Which of the following is not true regarding the histopathology of psoriasis?
**Core Concept**
Psoriasis is a chronic inflammatory skin disease characterized by abnormal keratinocyte proliferation and immune-mediated inflammation. The histopathological examination of psoriatic lesions reveals distinctive features that differentiate it from other dermatological conditions.
**Why the Correct Answer is Right**
The hallmark of psoriasis is the presence of parakeratosis, which is the retention of nuclei in the stratum corneum. This is due to the accelerated differentiation and proliferation of keratinocytes in the epidermis. Additionally, psoriatic lesions exhibit thickening of the epidermis (acanthosis) and elongation of the dermal papillae. The immune response in psoriasis involves the activation of T lymphocytes, particularly CD4+ T cells, which contribute to the inflammation and keratinocyte proliferation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the other histopathological features of psoriasis include spongiosis, which is the intercellular edema between keratinocytes, and the presence of Munro's microabscesses, which are collections of neutrophils in the epidermis.
**Option B:** This option is incorrect because the increased vascularity in psoriatic lesions is a characteristic feature, which is due to the formation of new blood vessels in the dermal papillae.
**Option C:** This option is incorrect because the presence of a Grenz zone, which is a clear zone between the epidermis and the dermis, is a feature of lichen planus, not psoriasis.
**Clinical Pearl / High-Yield Fact**
Psoriasis is characterized by the "classic triad" of parakeratosis, acanthosis, and elongation of dermal papillae. This histopathological triad is essential for differentiating psoriasis from other dermatological conditions.
**Correct Answer: C.**