5 Differences Between Eczema and Psoriasis
Distinguishing Between Psoriasis and Atopic Dermatitis
Two skin rashes with vastly different etiologies, prognoses, and management methods
Psoriasis and atopic dermatitis have distinct etiologies and management methods, though the differences in their clinical presentations are not always readily apparent to patients or their primary care providers. In fact, it is not uncommon for children with psoriasis to be initially misdiagnosed with atopic dermatitis.1 Both atopic dermatitis and psoriasis are non-contagious and develop due to aberrant response of the immune system to a variety of exogenous triggers. Their different etiologies result in differing disease courses and treatment approaches.
What Causes it
Both atopic dermatitis and psoriasis are systemic diseases that present with skin manifestations. Although both develop as a result of dysfunction of innate immunity, different genetic susceptibilities, cytokine abnormalities, and immune cells are responsible for their pathogeneses.
In psoriasis, chronic inflammation results in upregulation of keratinocyte production. Excess cells proliferate to reach the skin surface before they have the opportunity to mature. Normally, it takes approximately a month for skin cells to cycle thorough the phases of development, but in psoriasis, this cycle only takes a few days.2 The dead skin cells cannot be shed quickly enough to keep up with the increased turnover, and as a result, the skin becomes thickened and scaly in the affected areas.
Although the exact triggers in psoriasis are unknown, several genetic and environmental factors are thought to contribute. In addition, psoriasis is frequently associated with specific comorbid conditions:3
Genetics: Those who inherit the HLA-Cw6 gene have an increased risk of developing psoriasis. In fact, in early onset psoriasis, it was shown that 90% of patients expressed HLA-Cw6, whereas 50% of those who experience late onset have the HLA-Cw6 gene.4
Environmental Factors: Various elements in the environment can trigger the onset or exacerbate psoriasis, such as smoking, stress, trauma to the skin, infections, changes in seasons and temperatures, excessive alcohol consumption, and some medications.5
Comorbid Conditions: Because psoriasis is characterized by systemic inflammation, it is associated with other systemic pro-inflammatory conditions like cardiovascular disease, metabolic syndrome, autoimmune bullous diseases, vitiligo, alopecia areata, and Crohn’s disease.6
Patients with atopic dermatitis often have a mutation in the gene that encodes filaggrin.7 Filaggrin is a protein responsible for maintaining the protective barrier function of the epidermis.7 Without properly formed filaggrin, the skin barrier is compromised, allowing for moisture to escape, resulting in less protection from irritants, allergens, and pathogens. As a result, the skin of patients with atopic dermatitis often exist in a state of chronic inflammation, and they are more susceptible to cutaneous infections, most commonly Staphylococcus aureus.8
Additionally, those with atopic dermatitis may also experience seasonal allergies and asthma. Together, these three conditions constitute the “atopic triad.”
Who gets it
Psoriasis affects about 2-4% of the Western population.9 It can affect all ages, but is more prevalent in adults.9 Interestingly, there are two peaks for the onset of psoriasis, around 30-39 years old, and again at around 60 years old.9 Those of European descent are more likely to have psoriasis than those of Latin American, Asian, or African descent.9
Atopic dermatitis affects 1-20% of people worldwide.10 In contrast to psoriasis, atopic dermatitis is more prevalent in infants than in adults.10 In infants, African Americans are more likely to have atopic dermatitis than Hispanic, Asian, White, or Native American infants.8 In contrast, African American adults are the least likely to have atopic dermatitis compared to other races.8
Where it Shows Up
One way to tell the difference between psoriasis and atopic dermatitis is anatomic distribution. Although there are overlapping patterns, they classically appear on distinctly different areas of the body.
Psoriasis typically affects the anterior knees, extensor elbows, and torso.5 However, psoriasis can affect any part of the body, including the scalp, face, hands, nails, feet, and genitals. In 30% of patients with psoriasis, there may be joint involvement.5 Those who develop psoriatic arthritis usually require close follow up with rheumatology, as untreated psoriatic arthritis is characterized by significant joint destruction and debilitation.
