Clinical REVIEW Fungal foot infection: the hidden enemy? When discussing tissue viability in the lower limb, much attention is focused on the role of bacterial infection. However, fungal skin infection is a more frequent and more recurrent pathogen which often goes undetected by the practitioner and patient alike. Potentially, untreated fungal foot infection can facilitate secondary problems such as superficial bacterial infections, or, more seriously, lower limb cellulitis. Often simple measures can prevent fungal foot infection and therefore reduce the possibility of complications. This article will review the presentation of tinea pedis and onychomycosis, their effects and management. Ivan Bristow, Manfred Mak Under occlusive and humid conditions increased risk of acquiring the infection. KEY WORDS the fungal hyphae then develop and Patients with diabetes show an increased invade the deeper stratum corneum. susceptibility (Yosipovitch et al, 1998). Fungal Nutrition is afforded by the extra-cellular Boyko et al (2006) have identified the Tinea pedis secretion of proteolytic and keratolytic presence of tinea to be a predictor of Onchomycosis enzymes breaking down the complex foot ulceration in a diabetic population. Cellulitis keratin into simple molecules which can The reason for an increased prevalence be absorbed by the organism (Kaufman in patients with diabetes remains under- et al, 2007). researched. It has been proposed that peripheral neuropathy renders the foot Epidemiology of fungal foot infection insensate reducing individual awareness inea pedis (athlete’s foot) is an Fungal foot infection (FFI) is the most to the presence of infection. Eckhard et inflammatory condition and common infection found on the foot. al (2007) discovered a high prevalence Trepresents the most common of Seldom seen before puberty, the in patients with type 2 diabetes who all the superficial fungal skin infections prevalence rises with age, peaking in the exhibited a lack of sweating when tested (Hay, 1993). Predominantly, it is 60-year plus age group with around 50% with the Neuropad® (Ark Therapeutics), caused by a group of fungi specifically showing evidence of FFI (Pierard, 2001). which indicates sudomotor activity. They adapted to living on the skin known as The disease affects males three times postulated that the absence of sweat dermatophytes. Although there are a more frequently than females (Gupta et production altered skin barrier function. In few other causative species (Table 1), al, 1998). The Achilles project (Roseeuw, vitro, it has been demonstrated that sweat by far the most common isolate from 1999) reviewed over 96,000 patients secretions contain acidified nitrite which the foot is Trichophyton rubrum, a highly for the presence of foot disease across has fungicidal activities (Weller et al, 2001). specialised dermatophyte which has 20 European countries and found 35% adapted to residing within the human of subjects to have fungal foot infection Therefore, it could be suggested that epidermis (Weitzman and Summerbell, (tinea pedis, onychomycosis or both). In a lack of production may render the 1995). The infection is propagated addition it has been shown that countries individual more susceptible to invasion. from person to person when fungal with longer winters demonstrated higher The interaction between dermatophytes arthroconidia on shed skin squames infection rates, presumably because of the and the immune system has been studied adhere to the soles of others by way of longer time more occlusive footwear was and it has been demonstrated that T adherent fibrils (Kaufman et al, 2007). being worn (Djeridane et al, 2006). rubrum has the ability to inhibit the normal phagocytic process (Campos et al, 2006). Studies focusing on cancer patients, Moreover, in patients with diabetes, smokers and those with peripheral hyperglycaemia itself has been shown to Ivan Bristow is Lecturer, School of Health Sciences, vascular disease (PVD) (Virgili et al, 1999; decrease phagocytic activity further, thus University of Southampton; Manfred Mak is Podiatrist, Gupta et al, 2000; Sigurgeirsson and compounding the problem (Weekers et Singapore General Hospital, Singapore Steingrimsson, 2004) have all reported an al, 2003). 