Psoriasis is a chronic disorder involving inflammation and hyperproliferation of the epidermis. It affects more than 7.5 million Americans.[1] Normally, epidermal cells are sloughed and replaced within 27 days. In psoriatic skin, the life cycle lasts as little as 4 days, with reduced cell cycle time for keratinocytes (i.e., 36 hours compared with 311 hours in normal skin). The etiology is multifactorial, involving genetic predispositions and associated T-cell dysfunction, proinflammatory cytokines, activated growth factors, and neutrophil recruitment. Psoriasis has autoimmune features, but the antigen trigger is not known. (However, see Nutrition Considerations below.)

Chronic plaque psoriasis (also known as psoriasis vulgaris) is the most common form, accounting for 80-90% of cases.[2] The remaining types include guttate, pustular, inverse, and erythrodermic psoriasis. Plaque psoriasis is marked by symmetrically distributed, thick, erythematous skin plaques and silvery scales that occur primarily on extensor surfaces, including the elbows and knees, as well as the scalp, lower back, and intertriginous areas. Nail changes are present in 50-80% of cases, and they are rarely the only sign of disease. The changes manifest as pitting, thickening, onycholysis, or unusual nail coloration, including what are described as “oil spots”.

Most cases follow a relapsing-remitting course, which may be influenced by certain medications, infection (such as Group A Streptococcus), trauma, stress, alcohol, and tobacco use.[3] The lesions can be itchy, stinging or burning, painful, and/or visually and aesthetically worrisome. In severe cases, lesions cover more than 10% of the body and can have a significant effect on self-esteem and quality of life, contributing to depression and suicidal ideation. More severe symptoms, including psoriatic arthritis, occur in 10-25% of patients, sometimes resulting in permanent joint deformity if left untreated.

Risk Factors

Psoriasis can occur at any age, although peak ages for onset are 30-39 and 50-69 years old.[4] All races are affected, but the disorder is less common in Black individuals and rare in Indigenous populations of North and South America. Other factors associated with risk are as follows:

Genetics. There is a clear, although complex, genetic predisposition. Many psoriasis patients have an affected 1st-degree relative. The most consistent association is with HLA-Cw6, which can increase the risk of disease 10-fold. HLA-B17 is associated with a severe phenotype.[5]

Medication use. Medications known to exacerbate symptoms include lithium, beta-blockers, angiotensin-converting enzyme inhibitors, antibiotics, psychotropics, and nonsteroidal anti-inflammatory drugs (NSAIDs).

Infection. Patients with human immunodeficiency virus and children with recurring infections, particularly streptococcal pharyngitis, are at increased risk.

Stress. Emotional and physiologic stress (trauma) have been linked to exacerbations, which may occur up to a month after the stressful event.

Smoking. Smoking is an independent risk factor for psoriasis, either inducing the onset of or worsening pre-existing disease.[6] Psoriatic patients who smoke also exhibit poor treatment response and reduced adherence to therapy.[7]

Obesity. Overweight and obesity increase the risk of (as much as 2-fold), exacerbate, and even influence the treatment of psoriasis.[8] Additionally, psoriasis can contribute to weight gain and obesity, as psoriatic inflammation can contribute to insulin resistance and weight gain, and psoriatic arthritis can make exercise challenging.[9] See Nutritional Considerations below.

Climate. Moderate amounts of sunlight can improve psoriasis. However, ultraviolet (UV) damage from excessive sun exposure can trigger or exacerbate the disease.

Vitamin D. Studies have implicated low vitamin D status in psoriasis severity, and supplemental vitamin D has been shown to reduce psoriasis severity.[10]

Alcohol intake (see below) and tobacco use are also important risk factors.

Diagnosis

Psoriasis is usually diagnosed by the classic appearance and location of plaques. Laboratory tests are not available to confirm or exclude the diagnosis. In equivocal cases, skin biopsy may aid diagnosis.

Psoriatic arthritis is diagnosed by history, physical examination, and exclusion of other arthritic disorders such as rheumatoid arthritis, gout, and ankylosing spondylitis. It is a seronegative arthritic disorder and may affect joints symmetrically or asymmetrically. Both peripheral and axial joints may be affected.

Treatment

Despite a wide range of therapeutic options, psoriasis can be a challenge to treat. Treatments are based on the type of psoriasis, severity, areas of skin affected, comorbidities, cost, and patient preference. Given the chronic nature of the condition, an individual’s quality of life can be significantly affected. Addressing both psychosocial and physical aspects of the disease is imperative.

Topical Therapies

Topical moisturizing creams and ointments are the initial therapy for mild to moderate localized disease and may reduce itching and scaling. Medicated shampoos, foams, or solutions are used for scalp lesions.

