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- Pitted keratolysis (PK) is a bacterial dermatosis involving the keratin-rich, weight-bearing areas of the feet and, less commonly, the palms.
- It is characterized by both a foul odor and pitting of the stratum corneum that results from bacterial degradation of keratin in affected sites.
- Synonyms: keratoma plantare sulcatum, keratolysis sulcata, ringed keratolysis, and keratolysis plantare sulcatum (1)
- Also known as the “sweaty sock syndrome” (2)
- Treatments include topical and systemic preparations as well as preventative measures; all aimed at reducing bacterial overgrowth, which is the underlying cause of this condition.
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.
- 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.
- 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 produce 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.
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.
- 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.
- 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.