1. What essential question does one still need to help make the diagnosis?
2. What is the tentative diagnosis?
3. Can you list at least three differential diagnoses?
4. What features in this condition differentiate it from other conditions?
5. What is the suitable treatment of this condition?
A 27-year-old Caucasian male presents with a history of a strong smell of the feet for the past five years. He is very active in sports. The patient says he has to replace his shoes every three months and that his family and friends are always aware of the smell.
The patient notes that his feet are becoming a nuisance. He also says his hands and feet sweat a lot. The patient has been aware of scaling on his feet for five years but denies any pain related to the feet. He also denies any pruritus. The patient denies any systemic history at this time. He notes that the pits are more noticeable after he swims or gets out of the shower.
The patient has not seen any health care providers for the condition but has used OTC powders and antifungal medications with no lasting result.
During the clinical examination, I noted symmetric plantar lesions/pits on both feet, including the heels, metatarsal areas and the plantar aspect of the hallux. Many small craterform crypts on the heels coalesced to form larger erosions on both feet.
The pits appear to be between 2 mm to 3 mm in size. The lesions had a white-yellowish appearance and an unpleasant odor. There was some involvement of the posterior aspect of the heel as well as the ball of the foot. The arches and sides of the feet were spared.
I did not note any scales, erythema or tenderness. There was no toenail involvement. A potassium hydroxide (KOH) test of the lesion was negative for hyphae but  an aerobic bacterial swab was positive for Corynebacterium species. A Wood’s lamp examination was also negative.
1. Does the patient’s skin feel slimy or do his socks stick to his skin?
2. Pitted keratolysis
3. Hyperhidrosis, erythrasma and superficial candidiasis
4. Discrete shallow circular lesions with a punched out appearance
5. Keeping feet dry and using topical antibacterials
Pitted keratolysis (PK), originally called “keratoma plantare sulcatum” by Castellani in 1910, first presented in those who went barefoot during the rainy season in tropical areas.1 Acton and McGuire renamed the disease “keratolysis plantare sulcatum” since the condition is actually a partial loss of the stratum corneum rather than a hyperkeratosis as Castellani’s “keratoma” implied. 2 We see it mostly in athletes who spend prolonged times in occlusive footwear or in those who work in very wet environments.
Sulfur containing compounds produced by the bacteria lead to the malodor. The pungent odor has lead to a new name of “toxic sock syndrome.” 3
Pitted keratolysis is caused by a cutaneous infection with either Micrococcus sedentarius (now renamed as Kytococcus sedentarius), Dermatophilus congolensis and the Corynebacterium species. 4 Other organisms that can cause this infection include Actinomycetes keratolytica and Streptomyces.
These superficial bacterial “infections” occur in the stratum corneum and are associated with overgrowth of normal flora at sites of occlusion and high surface humidity. They are non-inflammatory in appearance. 4
The human skin harbors a complex microbial ecosystem with transient, short-term resident and long-term resident biota, based on the consistency with which they are isolated. Staphylococcus, Micrococcus, Corynebacterium, Brevibacteria, Propionibacteria and Acinetobacter species, among others, are regularly cultivated from normal skin. 5
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
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.
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.
Hyperhidrosis. Unlike pitted keratolysis, hyperhidrosis is not a temporary condition. It must commonly occurs in the hands, armpits and feet. In these cases the most likely explanation is a genetic trait. 10
The eccrine sweat glands are mainly concentrated in the palms of the hands and soles of the feet. These patients will sweat all of the time and occlusive footwear or wet environments are not a factor.
Erythrasma. This superficial localized chronic skin infection is caused by Corynebacterium minutissimum. It presents where there are moist occluded intertriginous areas and frequently presents as asymptomatic chronic maceration with fissuring or scaling.
Predisposing factors include: humid climate, poor hygiene, hyperhidrosis, obesity, diabetes, advanced age and an immunocompromised host. In some patients, this condition presents as a hyperkeratotic, white macerated plaque, especially in the fourth interspace. 1 There is no central clearing as one would see with tinea pedis.
