Psoriasis, a chronic skin condition that affects millions of people worldwide, exhibits distinct histopathological findings under the microscope. In this article, we will delve into the microscopic histopathological descriptions of the most common manifestation of psoriasis namely Chronic Plaque Psoriasis, shedding light on the key characteristics that define this condition.
Acanthosis and Rete Elongation (Psoriasiform)
When examined microscopically, psoriasis presents with regular acanthosis, often accompanied by elongated rete, a feature known as psoriasiform acanthosis, also known as "camel foot appearance" (figure 1). This alteration in skin structure is a hallmark of psoriasis.
Stratum Corneum Abnormalities
In the stratum corneum, you'll notice areas of parakeratosis, marked by mounds of neutrophils. These collections of neutrophils form what are known as Munro microabscesses, a key diagnostic feature.
Another significant feature is the presence of alternating zones of hypo and hypergranulosis in the epidermis. These changes in the granular layer contribute to the distinctive appearance of psoriatic skin.
Spongiosiform Pustules of Kogoj
Psoriasis may exhibit collections of neutrophils in the spinosum, forming spongiform pustules of Kogoj. These pustules are more commonly found in pustular psoriasis.
Suprapapillary Plate Thinning
Psoriasis is characterized by thinning of the suprapapillary plates, further contributing to the unique histological pattern observed in affected skin.
The dermis is not spared in the histopathological findings of psoriasis. It shows perivascular infiltrates, predominantly comprising lymphocytes, in the upper and middle dermal layers. Although less common, neutrophils or eosinophils may also be observed.
Dermal papillae host dilated and tortuous vessels, adding to the complexity of the psoriatic microenvironment (figure 2).
In some cases, evolving lesions may present focal spongiosis. This feature can be observed in intertriginous, acral, and scalp variants of psoriasis.
Histopathological identification of psoriasis relies on key findings: regular acanthosis, psoriasiform acanthosis, epidermal changes, Munro microabscesses, and dermal perivascular lymphocytic infiltrates.