Editing Psoriasis (section)

==Diagnosis==
[[File:Micrograph of psoriasis vulgaris.jpg|thumb|Micrograph of psoriasis vulgaris. Confluent [[parakeratosis]], psoriasiform epidermal hyperplasia [(A), EH], hypogranulosis, and an influx of numerous neutrophils in the corneal layer [(A), arrow]. (B) Transepidermal migration of neutrophils from the dermis to the corneal layer (arrows).<ref>{{cite journal | vauthors = Giang J, Seelen MA, van Doorn MB, Rissmann R, Prens EP, Damman J | title = Complement Activation in Inflammatory Skin Diseases | journal = Frontiers in Immunology | volume = 9 | pages = 639 | year = 2018 | pmid = 29713318 | pmc = 5911619 | doi = 10.3389/fimmu.2018.00639 | doi-access = free | title-link = doi }}</ref>]]

A [[medical diagnosis|diagnosis]] of psoriasis is usually based on the appearance of the skin. Skin characteristics typical for psoriasis are scaly, [[erythema]]tous plaques, papules, or patches of skin that may be painful and itch.<ref name="Weigle2013"/> No special [[blood test]]s or diagnostic procedures are usually required to make the diagnosis.<ref name="Raychaudhuri2014"/>

The [[differential diagnosis]] of psoriasis includes dermatological conditions similar in appearance such as [[discoid eczema]], [[seborrheic eczema]], [[pityriasis rosea]] (may be confused with guttate psoriasis), [[tinea unguium|nail fungus]] (may be confused with nail psoriasis) or [[cutaneous T cell lymphoma]] (50% of individuals with this cancer are initially [[misdiagnosis|misdiagnosed]] with psoriasis).<ref name=Weller2008 /> Dermatologic manifestations of systemic illnesses such as the rash of [[secondary syphilis]] may also be confused with psoriasis.<ref name=Weller2008/>

If the clinical diagnosis is uncertain, a skin [[biopsy]] or scraping may be performed to rule out other disorders and to confirm the diagnosis. Skin from a biopsy shows clubbed [[rete pegs|epidermal projections that interdigitate with dermis]] on microscopy. [[Acanthosis|Epidermal thickening]] is another characteristic [[Histology|histologic]] finding of psoriasis lesions.<ref name="Raychaudhuri2014"/><ref name="Kunz2009">{{cite journal | vauthors = Kunz M, Ibrahim SM | title = Cytokines and cytokine profiles in human autoimmune diseases and animal models of autoimmunity | journal = Mediators of Inflammation | volume = 2009 | pages = 979258 | year = 2009 | pmid = 19884985 | pmc = 2768824 | doi = 10.1155/2009/979258 | doi-access = free | title-link = doi }}</ref> The [[stratum granulosum]] layer of the epidermis is often missing or significantly decreased in psoriatic lesions; the skin cells from the [[stratum corneum|most superficial layer of skin]] are also abnormal as they never fully mature. Unlike their mature counterparts, [[parakeratosis|these superficial cells]] keep their [[Cell nucleus|nuclei]].<ref name="Raychaudhuri2014"/> Inflammatory infiltrates can typically be seen on microscopy when examining skin tissue or joint tissue affected by psoriasis. Epidermal skin tissue affected by psoriatic inflammation often has many CD8+ T cells, while a predominance of CD4+ T cells makes up the inflammatory infiltrates of the dermal layer of skin and joints.<ref name="Raychaudhuri2014"/>

===Classification===

====Morphological====
{| class="wikitable" style = "float: right; margin-left:15px; text-align:center"
! Psoriasis Type
! ICD-10 Code
|-
| Psoriasis Vulgaris
| L40.0
|-
| [[Generalized pustular psoriasis]]
| L40.1
|-
| [[Acrodermatitis continua]]
| L40.2
|-
| [[Pustulosis palmaris et plantaris]]
| L40.3
|-
| [[Guttate psoriasis]]
| L40.4
|-
| [[Psoriatic arthritis]]
| L40.50
|-
| Psoriatic spondylitis
| L40.53
|-
| [[Inverse psoriasis]]
| L40.8
|}

