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 only 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.)

Plaque psoriasis (also known as psoriasis vulgaris) is the most common form, accounting for 80% of cases. The remaining cases are guttate, pustular, erythrodermic, and intertriginous (flexural). 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, deformations, thickening, onycholysis, or unusual nail coloration.
Most cases follow a relapsing-remitting course, which may be influenced by certain medications, trauma, stress, alcohol, and tobacco use. The lesions can be painful and disfiguring. 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 most cases occur before 45 years of age.[2] All races are affected, but the disorder is less common in Black individuals and rare in indigenous populations of North America and South America. Other factors associated with risk follow:

Genetics. There is a clear, although complex, genetic predisposition. Nearly half of 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.[3]

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

Infection. Patients with human immunodeficiency virus (HIV) 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.

Obesity. Increasing body mass index has been associated with higher incidence of psoriasis.[4] 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. There is evidence that patients with psoriasis have lower vitamin D levels than the general population.[5]

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, and areas of skin affected.

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. However, resistance to steroid creams can develop quickly, and withdrawal may cause exacerbation of disease. Long-term or excessive use can lead to thinning of skin, easy bruising, and systemic side effects.

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.

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.[6] 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.[7]

Topical calcineurin inhibitors (tacrolimus and pimecrolimus) are not approved for psoriasis by the Food and Drug administration (FDA) and have not been proven effective for plaque psoriasis, but may be used off label for psoriasis affecting the face and intertriginous areas, where they may be effective and allow patients to avoid chronic corticosteroid use.[8],[9] While there has been no definitive 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).

Phototherapy is known to be beneficial and is used especially for moderate-to-severe psoriasis (in which more than 5-10% of body surface area is affected) or severe psoriasis. More common options include natural sunlight (lesions usually improve during the summer), UVB radiation, and psoralen plus UVA radiation (PUVA). 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.[10] Phototherapy may be combined with other treatments to increase efficacy. An increased risk of skin cancer may occur with phototherapy.

Systemic therapy may be required for moderate-to-severe, severe, or treatment-resistant psoriasis or in patients with psoriatic arthritis. Options include oral retinoids (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 (e.g., infliximab, alefacept, efalizumab, etanercept) 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.[11],[12] Some evidence indicates that hypnosis and cognitive-behavioral stress management programs reduce symptom severity.[13],[14] “Virtual communities” enable patients with psoriasis to communicate via the internet in order to support each other and have access to educational resources.[15]

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.

Nutritional Considerations

Dietary strategies are aimed at eliminating inciting factors, reducing inflammation, and limiting calories.

Maintaining a healthy weight. Obesity is associated with both the development of psoriasis and the severity of this condition, along with reduced response to systemic and biological therapies.[16] Weight loss through either lifestyle measures or bariatric surgery is associated with improvement in this condition.[15],[17] Loss of excess weight through lifestyle measures can also improve the aberrant lipid profile that is characteristic of patients with psoriasis, as discussed below.[18]

Addressing cardiovascular risk factors through diet. Most studies have found an atherogenic lipid profile in psoriasis sufferers compared with controls, with elevated levels of total and LDL cholesterol and triglycerides and low 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.[19] Diets that address these risk factors include low-calorie and vegetarian diets and Mediterranean diets.[20],[21] All of these have resulted in improvement in clinical trials with psoriasis patients.[15]

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. A lower intake of the omega-6 fat arachidonic acid (found in meat and eggs) is a precursor of leukotriene B4, which has a known role in aggravating psoriasis.[22] 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 than controls.[23],[24] Evidence indicates that 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.[25] Plant-based diets can also counteract the hypertriglyceridemia that is frequently associated with retinoid treatment for psoriasis.[20]

Improvement of psoriasis is commonly reported following the adoption of a plant-based (vegan) diet; however, controlled trials are largely absent.[26]

A gluten-free diet for select patients. 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.[27],[28] 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.[20] Further study of gluten-free diets for psoriasis patients is required.

Curcumin. An active compound found in turmeric, curcumin has anti-inflammatory, antiangiogenic, antiproliferative, and antioxidant properties that can be beneficial in the treatment of psoriasis. A double-blind randomized control trial of 63 patients demonstrated a decrease in the IL-22 immunoenzyme in psoriasis vulgaris with the use of a combination of oral curcumin and topical steroids compared with using topical steroids alone, suggesting that it can be an effective adjuvant in the treatment of psoriasis with steroids.[29] Other studies have confirmed curcumin’s efficacy in the treatment of psoriasis, especially owing to its antiproliferative and antiangiogenic properties.

Essential fatty acids and olive oil. The overwhelming majority of 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.[22] 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.[30] A 2019 pooled analysis found that omega-3 supplementation improved PASI scores, erythema, and scaling in psoriatic patients.[31]

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 were independently predictive of both PASI scores and CRP.[15],[20]

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.[32],[33] 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. In women, consuming more than 2-3 alcoholic beverages per week was significantly associated with developing psoriasis, a risk attributed mainly to beer intake.[34] In men, heavy alcohol consumption (100 g or more/day) is a risk factor for both the development and worsening of psoriasis, and in both men and women, alcohol overuse is associated with substandard response to treatment.[35] In alcohol abusers, the disease often remits with abstinence and recurs upon resumed alcohol use.[36] Even in light to moderate alcohol users, alcohol consumption is correlated with disease severity.[37]

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 dermatologist referral.

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