Psoriasis: Overview and Risk Factors

Psoriasis, a chronic disorder involving hyperproliferation of the epidermis, affects more than 5 million Americans and nearly 80 million people worldwide. Normally, epidermal cells are sloughed and replaced within 27 days. In psoriatic skin, the life cycle lasts only 4 days. The etiology is multifactorial, involving genetic predispositions and associated T-cell dysfunction, pro-inflammatory cytokines, activated growth factors, and neutrophil recruitment.

Plaque psoriasis (also known as psoriasis vulgaris) is the most common form, accounting for 80% of cases. The remaining cases are guttate, pustular, and "inverse." Plaque psoriasis is marked by symmetrically distributed, thick, erythematous skin patches and silvery scales that occur primarily on extensor surfaces, including the elbows and knees, as well as the scalp and lower back. Nail changes are present in 50% to 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 medications (eg, prednisone withdrawal, lithium, antimalarials, beta-blockers, nonsteroidal anti-inflammatory drugs), 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 present between 20 and 40 years. All races are affected, but the disorder is less common in African Americans and rare in indigenous populations of North and South America. Other factors associated with risk follow:

• Genetics. There is a clear genetic predisposition. Nearly half of psoriasis patients have an affected first-degree relative. The most consistent association is with HLA-Cw6, which can increase the risk of disease 10-fold.
• Medication use. Medications known to exacerbate symptoms include lithium, antimalarial drugs, beta-blockers, angiotensin-converting enzyme (ACE) inhibitors, terbinafine, and nonsteroidal anti-inflammatory drugs (NSAIDs).
• Steroid therapy withdrawal. Abrupt ending of steroid therapy can result in the sudden worsening of psoriasis.
• 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. See Nutritional Considerations.
• Climate. Moderate amounts of sunlight can improve psoriasis. However, excessive sun exposure can trigger or exacerbate the disease.
• Alcohol intake and tobacco use are also important risk factors.