Atopic dermatitis presents differently in infants compared to adults. Infants commonly get an eczematous rash that appears on the cheeks, outer surfaces of the arms and legs, and less commonly on the back, chest, and abdomen.11 In older children and adults, atopic dermatitis may develop on the inside of the elbows, backs of the knees and neck, as well as the palms of hands and soles of feet.11 Unlike in infants, atopic dermatitis in children and adults rarely affects the face.11 Of note, some people experience significant improvement in their atopic dermatitis when they reach adulthood.
What it Looks Like
The most common type of psoriasis is plaque psoriasis. As a result of rapid proliferation of keratinocytes, psoriasis patients classically develop well defined, red plaques with silvery scales.
The eczematous rash that characterizes atopic dermatitis is often preceded by an intense itch. It is often referred to “the itch that rashes.” The lesions are pink and classically appear “weepy” from ruptured blisters.11 Over time, the affected areas can become dry and cracked. Chronic lesions also develop a thickened, leathery appearance, termed lichenification.11
What Triggers it
Common psoriatic triggers include:5
- Stress: Increased stress can trigger the disease or exacerbate preexisting psoriasis5
- Injury to the skin: Psoriasis can appear in areas of skin injury or barrier disruption (i.e. trauma, surgery, tattooing, insect bites), known as the Koebner phenomenon12
- Medications: Lithium, antimalarials, imiquimod, beta blockers, interferons, bupropion, and nonsteroidal anti-inflammatory drugs can exacerbate psoriasis13,14
Infections: Various microorganisms that can trigger a psoriasis flare include, bacteria (streptococcus pyogenes, staphylococcus aureus), fungi (Malassezia, Candidida albicans), and viruses (papillomaviruses, retroviruses, endogenous retroviruses)14
Common atopic dermatitis triggers include:
- Dry skin: The skin of patients with atopic dermatitis is more dry at baseline. It is important for patients to routinely apply emollients to their skin to maintain skin barrier function, and a lapse in emollient application can trigger an atopic dermatitis flare.15
- Irritants: Substances that irritate the skin can exacerbate atopic dermatitis. Common culprits include hand soaps, laundry detergents, body wash, and surface cleaners with added fragrance or synthetic coloring. Other common irritants include, metals, cigarette smoke, wool, synthetic clothing, and antibacterial ointments.15
- Allergens: Allergens can exacerbate atopic dermatitis by both contact and inhalation. Common contact allergens include preservatives in medications, perfume-based products, latex, and metals.16 Examples of inhaled allergens include house dust mites (Dermatophagoides pteronyssinus and farinae), animal dander, tree and grass pollens, and molds.16
- Infection: Atopic dermatitis lesions can become easily infected, as the impaired skin barrier function allows for pathogens to more easily penetrate the epidermis. Common microorganisms that can provoke a flare include bacteria (staphylococcus aureus, and streptococcus species), viruses (molluscum, herpes simplex), and fungi (dermatophytes).16
Climate: Extreme temperatures can dehydrate the skin, leading to increased water loss which can cause an atopic dermatitis flare.
Which Medications Help
The mainstay of treatment for psoriasis and atopic dermatitis are topical corticosteroids. However, if the condition is severe, more potent medications may be warranted. It is important to be seen by a dermatology-trained professional for an accurate diagnosis and associated treatment plan.
- Mild disease or minimal body surface area: topical corticosteroids, calcipotriene (vitamin D derivative)
- More extensive body surface area involvement or if patient has a contraindication to other treatment methods: narrowband ultraviolet B (nbUVB)
- Moderate to severe disease with or without joint involvement: systemic agents such as apremilast, biologics (etanercept, adalimumab, ustekinumab, guselkumab, ixekizumab, etc.)
- Topical corticosteroids, topical calcineurin inhibitors are the mainstays of treatment
- Bleach baths or mupirocin applied intranasally for decolonization if patients frequently have bacterial infections
- For severe or refractory cases, dupilimab, a biologic medication, may be considered
- Diligent skin care with emollients and topical corticosteroids are essential for keeping atopic dermatitis under control