Topical corticosteroids are a first-line intervention and are especially useful for plaques and lesions that are resistant to other therapies. Low-potency steroids may be used on the face and intertriginous areas, whereas more potent steroids are reserved for the scalp and thick plaques on extensor surfaces. Long-term or excessive use unsupervised by a physician can lead to thinning of skin, easy bruising, and skin discoloration.

Vitamin D analogues (e.g., calcipotriene) slow keratinocyte growth, flatten lesions, and remove scales; these may be used alone or in combination with topical steroids.

Anthralin has been used effectively for more than a century. It slows proliferation of skin cells through inhibition of DNA synthesis. Use is typically limited by patient tolerance or associated skin irritation.

Tazarotene, a retinoid, slows proliferation of skin cells but may cause skin irritation and is contraindicated in women who are pregnant or who may become pregnant. Short contact therapy (20 minutes) followed by washing has been shown to be better tolerated than and as effective as traditional tazarotene therapy.[11] It may be used alone or in combination with topical steroids.

Coal tar is probably the oldest known treatment and is generally used to reduce inflammation, itching, and scaling of the scalp. It can be compounded with steroid creams or ointments and is available as a shampoo. Some preparations may also be as effective as vitamin D analogues.[12]

Topical calcineurin inhibitors (tacrolimus and pimecrolimus) are approved for the treatment of atopic dermatitis (eczema) but are not approved for psoriasis, by the Food and Drug Administration (FDA). However, these medications may be used off label for psoriasis affecting sensitive and delicate areas of the body, particularly the face and intertriginous areas, where they may be effective and allow patients to avoid chronic corticosteroid use.[13][14] While there has been no causal relationship established, the FDA issued an alert about a possible link between these medications and cases of lymphoma and skin cancer in children and adults (see Atopic Dermatitis chapter). However, a major systematic review and meta-analysis of 3.4 million people worldwide treated with topical calcineurin inhibitors found no credible increase in cancer among infants, children, and adults.[15]

Phototherapy is known to be beneficial and is used especially for moderate to severe psoriasis involving significant surface area for which topical treatment alone is impractical, when such therapy is ineffective, or when systemic side effects of oral medication are not tolerable or wish to be avoided.[16] Types of phototherapy include broad band ultraviolet B (UVB), narrow band UVB, psoralen UVA (PUVA), and laser. High-energy excimer laser treatment has been shown to be effective and safe for targeting localized psoriasis while requiring fewer office visits and sparing uninvolved skin.[17] Phototherapy may be combined with other treatments to increase efficacy. An increased risk of skin cancer may occur with some forms of phototherapy, particularly if there are additional patient-specific risk factors for skin cancer.

Systemic therapy may be required for moderate to severe, severe, or treatment-resistant psoriasis, or in patients with psoriatic arthritis. Options include oral retinoids (e.g., acitretin), apremilast, methotrexate with folic acid, azathioprine, cyclosporine, sulfasalazine, and hydroxyurea. These can have significant side effects and are contraindicated in pregnant women. Immune-modulating drugs, also known as “biologics” (e.g., infliximab, adalimumab, etanercept, secukinumab), are commonly used for psoriatic arthritis and severe and refractory cases.

Psychological approaches may be valuable in individuals with psoriasis. Stress plays an important role in the onset, exacerbation, and prolongation of psoriasis and appears to impair the clearance of lesions in phototherapy-treated patients.[18][19] Some evidence indicates that hypnosis and cognitive-behavioral stress management programs reduce symptom severity.[20][21] “Virtual communities” enable patients with psoriasis to communicate via the internet in order to support each other and have access to educational resources.[22]

NSAIDs. Psoriatic arthritis is sometimes treated with NSAIDs, which can help to lessen inflammatory symptoms, though there is some evidence that NSAIDs may exacerbate skin lesions. When NSAIDs are insufficient, disease-modifying antirheumatic drugs are necessary. Treatment options include the systemic therapies listed above, and it is typically advised that such conditions be comanaged with rheumatology.

Nutritional Considerations

Evidence indicates a strong link between diet and psoriasis. Psoriasis patients habitually consume poor diets higher in total fat, cholesterol, and refined carbohydrates, and lower in fiber, monounsaturated fat, and omega-3 fatty acids, than individuals without psoriasis.[23] Dietary strategies for treatment are aimed at eliminating inciting factors, reducing inflammation, and limiting calories. Despite numerous studies about the relationships between diet and psoriasis, the preponderance of the data suggests that changing nutritional habits alone does not replace conventional treatment but must be considered as an adjuvant.

