para>Primary care providers or pharmacists who lack an understanding of PK may erroneously attribute patient symptoms to mycotic infection, resulting in ineffective treatment regimens and perpetual infection. ‚
EPIDEMIOLOGY
- Both males and females affected, but most patients seem to be males; male prevalence might be related to hygiene and occlusive footwear (3).
- Patients tend to be young, with a mean age of 24.9 years, but a range between 10 and 57 years.
- No race predilection exists for PK.
Prevalence
- PK is likely a common problem, although sparse epidemiologic data include general prevalence rates of only 0.48 " “2.6%.
- Occurs worldwide; affects barefooted populations in tropical environments and those with occlusive footwear especially in temperate regions (1,3).
- International incidence rates of PK vary significantly according to occupation and sports activity; prevalence of 1.5% in Korean industrial workers to 42.5% in South Indian paddy field workers (3).
- Studies of specific populations at risk such as athletes, soldiers in tropical climates, or the homeless show prevalence to be 13.6%, 53%, and 20.4%, respectively.
- This condition, which is often painless and can be embarrassing to patients, is thought to be significantly underreported.
ETIOLOGY AND PATHOPHYSIOLOGY
- Causative agents include gram-positive organisms: Corynebacterium species, Kytococcus sedentarius, Dermatophilus congolensis, and Actinomyces keratolytica (3).
- These bacteria produce keratolytic enzymes that dissolve the stratum corneum producing craterlike pits on the sole of the foot.
- Sulfur by-products of these proteolytic enzymes produces the foul odor.
- Unlike infections caused by extrinsic organisms, such as tinea pedis, PK results from overgrowth of the patient 's own skin flora under the influence of high moisture, high pH, and poor hygiene.
Genetics
The finding in one study that PK does occur in members of the same family suggests the influence of genetics and/or similar hygienic conditions. ‚
RISK FACTORS
- Overgrowth of bacteria that cause PK is favored by high moisture, high pH, and poor hygiene.
- Primary hyperhidrosis, which affects 3% of the population, is the predisposing factor for bacterial proliferation. Conditions for bacterial overgrowth are most likely to be caused by prolonged wearing of occlusive footwear associated with athletics, civilian occupations that require foot protection, and the military.
GENERAL PREVENTION
- Prevention strategies revolve around avoiding conditions that are hospitable to causative organisms.
- In particular, regular foot washing and avoidance of prolonged wearing of occlusive footwear, as well as wearing moisture-wicking synthetic socks and changing socks frequently (2); synthetic socks are preferred to cotton socks which tend to retain moisture.
- Those who have hyperhidrosis, in addition to taking the above precautions, can prevent PK by treating their underlying condition.
COMMONLY ASSOCIATED CONDITIONS
- Other skin infections caused by Corynebacterium include erythrasma (a superficial dermatosis known for its coral red fluorescence under Wood lamp examination) and trichomycosis (an infection involving hair shafts, which tends to occur in humid environments) may exist concurrently with PK (<10%).
- Warm, moist, and occlusive environments are associated both with bacterial infections, such as PK, and with viral infections, such as plantar warts, and with fungal infections, such as tinea pedis.
DIAGNOSIS
HISTORY
- Patients with PK are likely to complain of pitting on the soles of their feet and the embarrassing foul odor that usually accompanies the condition.
- It should be noted, however, that in about 10 " “20% of patients, perhaps due to different flora or hygienic practices, there is no complaint of malodor.
- Up to 50% of patients report pain, burning, or irritation, which can be more severe after periods of prolonged occlusion.
- Patients may also complain that their skin is excessively sweaty, which may be due to primary hyperhidrosis, secondary hyperhidrosis (e.g., anxiety, hyperthyroidism), or environmental conditions produced by footwear required for occupational or recreational activities.
PHYSICAL EXAM
- PK typically involves pressure-bearing, keratin-rich areas of the feet, including the ball, heel, and the ventral aspect of the toe.
- Pitted lesions are usually discrete, flesh-colored, circular, and shallow, but may coalesce to larger craterlike structures; usually 1 to 7 mm diameter and 1 to 2 mm in depth.
- Pits may be more prominent when feet are water soaked (2,4).
- In addition to being pitted, lesions can be annular, erythematous instead of flesh-colored, plaque-like, macerated, or fissured.
- Malodor may or may not be present at the time of examination.
DIFFERENTIAL DIAGNOSIS
- The most common conditions to be confused with PK are tinea pedis and plantar warts.
- Tinea pedis often presents with pruritus and usually affects the keratin-poor interdigital areas.
- Plantar warts typically have localized areas of hyperkeratosis and are often consistently painful during weight-bearing activities.
- Less common considerations in the differential diagnosis include punctate hyperkeratosis, porokeratosis, basal cell nevus syndrome, arsenic keratosis, tungiasis, yaws, and keratolysis exfoliativa.
- These conditions, and the dermatology/dermatopathology consultation likely needed to diagnose them, should be considered in apparent cases of PK that are resistant to treatment.
DIAGNOSTIC TESTS & INTERPRETATION
- History and physical exam are often pathognomonic.
- Additional lab testing, bacterial cultures, or biopsy may be performed in resistant cases or where other diagnoses are being considered.
TREATMENT
GENERAL MEASURES
- Avoid wearing occlusive footwear, if possible.
- Keep feet clean and dry; wash feet twice daily with soap or antibacterial cleanser.
