Sorting Out the Many Mimickers of Psoriasis


Of the many psoriasis mimicker clinicians are likely to encounter, atopic dermatitis is likely the most common one, especially the nummular eczema variant form.

“It has an earlier age of onset, usually in infancy, and can occur with the atopic triad that presents with asthma and seasonal allergies as well,” Israel David “Izzy” Andrews, MD, said at the virtual Pediatric Dermatology 2020: Best Practices and Innovations Conference. “There is typically a very strong family history, as this is an autosomal dominant condition, and it’s far more common than psoriasis. The annual incidence is estimated to be 10%-15% of pediatric patients. It has classic areas of involvement depending on the age of the patient, and lesions are intensely pruritic at all times. There is induration and crust, but it’s important to distinguish crust from scale. Whereas crust is dried exudate, and scale is usually secondary to a hyperproliferation of the skin. Initially, treatments (especially topical) are similar and may also delay the formalized diagnosis of either of the two.”

Another psoriasis mimicker, pityriasis rosea, is thought to be secondary to human herpesvirus 6 or 7 infection, said Dr. Andrews, of the department of dermatology at Phoenix Children’s Hospital. It typically appears in the teens and tweens and usually presents as a large herald patch or plaque on the trunk. As the herald patch resolves, smaller lesions will develop on the trunk following skin folds. “It’s rarely symptomatic and it’s very short-lived, and clears within 6-12 weeks,” Dr. Andrews noted. “It can present with an inverse pattern involving the face, neck, and groin, but sparing the trunk. This variant, termed inverse pityriasis rosea, can be confused with inverse psoriasis, which has a similar distribution. However, the inverse pattern of pityriasis rosea will still resolve in a similar time frame to its more classic variant.”

Pityriasis lichenoides can also be mistaken for psoriasis. The acute form can present with erythematous, scaly papules and plaques, but lesions are often found in different phases of resolution or healing. “This benign lymphoproliferative skin disorder can be very difficult to distinguish from psoriasis and may require a biopsy to rule in or out,” Dr. Andrews said. “It can last months to years and there are few treatments that are effective. It is typically nonresponsive to topical steroids and other treatments that would be more effective for psoriasis, helping to distinguish the two. It is thought to exist in the spectrum with other lymphoproliferative diseases including cutaneous T-cell lymphoma [CTCL]. However, there are only a few cases in the literature that support a transformation from pityriasis lichenoides to CTCL.”

Seborrheic dermatitis is more common than atopic dermatitis and psoriasis, but it can be mistaken for psoriasis. It is caused by an inflammatory response secondary to overgrowth of Malassezia yeast and has a bimodal age distribution. “Seborrheic dermatitis affects babies, teens, and tweens, and can persist into adulthood,” he said. “Infants with cradle cap usually resolve with moisturization, gentle brushing, and occasional antifungal shampoos.” Petaloid seborrheic dermatitis can predominately involve the face with psoriatic-appearing induration, plaques, and varying degrees of scales. “In skin of color, this can be confused with discoid lupus, sarcoidosis, and psoriasis, occasionally requiring a biopsy to distinguish,” said Dr. Andrews, who is also an assistant professor of pediatrics at the Mayo Clinic College of Medicine and Science in Scottsdale, Ariz.

Another psoriasis mimicker, pityriasis amiantacea, is thought to be a more severe form of seborrheic dermatitis. It presents with concretions of scale around hair follicles that are highly adherent and are sometimes called sebopsoriasis. “It may be associated with cutaneous findings of psoriasis elsewhere, but may also be found with secondarily infected atopic dermatitis and tinea capitis; however, in my clinical experience, it is most often found in isolation,” he said. “There may be a seasonal association with exacerbation in warm temperatures, and treatment often consists of humectants like salicylic acid for loosening scale, topical steroids for inflammation, and gentle combing out of scale.”

Infections can also mimic psoriasis. For example, tinea infections are often misdiagnosed as eczema or psoriasis and treated with topical steroids. “This can lead to tinea incognito, making it harder to diagnose either condition without attention to detail,” Dr. Andrews said. “On the body, look for expanding lesions with more raised peripheral edges, and central flattening, giving a classic annular appearance. It’s also important to inquire about family history and contacts including pets, contact sports/mat sports (think yoga, gymnastics, martial arts), or other contacts with similar rashes.” Work-up typically includes a fungal culture and starting empiric oral antifungal medications. “It is important to be able to distinguish scalp psoriasis from tinea capitis to prevent the more inflammatory form of tinea capitis, kerion (a deeper more symptomatic, painful and purulent dermatitis), which can lead to permanent scarring alopecia,” he said.

Bacterial infections can also mimic psoriasis, specifically nonbullous impetigo and ecthyma, the more ulcerative form of impetigo. The most frequent associations are group A Streptococcus, methicillin-susceptible Staphylococcus aureus and methicillin-resistant S. aureus.

Dr. Andrews closed his presentation by noting that tumor necrosis factor–alpha inhibitor–induced psoriasiform drug eruptions can occur in psoriasis-naive patients or unmask a predilection for psoriasis in patients with Crohn’s disease, juvenile idiopathic arthritis, or other autoinflammatory or autoimmune conditions. “They may improve with continued treatment and resolve with switching treatments,” he said. “Early biopsy in psoriasiform drug eruptions can appear like atopic dermatitis on pathology. When suspecting psoriasis in a pediatric patient, it is important to consider the history and physical exam as well as family history and associated comorbidities. While a biopsy may aide in the work-up, diagnosis can be made clinically.”

Dr. Andrews reported having no financial disclosures.

This article originally appeared on MDedge.com.





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