In previous articles I have mentioned how common fungal foot infections are, with Trichophyton rubrum being the “master” of subtlety. As a result, many fungal foot infections go untreated and unnoticed by the patient and podiatrist alike. Clinical symptoms with T rubrum is often subdued owing to it anthrophillic preference (adaptation to live successfully on human epidermis). The soles of the feet may exhibit just slight dryness with a white, dusty or chalky appearance in the creases. There may even be minor nail changes evidence on close examination. This low visibility (or some would say invisibility) is a well-known fact in dermatology.
Tinea ascending the leg in a patient using topical steroids. Note the fungal "fringe".
For some patients with tinea, they may be misdiagnosed or not diagnosed at all. Consequently, whether prescribed or self-purchased incorrectly, they may apply a topical corticosteroid. As we are aware topical corticosteroids are drugs well known for there immune-suppressive capabilities. Consequently, a cream applied to a rash that is tinea in nature will suppress the normal immune response in the skin and give the fungal infection a free reign to spread further. Not only that, but the clinical appearance will change becoming less like normal tinea - scale with a potential red edge (on non-glaborous skin) and more like dermatitis/eczema potentially becoming a less vivid colour, or exhibiting a variable range of symptoms including erythema, pustulation, pruritus and extension to sites not typical for fungal infection.
The clinical effect the steroid had on the tinea infection was termed “tinea incognito” by Ive & Marks in 1968 (1). The fourteen cases they reviewed included one patient who had applied a potent steroid to her feet under occlusion (something which should generally be avoided without medical direction). This had caused the rash to spread above the ankles. However, upon cessation of the steroids and administration of griseofulvin and application of Whitfield’s ointment (remember this was 1968) it resolved, unremarkably.
As a podiatrist I remember seeing a lady who had been applying steroid cream (she had been keeping from a previous skin problem) to some scale on her foot. As she described it, “the rash just went wild” and spread up her leg. By the time of her appointment it was half way up the shin! A quick switch to clotrimazole had the rash under control in less than week. So, when it comes to assessment, one of the key questions to ask is what previous treatments has the patient tried or applied? This can be vital information.
Since the term “tinea incognito” was adopted in 1968 there have been some questions raised about the definition and terminology. Firstly, Verma has pointed out incorrect nomenclature. The Latin noun “Tinea” is feminine gender and therefore the adjective “incognito” that follows it should also be feminine gender, i.e., “incognita” (2). He goes on to make the point that since its discovery, all dermatologists should be aware of the clinical condition so how can it remain “incognito”? A good point made.
Going back to my opening paragraph, the idea that tinea does so often present subtly, and not necessarily due to steroid either, is that not suitable to be awarded the term incognito? Sharing my view are Atzori and colleagues. In a paper published in 2012 (3), they identified 154 cases in their locality where tinea infections had presented and been missed. They suggested around 2.5% of all tinea infections may escape diagnosis on first assessment with additional cases failing laboratory testing further reducing the clinicians suspicion for the condition. Consequently, they conclude that an atypical appearance of tinea is not just a steroid phenomenon but high variability in presentation arises due to several factors including fungal virulence, host factors and environment. Consequently, they suggest the term “tinea atypia” as a more suitable clinical term.
As a podiatrist, I think the message is very clear. Tinea pedis is the most common of all tinea infections observed on the body and a very common condition on the foot. Therefore, with any patient presenting with foot skin problem, the clinician should have the diagnosis in the forefront of their mind and take steps to rule this in or out. “Common things occur commonly” as I was once told – a simple, almost idiotic statement which strangely holds some truth.
References
1. Ive FA, Marks R. Tinea Incognito. Br Med J. 1968;3(5611):149-52.
2. Verma S. A closer look at the term tinea incognito; A factual as well as grammatical inaccuracy. Indian J Dermatol. 2017;62(2):219-20.
3. Atzori L, Pau M, Aste N, Aste N. Dermatophyte infections mimicking other skin diseases: a 154-person case survey of tinea atypica in the district of Cagliari (Italy). Int J Dermatol. 2012;51(4):410-5.