Skin rashes can be tricky even for seasoned clinicians. Among the most confounding cases in dermatology are tinea infections that mimic psoriasis. Tinea, a superficial fungal infection, can present with red, scaly plaques just like psoriasis, often leading to misdiagnosis and incorrect treatment. When mistaken for psoriasis, tinea may be treated with topical steroids, which can worsen the infection and lead to atypical presentations like tinea incognito. Recognizing the subtle differences is critical for dermatologists, general practitioners, and even patients navigating persistent or confusing skin conditions.
What is Tinea?
Tinea, also known as dermatophytosis, is a fungal infection of the skin caused by dermatophytes such as Trichophyton, Microsporum, and Epidermophyton species. Depending on the area affected, it has different names:
- Tinea corporis – body
- Tinea cruris – groin
- Tinea capitis – scalp
- Tinea pedis – feet
- Tinea faciei – face
Tinea usually appears as annular, scaly patches with central clearing and a raised, active border. However, this textbook presentation isn’t always present, especially if topical corticosteroids have been applied, masking classic features.
Psoriasis and Its Look-Alikes
Psoriasis is a chronic autoimmune skin disorder marked by sharply demarcated, red plaques with silvery scales, commonly appearing on the elbows, knees, scalp, and lower back. It is non-infectious and typically symmetrical. However, early tinea infections can sometimes closely resemble plaque psoriasis, especially when:
- The scaling is prominent
- The lesion margins are not clearly raised
- The central clearing is not well-defined
- The infection involves atypical areas, like the scalp or intertriginous zones
This mimicry is especially problematic when the patient receives topical corticosteroids, leading to partial suppression of inflammation and altered presentation, a condition called tinea incognito (Kumar & Bishnoi, 2021).
Tinea Incognito: A Fungal Disguise
When a tinea infection is incorrectly treated as psoriasis, the use of topical steroids may reduce redness and inflammation temporarily. However, this suppresses immune response, allowing the fungus to spread unchecked. The resulting tinea incognito presents with:
- Less defined borders
- Increased itch
- More widespread involvement
- Atypical appearance lacking the usual annular pattern
This condition can mimic seborrheic dermatitis, eczema, or psoriasis, creating significant diagnostic confusion (Verma & Madhu, 2017).
Key Differences Between Tinea and Psoriasis
| Feature | Tinea | Psoriasis |
|---|---|---|
| Cause | Fungal infection | Autoimmune disorder |
| Borders | Raised, active, well-defined | Well-demarcated but not raised |
| Central Clearing | Often present | Absent |
| Scaling | Peripheral | Diffuse over lesion |
| Itch | Prominent | Variable |
| Distribution | Asymmetric, random | Often symmetric and predictable |
| Response to Steroids | Worsens | Improves temporarily |
In ambiguous cases, a potassium hydroxide (KOH) preparation, fungal culture, or skin biopsy may be necessary to confirm the diagnosis.
The Risk of Misdiagnosis
Misidentifying tinea as psoriasis or eczema can lead to inappropriate treatment with:
- Topical steroids: worsening fungal infection
- Immunosuppressive agents: increasing systemic spread
- Delay in antifungal therapy: prolonging discomfort and transmission risk
A study from India, where dermatophytosis is highly prevalent, revealed that over 30% of tinea cases were initially misdiagnosed due to atypical presentation or steroid use (Lacarrubba et al., 2015).
Treatment and Management
Once diagnosed accurately, tinea can be effectively treated with:
- Topical antifungals: clotrimazole, terbinafine, ketoconazole for mild cases
- Oral antifungals: terbinafine or itraconazole for widespread or resistant infections
- Discontinuation of steroids: to prevent immunosuppression and recurrence
Patients should also be educated on hygiene practices, laundering clothes and linens, avoiding shared personal items, and keeping skin dry to prevent reinfection.
When to Suspect Tinea in Psoriasis-Like Lesions
- The rash worsens with steroid creams
- New lesions appear after partial improvement
- There is intense itching
- There is a family or community history of tinea
- There is unilateral or asymmetric distribution
When in doubt, dermatologic testing such as KOH mount, fungal culture, or dermoscopy can help confirm the diagnosis.
Tinea infections that mimic psoriasis are a diagnostic pitfall that can lead to inappropriate treatments and prolonged suffering. Recognizing atypical presentations, especially tinea incognito, is essential for effective management. Clinicians must maintain a high index of suspicion when faced with steroid-resistant or asymmetric rashes, and patients should be informed about the risks of self-treatment. A fungal infection posing as an autoimmune disease reminds us that not all that scales is psoriasis.
References
- Kumar, N., & Bishnoi, A. (2021). Tinea incognito: The hidden dermatophytosis. Indian Dermatology Online Journal, 12(1), 4–10. https://doi.org/10.4103/idoj.IDOJ_180_20
- Verma, S., & Madhu, R. (2017). The great imitator: Tinea incognito masquerading as other dermatoses. Journal of Clinical and Diagnostic Research, 11(4), WD01–WD02. https://doi.org/10.7860/JCDR/2017/24861.9642
- Lacarrubba, F., Verzì, A. E., Micali, G. (2015). Tinea incognito: A great imitator. Clinical, Cosmetic and Investigational Dermatology, 8, 455–459. https://doi.org/10.2147/CCID.S84758
- Ameen, M. (2010). Epidemiology of superficial fungal infections. Clinical Dermatology, 28(2), 197–201. https://doi.org/10.1016/j.clindermatol.2009.12.005
- Bolognia, J. L., Schaffer, J. V., & Cerroni, L. (2018). Dermatology (4th ed.). Elsevier.
