of psoriasis should be carried out with all inflammatory (fungal, viral or bacterial) skin diseases, as well as neoplastic pathologies that have a number of identical characteristics.

As oncologists note, Bowen's disease (a local form of squamous cell skin cancer) is similar to mild forms of common psoriasis with single rashes. And psoriatic erythroderma (the least common type of psoriasis, more often affecting men) can be mistaken for toxicoderma, seborrheic dermatitis, versicolor lichen, as well as a form of T-cell lymphoma or Sezary syndrome.

The diagnosis of inverse psoriasis creates problems, as it is usually localized in the armpits, groin, under the knees in the fold between the buttocks. In these cases, candidal diaper rash with pustules cannot be ruled out, but to confirm the diagnosis, smears are taken for Candida alb. And the correct diagnosis in these cases allows you to avoid mistakes in treatment, because the use of ointments with corticosteroids is contraindicated in fungal infections.

Among other diseases similar to psoriasis, dermatologists advise not to neglect lichen planus, a common inflammatory disease with an average age of manifestation of about 50 years. Typical localization of skin lesions (in the form of purple-red flat papules or plaques that itch a lot) is the flexor surfaces of the wrist and ankle, lower back, neck and genital areas. Small white grooves are visible on the surface of the papules; as in psoriasis, the Koebner phenomenon is noted. Differential diagnosis includes psoriasis, pink lichen, reactions to pharmacological agents and secondary syphilis. So to confirm the diagnosis, you need to do a skin biopsy and serological tests for syphilis.

When psoriasis affects only the scalp (which is extremely rare), it is sometimes very difficult to distinguish from seborrheic dermatitis. Unlike psoriasis, with seborrheic dermatitis, the falling off particles of keratinized skin have a clear yellowish appearance and are greasy to the touch.

Generalized pustular psoriasis is a severe form of the disease, in the differential diagnosis of which an allergic reaction to drugs should be considered (with the presence of non-follicular pustules on reddened and edematous skin of the face and in large folds of the body).

Differential diagnostics of nail psoriasis by mycological examination of the nail plates and cuticles is carried out with fungal diseases of the nails - onychomycosis and paronychia.