Psoriasis overview

# Overview
Psoriasis is a systemic, immune-mediated disease that is characterized by inflammation of the skin and joints. It commonly causes erythematous scaly patches on the skin. The scaly patches caused by psoriasis, called psoriatic plaques, are areas of inflammation and excessive skin production. Skin rapidly accumulates at these sites and takes on a silvery-white appearance. Plaques frequently occur on the skin of the elbows and knees, but can affect any area including the scalp and genitals. Psoriasis is hypothesized to be immune-mediated and is not contagious. Psoriasis is a chronic recurring condition which varies in severity from minor localized patches to complete body coverage. Fingernails and toenails are frequently affected, which is referred to as psoriatic nail dystrophy. Psoriasis can also cause inflammation of the joints, which is known as psoriatic arthritis. 10-15% of people with psoriasis have psoriatic arthritis. The International Psoriasis Council identifies four main forms of psoriasis: plaque-type psoriasis, guttate psoriasis, generalized pustular psoriasis (GPP), and erythrodermic psoriasis. The pathophysiology of psoriasis consists of interactions between cytokines, dendritic cells, and T lymphocytes (particularly Th1 and Th17). Psoriasis must be differentiated from other diseases that cause an erythematous, scaly rash such as cutaneous T cell lymphoma/mycosis fungoides, pityriasis rosea, pityriasis rubra pilaris, pityriasis lichenoides chronica, nummular dermatitis, secondary syphilis, Bowens disease, exanthematous pustulosis, hypertrophic lichen planus, SneddonWilkinson disease, small plaque parapsoriasis, intertrigo, Langerhans cell histiocytosis, dyshidrotic dermatitis, tinea manuum/pedum/capitis, and seborrheic dermatitis. The prevalence of psoriasis is estimated to be between 500 and 4,600 cases annually per 100,000 people. The mainstay of therapy for psoriasis is topical agents applied directly onto the lesions. Topical agents include corticosteroids, vitamin D analogues, tar, anthralin, tazarotene, calcineurin inhibitors, and aloe vera extracts. Systemic therapy may also be used; this can include immunosupressants to counteract the progression of the disease.

# Historical Perspective
Psoriasis was first described during ancient times and was referred to as "Tzaraat" in the Bible, though the term also included other skin conditions. Initially, psoriasis, leprosy, and other inflammatory skin conditions were thought to be the same, but with the advancement of medical science, psoriasis became known as a separate entity. The pathophysiology of psoriasis was described in 1960s and 1970s after histopathological study of the disease. The application of cat feces to red lesions on the skin, for example, was one of the earliest topical treatments employed in ancient Egypt. Onions, sea salt, urine, goose oil and semen, wasp droppings in sycamore milk, and soup made from vipers have all been reported as ancient treatments for psoriasis. Sulfur was fashionable as a treatment for psoriasis in the Victorian and Edwardian eras and has gained importance again in the modern era as a substitute for other treatments. Psoriasis is a life-long disease that often involves multiple relapses and remissions, though symptoms can be controlled with proper medication.

# Classification
Psoriasis can be classified according to clinical appearance, morphology, and localization. The International Psoriasis Council identifies four main forms of psoriasis: plaque-type psoriasis, guttate psoriasis, generalized pustular psoriasis (GPP), and erythroderma. Psoriasis can also be classified according to disease severity into mild, moderate, and severe. Several further sub-phenotypes have been named according to distribution (localized vs. widespread), anatomical localization (flexural or inverse, scalp, palms/soles/nail), size (large vs. small) and thickness (thick vs. thin) of plaques, onset (early vs. late), and disease activity (active vs. stable).

# Pathophysiology
Psoriasis is an immune-mediated disease with a genetic predisposition, although no specific immunogen has been implicated in the development of psoriasis. The pathophysiology consists of interactions between cytokines, dendritic cells, and T lymphocytes (particularly Th1 and Th17). Common triggers of psoriasis include injury to the skin, trauma, infection, and medications. T cells play a key role in the pathogenesis of psoriasis via the production of pro-inflammatory cytokines. Certain genes increase the likelihood of developing psoriasis; the first gene that was discovered to be linked to the development of psoriasis was HLA-Cw6, which is located at PSORS1 at chromosomal position 6p21.3. Microscopically, the skin displays parakeratosis, acanthosis, hyperkeratosis, Kogoj pustules, and Munro's microabscesses. The red appearance of psoriatic lesions is due to dilated blood vessels in the skin.