Psoriasis is classified as a [[papulosquamous disorder]] and is most commonly subdivided into different categories based on histological characteristics.<ref name=Menter2008 /><ref name=Jain2012/> Variants include plaque, pustular, guttate, and flexural psoriasis. Each form has a dedicated [[ICD-10]] code.<ref>{{cite web |title=Application to Dermatology of International Classification of Disease (ICD-10) |publisher=The International League of Dermatological Societies |url=http://web.ilds.org/icd10_list.php?VIEW=1&START_CODE=L40.0&START_EXT=00 |archive-url=https://web.archive.org/web/20060709183301/http://web.ilds.org/icd10_list.php?VIEW=1&START_CODE=L40.0&START_EXT=00 |url-status=dead |archive-date=9 July 2006 }}</ref> Psoriasis can also be classified into nonpustular and [[pustule|pustular]] types.<ref name="Fitz2">{{cite book | vauthors = Freedberg IM, Fitzpatrick TB |title=Fitzpatrick's dermatology in general medicine |publisher=McGraw-Hill |year=2003 |isbn=978-0-07-138076-8 |edition=6th |page=414 }}</ref>

====Pathogenetic====
Another classification scheme considers genetic and demographic factors. Type 1 has a positive family history, starts before the age of 40, and is associated with the [[human leukocyte antigen]], [[HLA-C|''HLA-Cw6'']]. Conversely, type 2 does not show a family history, presents after age 40, and is not associated with ''HLA-Cw6''.<ref name=Kupetsky2013 /> Type 1 accounts for about 75% of persons with psoriasis.<ref>{{cite journal | vauthors = Griffiths CE, Christophers E, Barker JN, Chalmers RJ, Chimenti S, Krueger GG, Leonardi C, Menter A, Ortonne JP, Fry L | title = A classification of psoriasis vulgaris according to phenotype | journal = The British Journal of Dermatology | volume = 156 | issue = 2 | pages = 258–62 | date = February 2007 | pmid = 17223864 | doi = 10.1111/j.1365-2133.2006.07675.x | s2cid = 45917573 }}</ref>

The classification of psoriasis as an autoimmune disease has sparked considerable debate. Researchers have proposed differing descriptions of psoriasis and psoriatic arthritis; some authors have classified them as autoimmune diseases<ref name="Raychaudhuri2014"/><ref name="Prieto2013"/><ref name="Weidemann2013">{{cite journal | vauthors = Weidemann AK, Crawshaw AA, Byrne E, Young HS | title = Vascular endothelial growth factor inhibitors: investigational therapies for the treatment of psoriasis | journal = Clinical, Cosmetic and Investigational Dermatology | volume = 6 | pages = 233–44 | date = September 2013 | pmid = 24101875 | pmc = 3790838 | doi = 10.2147/CCID.S35312 | doi-access = free }}</ref> while others have classified them as distinct from autoimmune diseases and referred to them as [[immune-mediated inflammatory diseases]].<ref name=Nestle/><ref name="Han2012">{{cite journal | vauthors = Han R, Rostami-Yazdi M, Gerdes S, Mrowietz U | title = Triptolide in the treatment of psoriasis and other immune-mediated inflammatory diseases | journal = British Journal of Clinical Pharmacology | volume = 74 | issue = 3 | pages = 424–36 | date = September 2012 | pmid = 22348323 | pmc = 3477344 | doi = 10.1111/j.1365-2125.2012.04221.x }}</ref><ref name="Quatresooz">{{cite journal | vauthors = Quatresooz P, Hermanns-Lê T, Piérard GE, Humbert P, Delvenne P, Piérard-Franchimont C | title = Ustekinumab in psoriasis immunopathology with emphasis on the Th17-IL23 axis: a primer | journal = Journal of Biomedicine & Biotechnology | volume = 2012 | issue = 147413 | pages = 147413 | date = June 2012 | pmid = 22754278 | pmc = 3384985 | doi = 10.1155/2012/147413 | doi-access = free | title-link = doi }}</ref>

