Pitted keratolysis: a case report and review of current literature

Abstract

The article offers a brief history of pitted keratolysis (PK), research regarding PK etiology, evaluation of PK, and current treatment modalities. The main objective of this article focuses on the current literature on PK, its presentation and symptomatology, prevalence, and available therapeutic options. We present a case report and review on PK of a patient treated with an over the counter antiperspirant, topical erythromycin, oral erythromycin, and proper education on hygiene, with complete resolution and without recurrence after a follow up of greater than 12 months.

Introduction

Originally known as keratolysis plantare sulcatum, pitted keratolysis (PK) was first reported and described by Castellani in 1910. ¹ A frustrating, often embarrassing dermatological manifestation for patients, PK is characterized as superficial multifocal, pitted, crater-like erosions, ranging from 1 to 7 mm distributed along the weight-bearing surfaces of the foot.^2,3 These reported yellow or brown lesions may become exudative, with a mildly burning sensation on the plantar soles. Utilizing a Wood’s lamp during clinical evaluation of the pitted lesions generally does not reveal fluorescence. ² Dermoscopy of PK may reveal black pits in a parallel pattern on the ridges of the stratum corneum. ⁴ Patients typically endorse fetor and gross appearance as their main complaint. Aside from malodor and unpleasant morphology reported by patients, PK is relatively asymptomatic on presentation. It has been documented to be highly linked with plantar hyperhidrosis,^1,5 with males being typically more affected than females at a ratio of three to two, respectively. PK occurs more commonly among barefooted laborers, farmers, sailors, soldiers, and industrial workers, most of whom relate prolonged occlusive foot wear. ¹

Available literature on PK was generally of low level studies, with primary focuses on topical antibiotics or antifungal treatment. Topical therapeutics that have been listed in the literature include but are not limited to benzoyl peroxide, clindamycin, erythromycin, gentamycin and tetracycline cream, fusidic acid, mupirocin, and botulinum toxin.^1,3,6,7 Often, hygienic management and education are implemented adjunctively with topical antibiotic treatment for PK. No consensus is reached on the standard treatment of PK from available medical literature.

We present a case report and review on PK. The patient was treated with a multimodal therapeutic approach, which consisted of an over the counter antiperspirant, topical erythromycin, oral erythromycin, and proper education on hygiene.

Case presentation

A 35-year-old male patient serving in the military presented to clinic with longstanding, burning irritation of bilateral plantar feet. He had seen multiple physicians and was previously prescribed different antifungal treatments over several years without improvement. The patient’s past medical history was unremarkable. On physical examination, diffuse maceration of the skin consistent with hyperhidrosis and areas of pitting of the skin on the plantar weight-bearing surfaces were appreciated (Figure 1). Definitive diagnoses of PK and hyperhidrosis were made, and the patient was subsequently treated for both conditions concomitantly. Our patient was instructed to apply an over-the-counter aluminum chloride antiperspirant daily for a week to treat the hyperhidrosis and transition to a one time weekly application as the condition improves. He was additionally directed to take oral erythromycin 500 mg for every six hours and apply topical erythromycin 2% gel twice daily. Within a few days, the oral erythromycin was discontinued due to gastrointestinal intolerance. The patient was instructed to continue with topical erythromycin. After four weeks, the patient’s burning irritation, along with associated skin appearance and symptomatology had completely resolved (Figure 2). The patient followed up at 13 months, with complete resolution and without recurrence. He continued to treat his plantar hyperhidrosis once weekly with aluminum chloride.

Figure 1.

Patient on initial encounter. Note the yellow-brown crater like and pitted erosions on the weight-bearing regions of the plantar surface.

Figure 2.

Patient at 4 weeks, on his sequential encounter. Note the complete resolution of lesions on the plantar weight-bearing surfaces of the right foot.

Discussion

This case report highlights a dermatological pedal presentation that physicians should be made aware of. With careful history taking, physical examination and shoe gear assessment, the physician can appropriately diagnose plantar PK. Descriptors from the patient’s experience including burning, sliminess, itchiness, and soreness can be quite nonspecific. However, recognition of the distinctive malodor, yellow or brown pitted gross appearance of the lesions, excessive plantar sweating, and prolonged use of occlusive shoes upon physical examination is sine qua non for the diagnosis of PK. ³ Without thorough evaluation, PK can easily be misdiagnosed as dermatophytosis, verruca pedis, or erythrasma.