# Causes
Psoriasis is caused by complex interactions between genetics, the immune system, and environmental factors.

# Differentiating psoriasis from other diseases
Psoriasis must be differentiated from other diseases that cause an erythematous, scaly rash, such as cutaneous T cell lymphoma/mycosis fungoides, pityriasis rosea, pityriasis rubra pilaris, pityriasis lichenoides chronica, nummular dermatitis, secondary syphilis, Bowens disease, exanthematous pustulosis, hypertrophic lichen planus, SneddonWilkinson disease, small plaque parapsoriasis, intertrigo, Langerhans cell histiocytosis, dyshidrotic dermatitis, tinea manuum/pedum/capitis, and seborrheic dermatitis.

# Epidemiology and demographics
The prevalence of psoriasis is estimated to be between 500 and 4,600 cases annually per 100,000 people. Psoriasis usually affects individuals of the Caucasian race. Psoriasis tends to primarily affect Northern European and Southeast Asian countries.

# Risk factors
Common risk factors in the development of psoriasis are genes which increase the susceptibility of developing psoriasis and environmental triggers. The presence of these risk factors may lead to auto-immunity and development of psoriasis.

# Screening
The national psoriasis foundation recommends screening patients affected with psoriasis for psoriatic arthritis (PsA). The CASPAR criteria may be used to screen patients for psoriastic arthritis.

# Natural history, complications and prognosis
If left untreated, patients with psoriasis may progress to develop psoriatic arthritis, joint erosions, and conjunctivitis. Common complications of psoriasis include depression, psoriatic arthritis, chronic inflammatory bowel disease, non-alcoholic fatty liver disease, celiac disease, sensorineural hearing loss, osteopenia, and osteoarthritis. Psoriasis is a life-long disease that involves multiple relapses and remissions, though symptoms can be controlled with proper medication.

# Diagnosis

## History and Symptoms
The hallmark of psoriasis is a papulosquamous, erythematous, scaly rash that can be commonly found on extensor surfaces of the body. Flexural surfaces may also be involved in cases of inverse psoriasis. Patients with psoriasis usually have a history of recent streptococcal throat infection, viral infection, immunization, use of antimalarial drugs, or trauma. The most common symptoms of psoriasis include pain, which has been described by patients as unpleasant, superficial, sensitive, itchy, hot, or burning (especially in erythrodermic psoriasis and in some cases of traumatized plaques or in the joints affected by psoriatic arthritis). Patients also present with pruritus (especially in eruptive, guttate psoriasis) and high fever in erythrodermic and pustular psoriasis. Other symptoms include dystrophic nails and long-term erythematous, scaly rash with recent presentation of arthralgia/arthralgia without any visible skin findings. Other extracutaneous symptoms include redness and tearing of eyes due to conjunctivitis or blepharitis. Avoidance of social interactions is common among patients, especially during the active phase of the disorder.

## Physical Examination
On physical examination, psoriasis is characterized by erythematous, scaling papules and plaques.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of psoriasis include increased levels of Long Pentraxin 3 protein (PTX3) and complement levels.

## X-Ray
There are no x-ray findings associated with psoriasis. However, x-rays can be used to diagnose psoriatic arthritis, which may lead to the erosion of bone tissue and characteristic "pencil-in-cup" deformities. Psoriatic arthritis may also lead to periostitis, dactylitis, or arthritis mutilans.

## Ultrasound
There are no ultrasound findings associated with cutaneous psoriasis, though ultrasound may be used as a bedside tool for the visualization of joints in cases of psoriatic arthritis.

## CT scan
There are no CT scan findings associated with psoriasis involving the skin, though a CT scan may be used to visualize the spine in cases psoriatic arthritis.

## MRI
There are no MRI findings associated with cutaneous psoriasis, though an MRI may be used in cases of psoriatic arthritis (PsA) to catch the disease in its early phase.

## Other Imaging Studies
There are no other imaging findings associated with psoriasis.

## Other Diagnostic Studies
Skin biopsy may be helpful in the diagnosis of psoriasis. Common findings include perivascular and dermal inflammatory cell infiltration, vascular dilation, and the absence of the granular layer.

# Treatment

## Medical Therapy
The mainstay of therapy for psoriasis consists of topical agents applied directly onto the lesions. Topical agents used to treat psoriasis include corticosteroids, vitamin D analogues, tar, anthralin, tazarotene, calcineurin inhibitors, and aloe vera extracts. Systemic therapy may also be used; this can include immunosupressants to counteract the progression of the disease. The first-line treatment for symptomatic psoriatic arthritis is NSAIDs.

## Surgery
Tonsillectomy may be used as a treatment for psoriasis.

## Primary Prevention
There are no established measures for the primary prevention of psoriasis.

## Secondary Prevention
There are no established measures for the secondary prevention of psoriasis.