Maintaining a healthy weight. Obesity is associated with both the development of psoriasis and the severity of this condition, along with a reduced response to systemic and biologic therapies.[9] Weight loss through either lifestyle measures or bariatric surgery, when otherwise indicated, is associated with improvement in this condition.[24] Loss of excess weight through lifestyle measures can also improve the aberrant lipid profile that is characteristic of some patients with psoriasis, as discussed below.[25]

Addressing cardiovascular risk factors through diet. Studies have found an atherogenic lipid profile in psoriasis sufferers compared with controls, with elevated levels of total and low-density lipoprotein (LDL) cholesterol and triglycerides, and low high-density lipoprotein (HDL), in addition to higher levels of both oxidized LDL (ox-LDL) and anti-ox-LDL autoantibodies. These patients also have elevations in novel cardiovascular risk factors, including C-reactive protein (CRP), homocysteine, and proinflammatory cytokines such as TNF-α.[26] Diets that address these risk factors include low-calorie and vegetarian diets and Mediterranean diets.[27][28] All of these have resulted in improvement in clinical trials with psoriasis patients.[29][30]

There are several other reasons psoriasis sufferers can benefit from a plant-based diet apart from the negative effects of animal fat on serum lipids. Plant-based diets are free of meat and eggs, which are sources of the omega-6 fat arachidonic acid. Arachidonic acid is proinflammatory and a precursor of leukotriene B4, which has a known role in aggravating psoriasis.[31] Advanced glycation end products, found chiefly in animal foods, strongly promote inflammation and oxidative stress and are found in significantly higher amounts in the blood of psoriasis patients compared with controls.[32]

Improvement of psoriasis is commonly reported following the adoption of a plant-based (vegan) diet; however, rigorous scientific investigation with controlled trials and other high-quality studies are largely absent.[33]

A gluten-free diet for select patients. A clear association between celiac disease and psoriasis has not been definitively established and remains controversial. However, a meta-analysis found a statistically significant risk of having positive IgA antigliadin antibodies (AGA) in patients with psoriasis compared with controls, and another study found that psoriasis patients have a 2.2-fold risk of being diagnosed with celiac disease compared with matched controls.[34][35] Although some clinical studies have found significant improvements in AGA-positive psoriasis patients after a gluten-free diet, other evidence showed a lack of improvement, even in patients with both psoriasis and confirmed celiac disease.[36][37] Further study of gluten-free diets for psoriasis patients is required, and current consensus recommendations are that gluten-free diets should be recommended only for those patients with documented increased serum AGA antibody levels.

Essential fatty acids and olive oil. Most clinical trials using supplemental fish oil have shown a significant benefit (as evidenced by decreases in the Psoriasis Area and Severity Index, or PASI) in patients with psoriasis.[31] Others have found that omega-3 fatty acids improve the effectiveness of standard treatments, reduce the hyperlipidemia caused by etretinate (an oral retinoid), prolong the beneficial effects of phototherapy, and reduce the nephrotoxicity of cyclosporin.[38] A 2019 pooled analysis found that omega-3 supplementation improved PASI scores, erythema, and scaling in psoriatic patients.[39]

Monounsaturated fats, particularly extra-virgin olive oil, appear to be protective in psoriasis, possibly because of the antioxidant and anti-inflammatory effects of the phytochemicals (e.g., oleocanthal) they contain. Disease progression occurs more rapidly with a low intake of monounsaturated fatty acids, and a cross-sectional study found that the intake of both fish and extra-virgin olive oil was independently predictive of both PASI scores and CRP.[22][27]

Vitamin E and selenium. Vitamin E is an antioxidant, and selenium is a cofactor for the antioxidant enzyme glutathione peroxidase. Several studies have demonstrated a low concentration of vitamin E and selenium in psoriasis patients compared with healthy individuals.[40][41] A placebo-controlled trial demonstrated significant clinical improvement in patients with erythrodermic psoriasis and psoriatic arthritis using supplementation with selenium and vitamin E, together with coenzyme Q10. Oral or topical administration of vitamin E and selenium may be beneficial in the prevention and treatment of psoriasis.

Alcohol avoidance. Alcohol consumption has been shown to increase the severity of psoriasis, and, in both men and women, alcohol overuse is associated with substandard response to treatment.[42][43] In alcohol abusers, the disease often remits with abstinence and recurs upon resumed alcohol use.[44] Even in light to moderate alcohol users, alcohol consumption is correlated with disease severity.[45]

Orders

See Basic Diet Orders chapter.

Gluten-free diet in patients with antigliadin antibodies.

Exercise.

Weight management.

Physical and occupational therapy, if indicated for psoriatic arthritis.

Smoking cessation.

Alcohol restriction, as appropriate.

Consider dermatology referral.

Screen for anxiety or depression related to disease course or treatment, and refer for psychosocial support as needed.

What to Tell the Family

The family can play an important role in improving psoriasis symptoms. Family members can encourage the patient to use medications as directed. When a therapeutic diet is prescribed, family members can help by adopting a similar diet. Doing so facilitates adherence and may also reduce the family’s health risks.

References