I recently received an email from a new patient seeking help for extremely painful blistering to one foot. As the patient worked in a hot environment wearing safety footwear for long shifts this condition was seriously affecting the patient’s mobility and ability to perform at work.
Suspecting a simple case of blistering due to hyperhidrosis and footwear, imagine my surprise when faced with an inflamed, intensely itchy, blistered foot. This 30-year-old female patient had a short history of blistering to the arch of the right foot. On examination she also had peeling of the skin, vesicles and erythema up to Wallace’s line of both feet (figure 1). The diagnosis was common, but the presentation unusual – bullous tinea pedis (BTP).
Rapid blistering on the feet
The patient was in good health and on no regular medication with no family history of any skin conditions. When a patient presents with blisters on the foot, a history and examination would be essential to establish a diagnosis. The list of differential diagnosis would look like this:
Friction Blisters: A common cause of unliteral and bilateral blistering, typically on a pressure bearing areas related to rubbing of footwear or hosiery. The history usually holds the key, with a recollection of increasing pain during prolonged activity in specific footwear.
Dyshidrosis/pompholyx: Characterized by small, deep-seated intensely itchy vesicles on the palms, soles, and sides of the fingers and toes. It would be important to examine the toes and hands for signs of tiny blisters as a clue to the diagnosis. There is a normally a background of hyperhidrosis, atopy or nickel allergy.
Contact dermatitis: Vesicular eruptions may occur in response to irritants or allergens in the skin. On the sole of the foot, contact dermatitis is unusual and requires prolonged damp conditions and a re-exposure to an allergen such as a topical product, shoe dye or glue typically. The area affected would be well demarcated to the point of contact, typically bilateral with a background of erythema and profound skin shedding.
Herpes simplex virus infection: This is very unusual on the foot. Tiny, white, vesicles are typically grouped or clustered and often accompanied by systemic symptoms.
Bullous pemphigoid: Characterized by rapidly forming tense bullae on the skin and mucous membranes. The condition is almost exclusive to patients over 70 and begins with itching before any blisters appear. They rapidly form as tense bullae and break easily leaving sore erosions. They typically occur anywhere below the umbilicus and are bilateral and can be widespread.
Dermatitis herpetiformis: Associated with coeliac disease and presents with small, clustered intensely pruritic, papules and vesicles. Lesions tend to be only a few millimetres in diameter. They are a cutaneous manifestation of coeliac disease most commonly arising in the 15-50 age group. Typically, these would be on the scalp, shoulders, buttocks, elbows and knees. However, they are rarely observed on the foot.
Bullous Impetigo: Pus filled blisters due to Staph. aureus infection which tend to spontaneously rupture leaving a scaly rim or honey coloured crust. The condition is highly contagious featuring most frequently in younger children on the face. In adults, a bullous presentation on the legs is more common.
Tinea Pedis
Fungal foot infection, both of the skin and nail, is a very common problem, affecting around one third of adults in the UK and Europe [1]. As we age, fungal infection becomes more prevalent, with an estimated 50% of those in their 6th decade affected. The vast majority of fungal foot infection is caused by dermatophyte fungi [2, 3]. In its most subtle form, it is often missed or misdiagnosed [4, 5] and can spread to other areas of the body including the nails, hands and groin if left untreated. Its detrimental effects on skin integrity can lead to secondary bacterial infection. Tinea pedis is a recognised risk factor for cellulitis [6], particularly in those with diabetes [7].
Bullous Tinea Pedis
As podiatrists, we frequently see the various presentations of fungal infections of the skin – moccasin, vesicular and interdigital presentations. In the nails – superficial white, distal-lateral subungual, proximal subungual, total dystrophic and endonyx mycosis. The bullous variety is the least common skin presentation, which is rarely discussed but manifests as a florid form of tinea pedis.
Its rarity can present a diagnostic challenge to differentiate it from other blistering conditions (as discussed above).
BTP most often affects the feet [8] and was first described in 1922 by Alexander [9], although it was not until 1952 that Costello [10] describe a case of bullous tinea which tested positive for culture of T. rubrum and proved its causation.
How does Bullous Tinea Pedis present?
It typically presents unilaterally [8] with large, serous fluid-filled blisters on the plantar and lateral surfaces of the feet. These blisters can be solitary or multiple, and are often accompanied by erythema, scaling, and maceration as seen in other presentations of tinea pedis.
Pruritus and burning may be present. Unlike other vesicular dermatoses, the blisters in bullous tinea pedis tend to be tense and superficial containing a clear fluid [11]. Most tinea pedis occurs in adults although previous research found in a cohort of 80 schoolchildren with confirmed tinea pedis, reported around 10% had the bullous form of the disease [12].
Bullous TP, unlike the more common moccasin and interdigital forms, can be itchy but also painful affecting a patient’s mobility and quality of life as observed in this patient, driving them to seek treatment.
According to surveys, T. rubrum is the causative organism for the majority of tinea pedis infections, and approximately 76% of all dermatophyte infections (7). In contrast, bullous tinea is most often caused by the dermatophyte Trichophyton mentagrophytes var. interdigitale in adults, and although less common, T rubrum has been isolated from blisters in adults [13] and childhood cases of BTP [14].
Potential Complications.
While bullous tinea pedis is generally easily treated with topical antifungals, complications can arise if treatment is delayed. Secondary bacterial infection can occur. Pus filled vesicles are an early indicator of secondary bacterial infection [11].
It is important to remember the signs and symptoms of this presentation, as there is a risk of cellulitis from secondary bacterial infection should the blisters burst or deroof which is likely, particularly if the patient breaks the skin due to the intense itch that often accompanies it. Broken vesicles can lead to the development of a rare form of the disease – ulcerative tinea pedis [15], which is particularly invoked when secondary bacterial infection arises locally leading to widespread plantar skin breakdown.
Patients are likely to have already tried other treatments, such as topical steroids, due to it being mistaken for an inflammatory dermatosis. Remember, when presented with blistering, to look for other signs of tinea – scale, vesicles, interdigital maceration, for clues to the diagnosis.
Bullous tinea can also be associated with the dermatophytid or ID reaction [16]. This is where a corresponding vesicular eruption may arise remotely on the palms (from which no fungal infection can be isolated) so be sure to check if the patient has symptoms other than on the feet!
Bullous tinea will generally response to the usual topical antifungals, along with other hygiene measures to prevent reinfection and improve skin integrity. The patient may need reassurance that there is not a more serious underlying cause for this distressing presentation. In this case rapid improvement was seen in terms of both symptoms and presentation within 2 weeks use of 1% topical terbinafine cream.
Authors note: Full consent from the patient was given for this case to be published.
References
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