Takama et al. reported hyperhidrosis and malodor as the most frequently observed symptoms in their case series of 53 patients. ³ Hyperhidrosis affects approximately 3% of the general population, occurring at high density regions of eccrine sweat glands. ⁸ Longshaw et al. attributed the production of sulfides, thiols, and thioesters by Kytococcus sedentarius as the source of malodor in PK; ⁹ the extracellular enzymes released by this species are responsible for the degradation of keratin, additionally giving its characteristic pitted appearance. Other Gram-positive bacteria that have been identified in cultured stratum corneum of patients affected by PK include Corynebacterium species, Dermatophilus congolensis, and Streptomyces. ² Clindamycin, benzoyl peroxide, salicylic acid, sulfur, clotrimazole, antibacterial soaps, neomycin, erythromycin, mupirocin, and imidazoles have all been reported by Vlahovic et al. as treatment options with limited efficacies. ² In a case control study of 387 patients, Walling reported plantar hyperhidrosis substantially increasing the risk of cutaneous infections caused by bacterial, fungal, and viral pathogens. ⁵ The odds risk of developing PK with plantar hyperhidrosis was 15.4 with a 95% confidence interval.

In our case presentation, the patient had strict dress code requirements to don military boots for work. With consideration to the lifestyle of the patient as part of the treatment plan, we prescribed aluminum chloride antiperspirant for treatment of his unrelenting hyperhidrosis. If left untreated, the moist micro-environment of the stratum corneum ridges provides rich sustenance to potential infective agents, such as bacteria, fungi, and viruses.^2,8 Fungal scrapings to rule out a concomitant infection were not performed for this patient, as the multiple previous treatments of antifungals were futile. Additionally, fungal cultures have been reported to have low sensitivities. ¹⁰ A study by Flanagan and Glaser demonstrated that aluminum chloride solution of 15% or higher usually takes approximately a week of nightly use to stop sweating, ¹¹ with one or two nightly applications per week thereafter to maintain results for moderate to severe axillary hyperhidrosis. The senior author has previously utilized this regimen for plantar hyperhidrosis with reproducible success, as in the study performed by Flanagan and Glaser. ¹¹ Treating the underlying plantar hyperhidrosis enabled the synergistic management of the cutaneous infection with topical antibiotics. Topical 2% erythromycin gel inhibited bacterial protein synthesis, and secondarily prevented the continued keratin degradation via keratolytic enzymes. Within four weeks of follow-up, the patient demonstrated complete clinical resolution of his plantar lesions.

This case report demonstrates that proper clinical diagnosis of PK, patient education about plantar hyperhidrosis with hygiene maintenance, and appropriate treatment with a topical antibiotic and an antiperspirant provided complete resolution. By managing the underlying aggravating factor of PK, hyperhidrosis, the treating physician can play an important role in preventing further infectious complications. We recommend concomitantly modifying hygienic practices, which include encouraging using breathable, mesh upper soled athletic shoes, avoiding cotton socks and barefoot walking, washing and drying feet daily, applying drying foot powders, and changing out socks daily. Albeit absorbent, cotton socks perform poorly at moisture wicking from skin. ¹² The authors recommend well-padded acrylic based socks, which perform better at moisture wicking from the skin when compared to cotton socks, as reported by Herring and Richie. ¹² Talcum powder has also been reported in the literature in addition to aluminum chloride as a drying agent for the plantar soles. Moreover, plantar hyperhidrosis can be clinically managed by iontophoresis, botulinum toxin injections, or oral glycopyrrolate, if first line treatment of using antiperspirants is ineffective.^8,13 Obtaining a skin shave biopsy and swab cultures can be helpful in ruling out other cutaneous infections. However, organisms have been reported in the literature to be non-specific. ⁷ We therefore highlight the presentation of PK as a clinical diagnosis, which does not necessitate obtaining biopsies, bacterial cultures, nor fungal scrapings on clinical presentation. As such, we believe that a broad spectrum topical antibiotic that targets Gram-positive and Gram-negative bacteria, such as erythromycin, is efficacious in PK treatment. Recognizing PK lesions early saves time and resources, which also improves the patient’s quality of life, illustrated by this case report. Further research involving higher levels of evidence will aid in the standard treatment of PK.