Psoriasis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Syed Hassan A. Kazmi BSc, MD [2]
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, Bowen’s disease, exanthematous pustulosis, hypertrophic lichen planus, Sneddon–Wilkinson 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 named "Tzaraat" in the Bible, though the term also included other skin conditions. At first, psoriasis, leprosy, and other inflammatory skin conditions were thought to be the same, but with the advancement of medical science, psoriasis became known to be 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, and urine, goose oil and semen, wasp droppings in sycamore milk, and soup made from vipers have all been reported as ancient treatments. 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 with multiple relapses and remissions but symptoms can be controlled by medications.
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 subphenotypes have been named according to distribution (localized vs. widespread), anatomical localization (flexural- also called 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 genetic predisposition, but no specific immunogen has been identified. 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 production of pro-inflammatory cytokines. Certain genes increase the susceptibility of developing psoriasis and 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 due to complex interactions between the genetics, immune system, and environmental factors.
Differentiating psoriasis from other diseases
Psoriasis must be differentiated from other diseases that cause erythematous, scaly rash, such as cutaneous T cell lymphoma/mycosis fungoides, pityriasis rosea, pityriasis rubra pilaris, pityriasis lichenoides chronica, nummular dermatitis, secondary syphilis, Bowen’s disease, exanthematous pustulosis, hypertrophic lichen planus, Sneddon–Wilkinson 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 500 per 100,000 cases to 4,600 per 100,000 cases annually. Psoriasis usually affects individuals of the Caucasian race. Psoriasis tends to affect Northern European and South East Asian countries.
Risk factors
The most potent risk factor in the development of psoriasis is autoimmunity. Other risk factors include genetic predisposition and environmental factors.
Screening
There is no consensus on screening for psoriasis among the general population but screening tools exist, such as the psoriasis screening tool (PST) and genetic testing.
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 with multiple relapses and remissions but symptoms can be controlled by medications.
Diagnosis
History and Symptoms
The hallmark of psoriasis is a papulosquamous, erythematous, scaly rash which can be commonly found on extensor surfaces of the body. Although flexural surfaces may also be involved in 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, long-term erythematous scaly rash with recent presentation of arthralgia/arthralgia without any visible skin findings. Other extra cutaneous symptoms include redness and tearing of eyes due to conjunctivitis or blepharitis. Avoiding of social interactions is common among patients especially during active phase.
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 level of Long Pentraxin 3 protein (PTX3) and complement levels.
X-Ray
There are no X-ray findings associated with psoriasis. However, it can be used to diagnose psoriatic arthritis which may lead to erosion of bone tissue and characteristic "pencil-in-cup" deformities. It may also lead to periostitis, dactylitis, or arthritis mutilans.
Ultrasound
There are no ultrasound findings associated with cutaneous psoriasis but ultrasound may be used as a bedside tool to visualize joints in psoriatic arthritis.
CT scan
There are no CT scan findings associated with psoriasis involving the skin but CT scan may be used to visualize the spine in psoriatic arthritis.
MRI
There are no MRI findings associated with cutaneous psoriasis but MRI may be used in 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 absent granular layer.
Treatment
Medical Therapy
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 which includes immunosupressants to counter act the disease process. The first-line treatment for symptomatic psoriatic arthritis is NSAIDs.
Surgery
Tonsillectomy may be used as a treatment for psoriasis.
Primary Prevention
There is no primary prevention for psoriasis.
Secondary Prevention
There is no secondary prevention for psoriasis.
Social Impact
The quality of life is an important factor in evaluating the severity of the disease. There are many treatments available, but because of its chronic, recurrent nature, psoriasis is challenging to treat.