====Severity====
[[Image:Distribution of psoriasis severity.svg|thumb|Distribution of severity]]
No consensus exists about how to classify the severity of psoriasis. Mild psoriasis has been defined as a percentage of body surface area (BSA)≤10, a [[Psoriasis Area and Severity Index]] (PASI) score ≤10, and a [[Dermatology Life Quality Index]] (DLQI) score ≤10.<ref name="Mrowietz2011">{{cite journal | vauthors = Mrowietz U, Kragballe K, Reich K, Spuls P, Griffiths CE, Nast A, Franke J, Antoniou C, Arenberger P, Balieva F, Bylaite M, Correia O, Daudén E, Gisondi P, Iversen L, Kemény L, Lahfa M, Nijsten T, Rantanen T, Reich A, Rosenbach T, Segaert S, Smith C, Talme T, Volc-Platzer B, Yawalkar N | title = Definition of treatment goals for moderate to severe psoriasis: a European consensus | journal = Archives of Dermatological Research | volume = 303 | issue = 1 | pages = 1–10 | date = January 2011 | pmid = 20857129 | pmc = 3016217 | doi = 10.1007/s00403-010-1080-1 }}</ref> Moderate to severe psoriasis was defined by the same group as BSA >10 or PASI score >10 and a DLQI score >10.<ref name="Mrowietz2011"/>

The DLQI is a 10-question tool used to measure the impact of several dermatologic diseases on daily functioning. The DLQI score ranges from 0 (minimal impairment) to 30 (maximal impairment) and is calculated with each answer being assigned 0–3 points with higher scores indicating greater social or occupational impairment.<ref name="Mease2011">{{cite journal | vauthors = Mease PJ | title = Measures of psoriatic arthritis: Tender and Swollen Joint Assessment, Psoriasis Area and Severity Index (PASI), Nail Psoriasis Severity Index (NAPSI), Modified Nail Psoriasis Severity Index (mNAPSI), Mander/Newcastle Enthesitis Index (MEI), Leeds Enthesitis Index (LEI), Spondyloarthritis Research Consortium of Canada (SPARCC), Maastricht Ankylosing Spondylitis Enthesis Score (MASES), Leeds Dactylitis Index (LDI), Patient Global for Psoriatic Arthritis, Dermatology Life Quality Index (DLQI), Psoriatic Arthritis Quality of Life (PsAQOL), Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F), Psoriatic Arthritis Response Criteria (PsARC), Psoriatic Arthritis Joint Activity Index (PsAJAI), Disease Activity in Psoriatic Arthritis (DAPSA), and Composite Psoriatic Disease Activity Index (CPDAI) | journal = Arthritis Care & Research | volume = 63 | issue = Supplement 11 | pages = S64–85 | date = November 2011 | pmid = 22588772 | doi = 10.1002/acr.20577 }}</ref>

The PASI is the most widely used measurement tool for psoriasis. It assesses the severity of lesions and the area affected and combines these two factors into a single score from 0 (no disease) to 72 (maximal disease).<ref>{{cite journal|url=http://www.skinandaging.com/article/5394|archive-url=https://web.archive.org/web/20110302031858/http://www.skinandaging.com/article/5394|url-status=dead|archive-date=2 March 2011|title=Psoriasis Update |journal=Skin & Aging |volume=14 |issue=3|year=2006 |pages=46–50}}</ref> Nevertheless, the PASI can be too unwieldy to use outside of research settings, which has led to attempts to simplify the index for clinical use.<ref name="pmid15530297">{{cite journal | vauthors = Louden BA, Pearce DJ, Lang W, Feldman SR | title = A Simplified Psoriasis Area Severity Index (SPASI) for rating psoriasis severity in clinic patients | journal = Dermatology Online Journal | volume = 10 | issue = 2 | pages = 7 | date = October 2004 | doi = 10.5070/D318W9J736 | pmid = 15530297 }}</ref>