The most common site of involvement is the toe web spaces. When there is accompanying pruritus, irritation of lesions may cause secondary changes of excoriations and lichenification. In other areas, the lesions present as pink to red. One may notice that the lesions are covered with fine scales and they may be accompanied by fine wrinkling. The red color fades to brown. Wood’s lamp shows coral red fluorescence caused by coproporphyrin III. 11
Superficial cutaneous candidiasis. This condition occurs more often in immunocompromised people and involves the very outermost layers of the skin. Healthy skin is quite resistant to candidal infection. Pruritus and irritation of the affected areas are the usual complaints. 12
Dyshidrotic eczema. Also called dyshidrosis or pompholyx, dyshidrotic eczema is an intensely pruritic condition that affects the hands more often than the feet and the sides of the digits are more characteristically affected. It is characterized by the development of vesicular eruptions along the sides of the extremities or digits, and between the digits. Interdigital maceration and desquamation of the interdigital spaces often are present. 13
In some patients, dyshidrotic eczema presents as symmetric crops of clear vesicles and/or bullae on the soles and the lateral aspects of toes. Many cases of dyshidrotic eczema are the result of an occult allergen causing an allergic contact dermatitis. 14
Pseudomonal pyoderma. This superficial infection of the skin has a bluish-green purulence, a “grape juice” aromatic odor and a moth eaten appearance of the epidermis with macerated borders. It presents in the toe webs.
Palmoplantar punctate keratoderma. With this condition, there is obvious thickening of the stratum corneum with scaling. This condition is usually inherited but it can be acquired. One may sometimes see hyperkeratosis with this condition. There is no associated infection of the skin.
Basal cell nevus syndrome. This is an inherited disorder characterized by wide-set eyes, saddle nose, frontal bossing (prominent forehead), prognathism (prominent chin), numerous basal cell carcinomas and skeletal abnormalities. Skin manifestations include pits in the palms and soles as well as numerous basal cell carcinomas. 15
Less common considerations in the differential diagnosis include porokeratosis, arsenic keratosis, tungiasis, yaws and keratolysis exfoliativa. 2
Treatment for pitted keratolysis involves keeping the feet as dry as possible because excessive moisture is what triggers this condition. Inert powders such as Desenex (Novartis) and Zeasorb (Stiefel) can help but are not as effective as aluminum chloride 20% solution. Drysol is one such agent that is 25% aluminum chloride and is readily available.
Since the condition is due to an overproduction of bacterial organisms, the use of topical antibacterials is common. This includes topical erythromycin (Eli Lilly), clindamycin gels (Cleocin, Pfizer) applied twice daily or clindamycin phosphate solution administered bid for 10 days.
Gels seem to be somewhat more effective than lotions but may be significantly more irritating if the inflammation and pitting are particularly severe. Physicians have used several acne medications such as benzoyl peroxide as well. 3 Other topical applications include mupirocin (Bactroban, GlaxoSmithKline) and clotrimazole (Lotrimin, Schering-Plough) or Mycelex, Bayer).
For patients with severe cases, one may commonly use oral antibiotics. I prefer to use erythromycin 333 mg TID for 10 days. Others recommend oral Cleocin.
As with all cases of pitted keratolysis, patients should always wear boots or shoes for a short time and wear socks at all times. They should also wash their feet with soap twice a day and not wear the same shoes two days in a row.
Dr. Morse is the President of the American Society of Podiatric Dermatology. He is a Fellow of the American College of Foot and Ankle Surgeons, and the American College of Foot and Ankle Orthopedics and Medicine. Dr. Morse is board certified in foot surgery.
For further reading, see “How To Handle Common Skin Dermatoses” in the September 2002 issue of Podiatry Today.
To check out the archives and get reprint information, visit www.podiatrytoday.com.
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