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Differential diagnosis of psoriasis
Last reviewed: 23.04.2024
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In clinical dermatology, differential diagnosis of psoriasis - despite the rather specific morphological features of its classical form (psoriasis vulgaris) - is crucial, because there are a number of skin diseases with very similar symptoms.
Principles of differential diagnosis of psoriasis
In the classic form of psoriasis, rashes are usually bilateral and symmetrical, which is why it is important to conduct a complete skin examination - even if the patient has not paid attention to these lesions.
From the histological point of view, psoriasis is characterized by three main features: hyperkeratosis (due to locally limited alteration of 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 details see - Vulgar psoriasis
Among the first signs of ordinary psoriasis - the appearance on the skin of a nodular rash, which has a red or pink color. Such a rash is called papules - limited in area dense knots, on top of which are scales of grayish-white color. These scales - a sign of accelerated keratinization (keratinization) of the upper layer of the skin - begin to slip off at the top of the thickened patch (plaque), and then from the entire surface of the rash.
It is important to consider the stages of psoriasis, as on each of them the rashes are modified.
Specialists note that difficulties in diagnosing occur in cases with reverse psoriasis (where there is no peeling), pustular psoriasis (where sterile pustules appear and infiltration can be expressed insignificantly) and psoriatic erythroderma (in which there are no plaques).
Especially difficult is the differential diagnosis of psoriasis with other papulosquamous and eczematous skin diseases accompanied by hyperkeratosis, since their classification can cause certain nosological problems, and their etiology and pathogenesis are often not known.
Therefore, for proper diagnosis, dermatoscopy is often inadequate and a skin biopsy is required that provides histological information that should be correlated with clinical manifestations and any laboratory data.
Differences of eczema from psoriasis
What do dermatologists take into account in the clinical diagnosis of cutaneous pathologies, and what are the differences between eczema and psoriasis that give the right diagnosis? Causes of their occurrence and symptoms. But with the etiology of eczema, like many dermatological pathologies, things are not so simple: there is no exact reason for its exact cause, and among the versions there is genetics and environmental factors.
There are specific symptoms: localization and amount of rashes, their structure (morphology) and color, duration and intensity of the process, etc.
Eczema is usually manifested by intense pruritus (skin itching); swelling and redness of the skin with small blisters or prominent red spots. Localization of rashes - a person, skin in the folds of the elbows and knee joints (that is, inside the elbows and under the knees), upper and lower extremities. Unlike psoriasis, with eczema itching leads to bouts of uncontrolled excoriation (scratching), complicated by bleeding and secondary bacterial infections.
Other symptoms include darkening of the eyelid skin and additional folds of the skin under the lower eyelids (folds of Denny-Morgan) or on the palms.
This is not at all like small red spots in psoriasis, which gradually expand and become covered with particles of dead cells of the stratum corneum. And when you remove scales similar to wax, blood appears.
However, without differential diagnosis it is not possible to decide whether the patient has eczema or psoriasis with the following two forms of eczema. In discoid exudative eczema (so-called coin-like), which is distinguished by round or oval spots (dry or wet), having clear boundaries. 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 winter, the elderly are more often ill.
And with dyshidrotic eczema, also known as dyshidrosis, with rashes in the form of vesicles on the soles and palms, a differential diagnosis should exclude localized pustular psoriasis with exudative rash (in the same areas) with a gradual capture of a large area of the skin.
[Differences in neurodermatitis from psoriasis
Chronic skin pathology - neurodermatitis, or psychogenic dermatitis, or simple chronic lichen, - like psoriasis, is not associated with exogenous infection, and it is impossible to catch it.
By the way, due to the absence of a unified system in the classification of the underlying skin diseases, both doctors and patients are faced with a large number of synonyms used to describe the same symptoms ...
According to the American Academy of Dermatology, psoriasis and neurodermatitis are diseases that are very closely related, but unlike psoriasis, allergic factors can play an additional role in the pathogenesis of neurodermatitis.
And the symptomatic difference between neurodermatitis and psoriasis is that neurodermatitis begins with pruritic and more often occurs in adult women. At the same time, the itch (the strongest at night) can occur anywhere on the surface of the body, but more characteristic spots for the appearance of reddened itchy spots are the areas of skin on the wrists and forearms, on the back of the neck, at the ankles and hips, they can also be anogenital zone.
In addition to itching, the symptoms of neurodermatitis include changes in the skin in the affected area that develop due to excoriation. The embossed rough (scaly) spot of all shades of red-violet appears as the scratching of the itchy place. In the center of the affected area, the skin thickens and looks like a leathery layer of gray or brown hue (in dermatology this is called lichenization). And on its edges the skin is darker. As a rule, there is one such center, but more often.
The probability of an erroneous diagnosis is quite high, since the symptoms of neurodermatitis may be similar to those of psoriasis or shingles. Differential diagnostics of psoriasis and diffuse neurodermatitis (other names of prurigo ordinary Daria, prurigo diathesis Bénya, atopic allergic dermatosis) are also needed - with more pronounced inflammation of the skin, itching and a larger area of damage.
Other diseases similar to psoriasis
And now you should list some other diseases similar to psoriasis.
Differential diagnosis of psoriasis should be performed with all inflammatory (fungal, viral or bacterial) skin diseases, as well as having a number of identical characteristics of neoplastic pathologies.
As oncologists note, Bowen's disease (local form of squamous cell carcinoma of the skin) resembles the mild forms of ordinary psoriasis with single rashes. A psoriatic erythrodermia (the least common form of psoriasis, which affects men more often) can be taken for both toxemia, and for seborrheic dermatitis, and for otaroid lichen, as well as for the form of T-cell lymphoma or Cesary's syndrome.
It creates problems diagnosing inverse psoriasis, since it is usually located under the armpits, in the groin, under the knees in the crease between the buttocks. In these cases, it is not possible to exclude candida diaper rash with pustules, but to confirm the diagnosis, take smears on 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 disregard red plaque - a common inflammatory disease with an average age of manifestation of about 50 years. Typical localization of skin lesions (in the form of violet-red flat papules or plaques that are strongly itchy) - wrist and ankle flexions, lower back, neck and genitalia. On the surface of the papules, small white grooves are visible; as in the case of psoriasis is noted the phenomenon of Kebner. 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 very rare), it is sometimes very difficult to distinguish it from seborrheic dermatitis. Unlike psoriasis, with seborrheic dermatitis, the falling parts of the cornified skin have a pronounced yellowness to the appearance and fatness - to the touch.
Generalized pustular psoriasis is a serious form of the disease, in the differential diagnosis of which one should consider allergic reactions to medications (with the presence of nefollikulyarnyh pustules on the reddened and swollen skin of the face and in large folds of the body).
Differential diagnosis of psoriasis of nails by mycological examination of nail plates and cuticles is carried out with fungal diseases of the nails - onychomycosis and paronychia.