When A Patient Presents With Malodorous, Macerated Feet
Depending on personal hygiene and the immediate environmental conditions, superficial layers of the skin contain many dead cells where colonies of Staphylococcus epidermidis, Streptococcus and gram-negative bacilli known as diphtheroids inhabit. Most pathogenic bacteria are unable to survive on clean, healthy skin because of the acid pH of the skin. 6
All of these bacteria share common features, which enable them to produce keratin degrading serum proteinases, known as exoenzymes (keratinase) that destroy the stratum corneum and open small tunnels and pits. 4 These bacteria produce porphyrins that reveal bright coral pink fluorescence in the pits under a Wood’s light, which confirms the diagnosis. 7
The Corynebacteria are a diverse group of gram-positive, non-sporing rod-shaped organisms that include Corynebacterium diphtheriae. These organisms are usually referred to as diphtheroids or coryneforms. It is similar to Staphylococcus.
Three skin conditions appear to be related to an overabundance of these coryneforms. These conditions include pitted keratolysis, erythrasma and trichomycosis. 2 Micrococcus sedentarius is a gram-positive Staphylococcus-related bacteria that invades the softened stratum corneum. Dermatophilus congolensis is a gram-positive facultative anaerobic bacteria.
Pitted keratolysis occurs in adults and children, and is more common in adult males with sweaty feet. Sliminess of the skin and socks sticking to feet are common complaints. The condition is malodorous 89 percent of the time and pruritic 8 percent of the time. Hyperhidrosis is the most frequently observed symptom of this condition.
In regard to laboratory identification, the organisms are not easy to find in KOH mounts but gram-stained scrapings can more easily detect them. To confirm pitted keratolysis, one should use an aerobic swab and put the skin scrapings in the tube for an aerobic culture. The organisms appear as coccoid and filamentous forms with branches and septa. Periodic acid-Schiff (PAS) mounts may sometimes show the organism. 8
The infection appears as numerous superficial erosions of the horny layer of the soles and undersurface of the toes. Discrete shallow circular lesions with a punched out appearance coalesce to produce irregular erosions. Occasionally, there can be green or brown discoloration, depending on the species of the organism.
The most common sites for the onset of pitted keratolysis are the pressure-bearing areas, such as the ventral aspect of the toe, the ball of the foot and the heel. The next most common site is a friction area, the interface of the toes. It is rare to see these lesions on the non-pressure-bearing locations. 9
Pearls On Diagnosing Pitted Keratolysis
A false negative result may occur if the patient has recently washed his or her feet. For this reason, a late afternoon examination of the feet may be the most revealing. The appearance is more dramatic if the feet are wet. The predisposing factors are hyperhidrosis, prolonged occlusion and increased skin surface pH.
One normally finds small crater-like depressions on weightbearing regions of the soles. Either the forefoot or the heel can become infected. There is no evidence of erythema or inflammation, and the disease often goes unnoticed by the patient. 4 There is no fluorescence on examination with a Wood’s light. If one elects to do a biopsy, a shave biopsy is more helpful than a punch biopsy. Physicians rarely obtain biopsies for pitted keratolysis.
Hyperhidrosis is often associated with maceration and a foul odor. If you are unsure of the diagnosis, soak the foot in water for 15 minutes. This causes swelling of the horny layer and accentuates the lesions.
A Guide To The Differential Diagnosis
Conditions commonly included in the differential diagnosis are plantar warts and tinea pedis. Plantar warts typically have localized areas of hyperkeratosis and are often painful whereas athlete’s foot presents as pruritus between the toes and is not limited to pressure-bearing areas. 2 It is helpful to assess the condition of the nails. If there is onychomycosis present, tinea pedis is usually present as well.