What is pitted keratolysis?
Pitted keratolysis, also known as keratolysis plantare sulcatum or ringed keratolysis, is a superficial bacterial skin infection characterised by crater-like pits and malodour. It typically affects pressure-bearing areas on the soles of the feet, although the palms are rarely affected.
This condition is very treatable with a good prognosis.
Pitted keratolysis
Who gets pitted keratolysis?
Pitted keratolysis is more commonly seen in men compared to women and can affect all age groups.
Occupations at risk include:
- Athletes
- Industrial workers
- Miners
- Farmers
- Sailors and fishermen
- Military workers
- Occupations where feet are constantly wet (paddy field workers, boatmen).
Factors that increase the risk of developing pitted keratolysis include:
- Hyperhidrosis — excessive sweating of the hands and feet
- Keratoderma — thickened skin of palms and soles
- Prolonged use of occlusive footwear (vinyl footwear, rubber boots)
- Diabetes mellitus
- Poor foot hygiene
- Hot humid weather
- Obesity
- Immunodeficiency.
What causes pitted keratolysis?
Pitted keratolysis is caused by a range of bacterial species. The most common are Corynebacteria, Dermatophilus congolensis, Kytococcus sedentarius, Actinomyces, or Streptomyces.
Bacteria thrive under moist and warm conditions. They proliferate and produce protease enzymes that cause destruction of the stratum corneum to create pits/craters. The odour is associated with the sulfur compounds (thiols, sulphides, and thioesters) which are produced by the bacteria.
What are the clinical features of pitted keratolysis?
The infection often occurs bilaterally on pressure-bearing areas, most commonly the ball of the foot and heel. Involvement of the palms have been reported in certain professions such as rice paddy farmers.
It is often asymptomatic, however, when symptomatic there may be associated pruritus and pain on walking.
Characteristic features include:
- Pits on the stratum corneum (1–3mm); these may form confluences, irregular erosions, or sulci
- Some pits may have a brown appearance (giving the appearance of dirty feet)
- The appearance of the pits are often amplified when feet are wet.
Associated features:
- Hyperhidrosis
- Slimy texture of the skin
- Malodorous feet.
Variants of pitted keratolysis (less common):
- Painful plaque-like variant: tender erythematous to violaceous papules
- Large crateriform depressions
- Corynebacterial triad: pitted keratolysis, erythrasma, and trichomycosis axillaris.
How do clinical features vary in differing types of skin?
Pitted keratolysis has been seen in patients of all skin types. They all present similarly and can present in a range of sizes and colours.
What are the complications of pitted keratolysis?
- Psychosocial impact due to foot odour
- Limitation of function due to symptomatic pitted keratolysis
No mortality is associated with pitted keratolysis.
How is pitted keratolysis diagnosed?
Diagnosis is often clinical given its distinctive appearance and malodour. Consider examination of intertriginous areas (axilla and groin) for co-existing corynebacterial infections, such as erythrasma and trichomycosis axillaris.
Other investigations that can be considered:
- Wood lamp examination which shows coral red fluorescence (erythrasma)
- Skin scrapings may be taken to exclude a fungal infection
- Skin biopsy if there is diagnostic uncertainty, with histopathology revealing:
- Pits or erosions limited to stratum corneum
- Microorganisms with coccoid or filamentous forms may be detected on stain
- Culture rarely indicated but may identify the causative organism.
What is the differential diagnosis for pitted keratolysis?
- Basal cell nevus syndrome
- Focal acral hyperkeratosis
- Keratolysis exfoliativa
- Plantar warts
- Tinea pedis
What is the treatment for pitted keratolysis?
Pitted keratolysis can be treated successfully with adequate foot hygiene, topical antibiotics, and antiseptics.
General measures
- Ensure adequate foot hygiene:
- Avoid prolonged use of occlusive footwear
- Wear properly fitted footwear to reduce foot friction
- Wear absorbent cotton socks and ensure frequent changing of socks
- Wash socks after wear at 60°C with soap and water to eliminate bacteria
- Wash feet with soap or antiseptic cleanser twice a day
- Apply antiperspirant to the feet regularly
- Avoid sharing footwear with others.
- Rotate dry insoles on a daily basis so feet are never standing on damp shoe inners
- Manage underlying hyperhidrosis.
Specific measures
Topical antibiotics
- Commonly used options applied twice daily, usually for 2–4 weeks are:
Other agents
- Benzoyl peroxide
- Antimicrobial with keratolytic properties
- Can be used alone or in combination with other topical antibiotics
Oral antibiotics (for refractory disease)
- Clindamycin or erythromycin
- Duration dependent on severity and response to treatment, at least 10 days recommended
- Tetracyclines are an alternative
What is the outcome for pitted keratolysis?
Pitted keratolysis is treatable and has an excellent prognosis.
- No treatment: may last for years with spontaneous remission or exacerbation.
- With treatment: often resolves in 2–4 weeks.