To start with lets look at normal layers of epidermis. The below posted image has been labelled and its description given below.
A = Basal cell layer (stratum basale)
B = Prickle cell layer (stratum spinosum)
C = Granular cell layer (stratum granulosum)
D = Stratum lucidum
E = Keratin layer (stratum corneum)
NOTE = The Malpighian layer of the skin is generally defined as both the stratum basale and stratum spinosum as a unit, although it is occasionally defined as the stratum basale specifically. It is named after Marcello Malpighi.
F = Superficial dermis
G = Papillary dermis
Now coming to some important terms used in dermatology.
 Orthokeratosis: This is defined as a process of normal keratinization which leads to the production of a stratum corneum composed of anucleate squames. [ Look in image above - No nucleus can be seeb in layer E - Stratum corneum]
Abnormal Pattern of keratinocyte maturation eg
 Parakeratosis : This is a process of keratinization in which the suerficial keratinocytes retain their nuclei. This is abnormal in skin but normal in mucous membrane. www.pgmeeuploads.com
See image below for example.
In the image above u can identify Nucleus ( red arrow) in stratum corneum - Parakeratosis.
Now there are condition where skin thickness is incresed it can be by increased superficial layer or increased malphigian layer.
 Acanthosis is diffuse epidermal hyperplasia (thickening of the skin). It implies increased thickness of the Malpighian layer (stratum basale and stratum spinosum).
 Hyperkeratosis is thickening of the stratum corneum (the outermost layer of the epidermis). Hyperkeratosis can be orthokeratotic were normal pattern of keratinasation leads to stratum corneum composed of anucleate squames or it can be Parakeratotic type means presence of nucleate squames in stratum corneum. www.pgmeeuploads.com
So with this background Knowlwdge we now plunge into Histopathology of Psoriasis.
HISTOPATHOLOGY OF PSORIASIS
 Hyperkeratosis with Parakeratosis - Ie thickining of stratum corneum with retention of nuclei in superficial Squames. [ See image below Label "a"]
 Hypogranulosis ie reduced layers of cells in stratum granulosum.[ See image below Label "c"]
 Acanthosis means increased thickness of the Malpighian layer (stratum basale and stratum spinosum) which is visible as elongation of rete ridges. [ See image below Label "b"] www.pgmeeuploads.com
Now as there is elongation of rete ridges so there is thickening of papillary dermis which is present in between rete ridges. At the tip of papilary dermis there are dialated capillary loops [ It leads to Auspitz’s sign, which are small bleeding points seen upon lifting of a psoriatic scale]. The epidermis over these tips is relatively thinned.
Neutrophils extravasate from these capillaries and are found in the thinned superficial epidermis (spongiform pustules of Kogoj). These neutrophils eventually aggregate in the parakeratotic layer, forming the Munro microabscess, which is characteristic of this condition.
so In epidermis we also get :-
 Spongiform pustules of Kogoj - Neutrophils in superficial dermis [ Red arrow in image below] www.pgmeeuploads.com
 Munro microabscess - Neutrophils in parakeratotic layer. See Image below
NOTE = Mitotic activity, commonly seen only in the basal cells, is typically increased in psoriasis. So that Mitotic figures are present inlayers above basal layers also.
In dermis = Superficial dermis shows a chronic inflammatory infiltrate composed mainly of small T-lymphocytes.
Now Some Important Q
Q1. Which of the following is not seen in Psoriasis www.pgmeeuploads.com
Ans =  Hypergranulosis
High Yield Point
Hypogranulosis = Psoriasis
Hypergranulosis = Lichen planus
Q2. Collections of atypical T lymphoid cells located within the epidermis are known as www.pgmeeuploads.com
 Civatte Bodies
 Pautrier's microabscess
 Munro microabscess
 Spongiform pustules of Kogoj
Ans =  Pautrier's microabscess ( Read below)
Pautrier's microabscess one of the well-defined collections of mycosis fungoides cells located within the epidermis in T-cell lymphoma (mycosis fungoides).
[*] Collection of Atypical T lymphoid cells - Mycosis fungoides cells = Pautrier's microabscess. www.pgmeeuploads.com
[*] Collection of neutrophils in epidermis in psoriasis = Munro microabscess & Spongiform pustules of Kogoj
Also Know Civatte Bodies = These bodies are generated by damaged basal keratinocytes through apoptotic cell death, consist largely of keratin intermediate filaments, and are almost invariably covered with immunoglobulins, mainly IgM. CBs have been variously termed cytoid, hyaline, colloid, or keratin bodies. It is a characteristic finding in skin lesions of patients with various dermatoses, particularly lichen planus (LP) and discoid lupus erythematosus (DLE).
Q3. Identify the skin Lesion
 Lichen Planus
 None of these
At this magnification you will be able to appreciate the elongated rete ridges (acanthosis) and parakeratosis. So this is most likely Psoriasis amomg the options provided because other 2 in option show damage to basal keratinocyte layer and rete ridges are not elongated.
HYP - Saw-tooth appearance of the epidermis is seen in Lichen Planus because of damage to basal layer and rete ridges are blunted.