Pitted keratolysis (also known as Keratolysis plantare sulcatum,
Keratoma plantare sulcatum,
and Ringed keratolysis
) is a bacterial
skin infection
A skin infection is an infection of the skin in humans and other animals, that can also affect the associated soft tissues such as loose connective tissue and mucous membranes. They comprise a category of infections termed skin and skin structure ...
of the foot.
The infection is characterized by craterlike pits on the sole of the feet and toes, particularly
weight bearing In orthopedics, weight-bearing is the amount of weight a patient puts on an injured body part. Generally, it refers to a leg, ankle or foot that has been fractured or upon which surgery has been performed, but the term can also be used to refer to r ...
areas.
The infection is caused by ''
Corynebacterium
''Corynebacterium'' () is a genus of Gram-positive bacteria and most are aerobe, aerobic. They are bacillus (shape), bacilli (rod-shaped), and in some phases of life they are, more specifically, club (weapon), club-shaped, which inspired the gen ...
'' species
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and ''
Kytococcus sedentarius''.
Excessive sweating
Hyperhidrosis is a condition characterized by abnormally increased sweating, in excess of that required for regulation of body temperature. Although primarily a benign physical burden, hyperhidrosis can deteriorate quality of life from a psychologi ...
of the feet and use of occlusive footwear provide an environment in which these bacteria thrive and therefore increase the risk of developing pitted keratolysis.
The condition is fairly common, especially in the military where wet shoes/boots are worn for extended periods of time without removing/cleaning. Skin biopsy specimens are not usually utilized, as the diagnosis of pitted keratolysis is often made by visual examination and recognition of the characteristic odor.
Wood's lamp
A blacklight, also called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and very little visible light. One type of lamp has a violet filter material, either on the bulb or in a separat ...
examination results are inconsistent. Treatment of pitted keratolysis requires the application of
antibiotic
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...
s to the skin such as
benzoyl peroxide
Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide () ...
,
clindamycin
Clindamycin is an antibiotic medication used for the treatment of a number of bacterial infections, including osteomyelitis (bone) or joint infections, pelvic inflammatory disease, strep throat, pneumonia, acute otitis media (middle ear infec ...
,
erythromycin
Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used duri ...
,
fusidic acid, or
mupirocin
Mupirocin, sold under the brand name Bactroban among others, is a topical antibiotic useful against superficial skin infections such as impetigo or folliculitis. It may also be used to get rid of methicillin-resistant ''S. aureus'' (MRSA) when ...
.
Prevention efforts aim to keep the feet dry by using moisture-wicking shoes and socks as well as
antiperspirant
A deodorant is a substance applied to the body to prevent or mask body odor due to bacterial breakdown of perspiration or vaginal secretions, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, prevents s ...
s.
Signs and symptoms
Pitted keratolysis typically presents with white discoloration of the skin and numerous discrete, "punched-out" pitted lesions or erosions, usually located on the soles of the feet.
The pits are typically 1–7 millimeters in diameter.
These circular and shallow pits are characteristic of pitted keratolysis, and often overlap to produce larger areas of erosion. The appearance of this condition’s characteristic lesions becomes more pronounced when the affected area is wet or submerged in water. Occasionally these lesions present with a green or brown hue around and within the pits.
These superficial erosions are found under the toes and on the soles of the feet, and especially at the pressure bearing points such as the heel.
Typically, both feet are equally affected. Rarely, the condition affects the palms.
Cause
The most common cause of pitted keratolysis is ''
Corynebacterium
''Corynebacterium'' () is a genus of Gram-positive bacteria and most are aerobe, aerobic. They are bacillus (shape), bacilli (rod-shaped), and in some phases of life they are, more specifically, club (weapon), club-shaped, which inspired the gen ...
'' species. However, several other bacteria may also cause the condition, particularly ''Actinomyces keratolytica'', ''
Dermatophilus congolensis
''Dermatophilus congolensis'' is a Gram-positive bacterium and the cause of a disease called dermatophilosis (sometimes called mud fever) in animals and humans, a dermatologic condition that manifests as the formation of crusty scabs containing t ...
'', ''
Kytococcus sedentarius'', and ''
Streptomyces
''Streptomyces'' is the largest genus of Actinomycetota and the type genus of the family Streptomycetaceae. Over 500 species of ''Streptomyces'' bacteria have been described. As with the other Actinomycetota, streptomycetes are gram-positive, ...
''.
Less frequently, it is due to ''
Acinetobacter
''Acinetobacter'' is a genus of gram-negative bacteria belonging to the wider class of Gammaproteobacteria. ''Acinetobacter'' species are oxidase-negative, exhibit twitching motility, and occur in pairs under magnification.
They are important ...
'', ''
Clostridium
''Clostridium'' is a genus of anaerobic, Gram-positive bacteria. Species of ''Clostridium'' inhabit soils and the intestinal tract of animals, including humans. This genus includes several significant human pathogens, including the causative ag ...
'', ''
Klebsiella
''Klebsiella'' is a genus of Gram-negative, oxidase-negative, rod-shaped bacteria with a prominent polysaccharide-based capsule.
''Klebsiella'' species are found everywhere in nature. This is thought to be due to distinct sublineages developin ...
'', and ''
Pseudomonas
''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able ...
'' species.
Pathogenesis
Pitted keratolysis is associated with excessive sweating of the palms or soles (
palmoplantar hyperhidrosis
A palmoplantar hyperhidrosis is excessive sweating localized to the palms of the hands and soles of the feet. It is a form of focal hyperhidrosis in that the excessive sweating is limited to a specific region of the body. As with other types of foc ...