- Avoid ill-fitting shoes in an effort to reduce friction and callous formation (1)[C].
- Wear moisture-wicking synthetic socks (5)[C]. Contrary to popular belief, cotton and wool socks retain moisture more than socks composed of synthetic materials.
MEDICATION
First Line
- Topical antibiotics, including erythromycin 2% and clindamycin 1% applied twice daily.
- Topical antibiotics are well accepted and easy to apply.
- Topical erythromycin clears lesions in 2 to 3 weeks (3).
Second Line
- Topical 5% benzoyl peroxide has antibacterial and keratolytic properties; keratolytic properties enhance skin penetration.
- In a study of 44 patients, topical clindamycin, benzoyl peroxide, or the combination of these two agents were all found to be equally effective. Given these results, consider reserving combination topical therapy for resistant cases.
- When topical antibiotic therapies fail, systemic therapies, such as oral erythromycin, can be tried.
- No evidence to support the use of systemic antibiotics; oral antibiotics are also unlikely to reach stratum corneum where bacteria lie (1).
ADDITIONAL THERAPIES
- Other treatments involve topical mupirocin or topical fusidic acid; fusidic acid is not available in the United States; fusidic acid is preferred over mupirocin (1).
- In cases where the patient is not able to keep the feet dry, either due to the requirement of occlusive footwear or primary hyperhidrosis, topical 20% aluminum chloride solution applied twice daily can be used.
- Antiperspirants block hyperactive sweat glands so temporarily reduce sweating; note that antiperspirants, not deodorants should be employed (1).
SURGERY/OTHER PROCEDURES
In patients resistant to topical and systemic antibiotics, subcutaneous injection of low dose botulism toxin into the plantar region has resulted in cure; it is expensive and uncomfortable for the patient so it should be reserved to those unresponsive to more traditional therapies (1). ‚
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
- With the above treatments, most cases resolve within about 3 weeks.
- In resistant cases, second-line treatments and more concerted efforts at moisture reduction and/or dermatologic referral should be considered.
PATIENT EDUCATION
- Emphasize the importance of keeping feet clean and dry.
- Recommend synthetic socks over cotton or wool socks.
- Encourage follow-up if symptoms do not resolve within 3 to 4 weeks.
PROGNOSIS
Excellent ‚
REFERENCES
11 Bristow ‚ IR, Lee ‚ YL. Pitted keratolysis: a clinical review. J Am Podiatr Med Assoc. 2014;104(2):177 " “182.22 Tlougan ‚ BE, Mancini ‚ AJ, Mandell ‚ JA, et al. Skin conditions in figure skaters, ice-hockey players and speed skaters: part II " “cold-induced, infectious and inflammatory dermatoses. Sports Med. 2011;41(11):967 " “984.33 Pranteda ‚ G, Carlesimo ‚ M, Pranteda ‚ G, et al. Pitted keratolysis, erythromycin, and hyperhidrosis. Dermatol Ther. 2014;27(2):101 " “104.44 van der Snoek ‚ EM, Ekkelenkamp ‚ MB, Suykerbuyk ‚ JC. Pitted keratolysis; physicians ' treatment and their perceptions in Dutch army personnel. J Eur Acad Dermatol Venereol. 2013;27(9):1120 " “1126.55 Sedgwick ‚ PE, Dexter ‚ WW, Smith ‚ CT. Bacterial dermatoses in sports. Clin Sports Med. 2007;26(3):383 " “396.
ADDITIONAL READING
- Blaise ‚ G, Nikkels ‚ AF, Hermanns-L ƒ ª ‚ T, et al. Corynebacterium-associated skin infections. Int J Dermatol. 2008;47(9):884 " “890.
- De Luca ‚ JF, Adams ‚ BB, Yosipovitch ‚ G. Skin manifestations of athletes competing in the summer olympics: what a sports medicine physician should know. Sports Med. 2012;42(5):399 " “413.
- Kim ‚ BJ, Park ‚ KU, Kim ‚ JY, et al. Comparative study of benzoyl peroxide versus clindamycin phosphate in treatment of pitted keratolysis. Korean J Med Mycol. 2005;10:144 " “150.
- Morais ‚ P, Peralta ‚ L. Smelly foot rash. Aust Fam Physician. 2011;40(3):123 " “124.
- Singh ‚ G, Naik ‚ CL. Pitted keratolysis. Indian J Dermatol Venereol Leprol. 2005;71(3):213 " “215.
- Tamura ‚ BM, Cuce ‚ LC, Souza ‚ RL, et al. Plantar hyperhidrosis and pitted keratolysis treated with botulinum toxin injection. Dermatol Surg. 2004;30(12, Pt 2):1510 " “1514.
- Walling ‚ HW. Primary hyperhidrosis increases the risk of cutaneous infection: a case-control study of 387 patients. J Am Acad Dermatol. 2009;61(2):242 " “246.
CODES
ICD10
L08.89 Oth local infections of the skin and subcutaneous tissue ‚
ICD9
686.8 Other specified local infections of skin and subcutaneous tissue ‚
SNOMED
Pitted keratolysis ‚
CLINICAL PEARLS
- Patients with PK are likely to complain of pitting on the soles of their feet and of the embarrassing foul odor that usually accompanies the condition.
- The most common conditions to be confused with PK are tinea pedis and plantar warts.
- Treatment with topical antibiotic agents seems successful but is based on limited evidence.
- Controlling hyperhidrosis is key to treatment.