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tinea incognito

Tinea incognito

Tinea incognito also known as steroid-modified tinea or “tinea incognita”, is the name given to a fungal skin infection when the clinical appearance has been altered by inappropriate treatment, usually a topical steroid cream. The result is that the original infection slowly extends. Compared with untreated tinea corporis, tinea incognito usually displays a less raised margin, is less scaly, presents as more pustular, is more extensive and irritable and can thereby mimic other skin diseases (e.g. pemphigus foliaceus) 1. Often the patient and/or their doctor believe they have a dermatitis, hence the use of a topical steroid cream. The steroid cream dampens down inflammation so the condition feels less irritable. But when the cream is stopped for a few days the itch gets worse, so the steroid cream is promptly used again. The more steroid applied, the more extensive the fungal infection becomes and the less recognizable.

Figure 1. Tinea incognito

tinea incognito

Tinea incognito causes

Tinea incognito is due to dermatophyte fungal infection (tinea), most often when it affecting the trunk and/or limbs (tinea corporis). In a large retrospective study Romano et al. 2 analysed causative agents, clinical aspects, and sources of infection of 200 cases of tinea incognito. Tinea incognito was found to be due mainly to different Trichophyton and Microsporum species.

Anti-inflammatory creams that can induce tinea incognito include:

  • Topical steroids
  • Tacrolimus ointment
  • Pimecrolimus cream.

Tinea incognito can also be caused by systemic steroids.

Underlying diseases may predispose individuals to tinea infection, especially:

  • Immune suppressive drugs
  • Human immunodeficiency virus (HIV) infection
  • Diabetes mellitus.

Factors such as sweating, abrasion, and maceration also contribute to the development of tinea infection.

Tinea incognito differential diagnosis

Tinea incognito differential diagnosis includes lupus erythematosus, eczema, rosacea on the face, impetigo, purpura, seborrheic dermatitis, lichen planus, contact dermatitis, psoriasis and erythema migrans 2.

Tinea incognito prevention

Tinea incognito can be avoided if:

  • Patients do not use topical steroids to treat undiagnosed skin conditions
  • Medical practitioners consider the diagnosis of fungal skin infection in any scaly or pustular rash that has a prominent and irregular border, and is unilateral or asymmetrical in distribution
  • Mycology is performed when in doubt about the diagnosis of a scaly or pustular rash.

Tinea incognito symptoms

Compared with an untreated tinea corporis, tinea incognito:

  • Has a less raised margin,
  • Is less scaly,
  • More pustular,
  • More extensive,
  • And more irritable.

There may also be secondary changes caused by long term use of a topical steroid such as:

  • Atrophy (thin skin, stretch marks (striae) in the skin folds).
  • Purpura (bruising) and telangiectasia (broken blood vessels).

Tinea incognito diagnosis

The diagnosis of tinea is most easily made by taking skin scrapings for microscopy and culture a few days after stopping all creams. Adequate scrapings should be taken with the back of a scalpel blade from the advancing edge of the lesion. Adhesive tape (eg sellotape) stripping may be useful if scale is limited.

  • If there is little surface scale, the laboratory may report the specimen to be inadequate or negative.
  • After stopping a steroid cream, tinea incognito becomes very inflamed and more fungal elements may be seen on microscopy than usual.
  • The responsible organism generally grows promptly in culture.

If a skin biopsy is performed, the pathology of tinea incognito reveals the organisms.

Tinea incognito treatment

Any topical steroid or calcineurin inhibitor should be discontinued. Bland antipruritic lotions can be applied.

For milder cases treatment is normally with a topical antifungal agent such as terbinafine cream for one to two weeks or one of the imidazole creams for example, miconazole, ketoconazole, econazole for two to four weeks. Terbinafine is more expensive but slightly more effective.

But if the treatment is unsuccessful or the rash is very extensive or inflammatory (pustules present), oral antifungal medicines may be considered, including terbinafine and itraconazole.

References
  1. Tinea Incognito Hidden under Apparently Treatment-resistant Pemphigus Foliaceus. https://www.medicaljournals.se/acta/content/html/10.2340/00015555-0398
  2. Romano C, Maritati E, Gianni C. Tinea incognito in Italy: a 15-year survey. Mycoses 2006; 49: 383–387.
Health Jade Team

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