.)
The pits seen in pitted keratolysis are caused by bacteria secreting
proteinase
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...
enzymes which cause the breakdown of the
keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s in the
stratum corneum
The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compact ...
layer of the affected skin.
This results in the formation of sulfur compounds which leads to a very strong and foul foot odor.
The bacteria that cause pitted keratolysis thrive in warm and humid environments.
Irritation is generally minimal, though occasionally burning, itching, and soreness are experienced with pitted keratolysis.
Diagnosis
The diagnosis of pitted keratolysis is based primarily on the physical examination, with recognition of the classic pitted lesions and pungent odor. Dermoscopic examination can facilitate visualization of pits and pit walls. A Wood's lamp may show coral red fluorescence, as seen in erythrasma. However, this finding is not uniformly present, as the condition may be caused by bacteria that do not produce fluorescent pigments. Further laboratory testing is not typically required for the diagnosis. However, a potassium hydroxide preparation can help rule out the presence of a fungal infection. Imaging and biopsy are not necessary.
Differential diagnosis
*
Acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
*
Athlete's foot
Athlete's foot, known medically as ''tinea pedis'', is a common skin infection of the feet caused by a fungus. Signs and symptoms often include itching, scaling, cracking and redness. In rare cases the skin may blister. Athlete's foot fungus m ...
(''Tinea pedis'')
*
Erythrasma
Erythrasma is a superficial skin infection that causes brown, scaly skin patches. It is caused by '' Corynebacterium minutissimum'' bacteria, a normal part of skin flora (the microorganisms that are normally present on the skin).
There are two ty ...
*
Hyperhidrosis
Hyperhidrosis is a condition characterized by abnormally increased sweating, in excess of that required for regulation of body temperature. Although primarily a benign physical burden, hyperhidrosis can deteriorate quality of life from a psychologi ...
Treatment
As of 2014, there is little high-quality evidence to provide guidance and support one treatment method over another. Therefore, the optimal treatment approach for pitted keratolysis remains unclear as the condition has not been well-studied.
One review suggested a treatment approach requiring modification of risk factors (e.g., keeping feet clean and dry) and treating the underlying bacterial infection.
Effective antibiotic options include
clindamycin
Clindamycin is an antibiotic medication used for the treatment of a number of bacterial infections, including osteomyelitis (bone) or joint infections, pelvic inflammatory disease, strep throat, pneumonia, acute otitis media (middle ear infec ...
,
erythromycin
Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used duri ...
,
mupirocin
Mupirocin, sold under the brand name Bactroban among others, is a topical antibiotic useful against superficial skin infections such as impetigo or folliculitis. It may also be used to get rid of methicillin-resistant ''S. aureus'' (MRSA) when ...
, and
fusidic acid. Topical clindamycin is generally preferred as the first-line choice due to lower cost and better availability.
Fusidic acid is preferred over mupirocin in most cases due to less resistance to fusidic acid amongst ''
Methicillin-sensitive staphylococcus aureus
''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive ...
'' and ''
Methicillin-resistant staphylococcus aureus
Methicillin-resistant ''Staphylococcus aureus'' (MRSA) is a group of Gram-positive bacteria that are genetically distinct from other strains of ''Staphylococcus aureus''. MRSA is responsible for several difficult-to-treat infections in humans. ...
''.
Benzoyl peroxide
Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide () ...
is an effective alternative over-the-counter option and is thought to be as effective as topical clindamycin.
Clinical cure was typically seen after 2.5–3 weeks.
Oral antibiotics are not typically recommended.
Foot hygiene is important. The feet may be washed at least daily with soap and water, and dried thoroughly afterwards. Moisture-wicking socks and shoes may be worn and
antiperspirant
A deodorant is a substance applied to the body to prevent or mask body odor due to bacterial breakdown of perspiration or vaginal secretions, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, prevents s ...
s, such as
aluminum chlorohydrate
Aluminium chlorohydrate is a group of water-soluble, specific aluminium salts having the general formula Aln Cl(3n-m)( OH)m. It is used in cosmetics as an antiperspirant and as a coagulant in water purification.
In water purification, this compou ...
, may help to keep the feet dry. Injections of
botulinum toxin
Botulinum toxin, or botulinum neurotoxin (BoNT), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromusc ...
have successfully induced cessation of sweating (anhidrosis) of the soles of the feet and led to resolution of pitted keratolysis.
These injections are typically reserved for refractory cases of pitted keratolysis that have failed to respond to environmental modifications and antibiotics due to the high cost and pain associated with botulinum toxin injections.
Pitted keratolysis can be reduced and eventually stopped by regularly applying a liberal amount of antiperspirant body powder to the inside of the shoes and socks of the affected person. Regular powder application will greatly reduce foot perspiration and keep the plantar surface of the foot dry therefore creating an environment hostile to the ''Corynebacterium''.
Epidemiology
Pitted keratolysis occurs worldwide and in various climates. The infection is more common in people who live in tropical climates and walk barefoot, and those who spend a lot of time wearing occlusive footwear (e.g., tight shoes, rubber boots),
such as in the military where wet shoes are worn for a prolonged period of time without removing and proper hygiene.
History
Pitted keratolysis was first named ''keratoma plantare sulcatum''.
See also
*
List of cutaneous conditions
Many skin conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against t ...
References
External links
{{Bacterial cutaneous infections
Bacterium-related cutaneous conditions