Identifying tinea incognito

A skin condition that is not what it often seems to be.

CASE HISTORY
A 76-year-old farmer presented to his GP with a two-year history of an itchy, red rash that began in his groin and subsequently spread to his inner thighs and upper extremities.

Figure 1: tinea incognito on the inner surface
of the thigh.

Figure 2: dorsal surface of the hand in the
same patient. Note the absence of scale
typical for most tinea corporis infections.

There was no background history of childhood eczema or asthma. He had been treated unsuccessfully in the past with a variety of topical steroid creams for what was initially thought to be eczema due to the chronicity of the rash and clinical presentation.

Physical exam revealed pink, hyperpigmented patches with minimal scale and areas of slight atrophy along the groin, inner thighs, forearms and dorsum of hands bilaterally.

Based on the long history of an itchy rash, unresponsive to steroids, the GP decided to obtain a skin scraping and hair pluckings for microscopic evaluation, as well as two punch biopsies for histopath­o­logy and fungal culture.

Microscopy revealed translucent, branching hyphae, and tinea incognito was diagnosed. Treatment with oral griseofulvin 500 mg/day was initiated, and the patient was instructed to discontinue all topical steroids. 

 
BACKGROUND
The term tinea incognito (literally tinea ‘in disguise’) is used to describe a dermatophyte infection of the skin in which the clinical presentation has been altered, typically by the application of topical steroids.^1,2,5,6,9

This dermatological entity differs from other fungal infections such as tinea corporis in that tinea incognito often lacks the characteristic ‘ringworm’ features.¹ Tinea incognito tends to have more extensive skin involvement, pustules, worse pruritus and less scaling than other types of tinea infections.^1,2

This can often lead to a delay in diagnosis or misdiagnosis. Patients may suffer for months to years with an undiagnosed dermatophyte infection that can cause significant morbidity, including anxiety, distress, discomfort and pain. Therefore, it is important for clinicians to be familiar with this masked dermatophyte infection.

An accurate diagnosis is essential, as patients with tinea incognito are often inappropriately treated with topical steroids, which not only allow the fungal infection to flourish, but can lead to changes in the skin such as atrophy, striae and telangiectasias.⁵

Clinicians should also be aware that it is not unusual for patients to report an initial improvement in their rash due to the anti-inflammatory properties of the steroids; however, this improvement is short-lived as the symptoms return with a vengeance when the topical steroids are discontinued.⁵

 
AETIOLOGY
Ringworm infections are very common dermatoses seen in all ages throughout the world.^3,9

Dermatophytes are most commonly acquired via human-to-human contact; however, contact with domesticated animals, livestock and fomites may also spread the infection.²

Dermatophytes prefer the moist, warm environment of dead, keratotic skin and rarely invade deeper than the epidermis.² As with tinea corporis, the most common mycotic organisms responsible for tinea incognito are Trichophyton rubrum, Microsporum canis and T. mentagrophytes, with T. rubrum being the most common worldwide.^4,6,7

 
DIFFERENTIAL DIAGNOSIS

• Eczema
• Contact dermatitis
• Candidiasis
• Rosacea
• Seborrhoeic dermatitis
• Subacute cutaneous lupus erythematosus
• Psoriasis
• Syphilis.

 
DIAGNOSIS
When a mycotic skin infection is suspected, skin scrapings are indicated. The presence of branching hyphae upon microscopic evaluation with 10% potassium hydroxide (KOH) is indicative of a dermatophyte infection.^1,5,7

Recent use of steroids may make obtaining scale difficult. In this case, it is best for the steroid to be discontinued for two to three days before attempting to gather skin scrapings.⁷

Skin samples may also be sent for fungal culture to aid in diagnosis, particularly if the clinical picture suggests tinea, yet the microscopic exam with KOH is non-confirmatory.

Skin biopsies are not necessary for the diagnosis of tinea incognito, but may reveal a non-specific, spongiotic, cellular inflammatory infiltrate along the superficial dermis and epidermis.⁹

Staining with periodic acid-Schiff (PAS) is more useful in that it may reveal positively staining fungal hyphae within the stratum corneum.⁹

 
TREATMENT
While topical fungistatic agents such as econazole and ketoconazole are sufficient to treat most forms of localised tinea corporis, tinea incognito requires systemic treatment with an oral antifungal such as itraconazole or fluconazole.²

Clinicians should be mindful of potential drug interactions, as azoles can lead to cytochrome p450 enzyme inhibition. Oral griseofulvin or terbinafine is also useful in the treatment of tinea incognito, and while no single antifungal agent has been shown to be superior in efficacy, griseofulvin is much cheaper.

Males need to be advised not to get their partner pregnant while taking griseofulvin, as it can affect sperm. Steroids have no role in the treatment of tinea infections and should be discontinued once the diagnosis has been made.

Not infrequently patients may report an initial flare-up of their skin when discontinuing topical steroids and beginning antifungal therapy.⁵

Often this is short-lived and well tolerated, but it may be helpful for the clinician to discuss this in advance so patients are not alarmed and do not re-start topical steroids.

The duration of antifungal treatment is variable and may range from one month to three months for more recalcitrant infections.²

Clinicians should always consider tinea incognito in a patient with an itchy rash that does not resolve with steroid use.

Mary Alice Nading, medical student, Vanderbilt University School of Medicine, Nashville, TN, USA; and Associate Professor Dedee F. Murrell, MA(Cambridge), BMBCh(Oxford), FAAD(USA), MD(UNSW), Head, Department of Dermatology, St George Hospital, UNSW, Sydney, NSW.

 
REFERENCES

1. Ive FA, Marks R. Tinea Incognito. Br Med J 1968;3:149-52.
2. Jacobs JA, Kolbach DN, Vermeulen AHM, Smeets MHMG, Neuman HA. Tinea incognito due to Trichophyton rubrum after local steroid therapy. Clin Infect Dis 2001;33:e142-e144.
3. Sanchez-Castellanos ME, Mayorga-Rodriguez JA, Sandoval-Tress C, Hernandez-Torres M. Tinea incognito due to Trichophyton mentagrophytes. Mycoses 2007;50:85-87.
4. Romano C, Maritati E, Gianni C. Tinea incognito in Italy: a 15-year survey. Mycoses 2006;49:383-87.
5. Oklota CA, Brodell RT. Uncovering tinea incognito. Postgraduate Medicine 2004;116:65-66.
6. Gorani A, Schiera A, Oriani A. Case Report. Rosacea-like Tinea incognito. Mycoses 2002;45:135-37.
7. Elgart ML. Tinea Incognito: an update on Majocchi granuloma. Dermatol Clin 1996;14:51-55.
8. Solomon BA, Glass AT, Rabbin PE. Tinea incognito and “over-the-counter” potent topical steroids. Cutis 1996;58:295-96.
9. Lin RL, Szepietowski JC, Schwartz RA. Tinea faciei, an often deceptive facial eruption. Int J Dermatol 2004;43:437-40.