Psoriasis and eczema (atopic dermatitis) are two prevalent chronic inflammatory skin conditions. While often viewed as separate diseases, a person can experience both simultaneously, though this dual diagnosis is relatively uncommon. This overlap presents a unique diagnostic and therapeutic challenge for dermatologists, requiring an integrated approach that targets shared inflammatory mechanisms.
Defining Eczema and Psoriasis
Eczema is an inflammatory skin condition characterized by intense itching and a compromised skin barrier function. It is primarily driven by a Type 2 helper T-cell (Th2) immune response, involving cytokines like Interleukin-4 (IL-4) and Interleukin-13 (IL-13). Lesions often appear as red patches with ill-defined borders, typically located in skin folds, such as the inside of the elbows and behind the knees. The intense itching is a hallmark symptom.
Psoriasis is an immune-mediated disease driven mainly by a Th1 and Th17 immune response. This T-cell activation triggers the accelerated growth of skin cells, leading to a rapid buildup. The resulting lesions are thick, raised plaques with sharply defined borders, often covered in silvery-white scales. These plaques most commonly occur on extensor surfaces, including the outside of the elbows and knees, the scalp, and the lower back.
The Reality of Coexistence
A simultaneous diagnosis of eczema and psoriasis is recognized in clinical practice, sometimes called Eczema-Psoriasis Overlap Syndrome. This coexistence is possible because both conditions share an underlying foundation of immune system dysregulation and chronic inflammation.
In patients with the overlap syndrome, inflammation markers associated with both diseases are often elevated. Studies show that Interleukin-17 (IL-17), a cytokine central to psoriasis, is significantly higher in patients with both conditions than in those with only one. The reported prevalence varies widely, ranging from under one percent to over 16 percent in some studies, likely due to a lack of standardized diagnostic criteria. The presentation can manifest as a true overlap with distinct lesions, or as one condition transforming into the other, sometimes triggered by certain treatments.
Clinical Differentiation and Diagnosis
Distinguishing between the two conditions requires careful clinical assessment. Observation focuses on lesion characteristics, such as ill-defined eczematous plaques versus well-demarcated silvery psoriatic scales. The location of the rash is also a significant clue, noting the classic flexural involvement of eczema versus the extensor surface involvement of psoriasis.
When the clinical picture remains ambiguous, a skin biopsy for histopathology is often necessary for confirmation. Psoriasis typically shows psoriasiform hyperplasia and collections of neutrophils, while eczema is characterized by spongiosis (fluid accumulation between skin cells). In a true overlap case, the biopsy may reveal features of both pathologies, such as psoriasiform hyperplasia coexisting with mild spongiosis. Analysis of specific molecular markers, such as IL-36 and beta-defensin 2, can further help identify an underlying psoriasis-like Th17 phenotype in ambiguous cases.
Integrated Management Approaches
Managing patients with both conditions requires an integrated approach, as treatments for one disease may aggravate the other. Topical therapies, including corticosteroids and calcineurin inhibitors, remain the first line of defense, but require careful monitoring. Aggressive psoriasis treatments, such as those targeting the IL-17 pathway, can sometimes induce an eczematous reaction known as paradoxical eczema.
Systemic treatments target inflammatory pathways common to both diseases. Janus Kinase (JAK) inhibitors are options because they broadly inhibit the Th1 and Th2 immune pathways involved in both conditions. Biologic agents targeting Interleukin-23 (IL-23) are also preferred for overlap cases, as they are less likely to induce atopic-like eczema. Furthermore, lifestyle management is important, encompassing consistent gentle skincare, meticulous moisturization, and avoiding known environmental triggers.