72 Wounds UK, 2009, Vol 5, No 4 Bristow final CS4.indd 2 28/10/2009 16:50 Clinical REVIEW Recognition and diagnosis For most patients, fungal skin infection Classically, tinea pedis is reported as an can be diagnosed on clinical grounds acute, itchy infection accompanied by alone. However, if systemic antifungal vesiculation and erythema or as inter- therapy is being considered, to minimise digital fissuring and maceration. In practice, the risks of potential, although rare, side- clinical recognition of the disease can be effects, microbiological confirmation is more difficult due to its subtle appearance. advised (Bell-Syer et al, 2002). Diagnosis In particular, T rubrum, the most common can be confirmed by way of a nail cause of foot infection, may produce few clipping or skin scraping from the affected Figure 1. Tinea pedis — as a subtle plantar symptoms other than dry plantar skin from foot. Disappointing laboratory results infection recognised as the dry, dusty appearance. which itching is frequently absent (Bristow, often come back as negative despite 2004; Mayser et al, 2004). Clinically, the overwhelming clinical evidence of infection may resemble dry skin, the infection. A successful sample requires the only clue being a dry, chalky appearance practitioner to collect viable fungus within exaggerated in the skin creases on the the skin/nail sample. Strategies which may sole of the foot (Figure 1); a place typically help to do this are listed below: overlooked when seeking an infection. As 8 When taking a nail clipping, if available there are frequently no symptoms, patients include skin scrapings from the affected and practitioners alike are unaware of the foot as well Figure 2a. Distal sub-ungual onychomycosis 8 presence of the infection (Maruyama et al, Include sufficient material for the secondary to tinea pedis. Note the signs of skin 2003). The plantar surface is a frequently laboratory to work with infection surrounding the nail. overlooked area and it has been suggested 8 When taking a nail clipping, try and that this part of the foot, in particular, obtain material from the proximal acts as a fungal reservoir from which the edge of the infected nail as this is infection can spread (Szepietowski et where most of the viable fungus is al, 2006). Consequently, it is important likely to be. Evidence from a study of to assess other areas of skin for a co- 194 patients demonstrated that the existing fungal infection. Concomitant more proximal the sample collection, dermatophyte infections are particularly the greater the chances of acquiring a common on the hands (tinea mannum), positive culture (Shemer et al, 2007). Figure 2b: White superficial onychomycosis. groin (tinea cruris) and fingernails Inclusion of sub-ungual nail debris from (Szepietowski et al, 2006). this area can also be helpful 8 Vertically drilling a hole in the nail and When the disease is established on collecting sub-ungual material from the foot, the infection may also spread the proximal infected edge has been to the toenails causing onychomycosis. shown to be particularly effective at Typically, dermatophytes spread under yielding more viable fungi for culture the nail free edge (or hyponychium) testing (Shemer et al, 2009) onto the nail bed — this is termed ‘distal 8 As an adjunct or alternative, skin sub-ungual invasion’ (Figure 2a) and may and nail samples may be tested for Figure 2c: Total nail dystrophy. gradually spread proximally towards the the presence of dermatophytes nail producing cells, the nail matrix. Other using the periodic acid schiff (PAS) given negative results but clinical common variants are white superficial stain. A number of studies have suspicion of fungal infection is still onychomycosis (Figure 2b), typically caused confirmed the high sensitivity of this high (Weinberg et al, 2005). by T interdigitale, and total nail dystrophy test over more traditional methods (Figure 2c), which occurs when the such as potassium hydroxide (KOH) Complications of the untreated disease infection advances to affect the whole preparations (Karimzadegan-Nia et For most patients recurrent or chronic of the nail. As approximately 50% of nail al, 2007; Lawry et al, 2000; Weinberg FFI is more of an inconvenience than dystrophies are due to other causes, it et al, 2005). However, the PAS stain is a problem. Rarely is treatment sought, is important to consider the typical nail a more costly technique (at roughly particularly as there are few symptoms changes which may raise suspicion of double the price of a standard KOH for the sufferer and hence this may onychomycosis (Table 2). As nail infection test). One study has evaluated the explain the high prevalence of the disease. is virtually always a secondary event to cost-effectiveness of the PAS stain Onychomycosis occurs in a subset of skin infection, any patient with toenail and, despite its high sensitivity, it was patients and may lead to thickening and onychomycosis should have their feet not shown to be more cost-effective discolouration of the toe nails. Not only examined for evidence of the primary (Lilly et al, 2006). However, it has does this lead to embarrassment for the source, usually the plantar surface (Daniel been suggested that this test may patient (Turner and Testa,