Imaging Quiz Answer: A Foot Rash With a Foul Odor
CPT Timothy L. Gardner, MD; LTC Dirk M. Elston, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 2 - FEBRUARY 2021
The dark, moist environment created by athletic shoes and the accompanying friction predispose active patients to certain dermatologic conditions. Friction and maceration can cause blisters and calluses, providing a setting for microbes of various kinds to thrive. The overgrowth of skin flora can produce pitted keratolysis, which was the diagnosis for this patient (figure 2).
DiscussionPitted keratolysis is a superficial infection of the skin with the bacteria Micrococcus sedentarius, Dermatophilus congolensis, or species of Corynebacterium and Actinomyces.(1-3) (See "Pitted Keratolysis: A Common Infection of Active Feet," October 1996.) The most common site for pits to appear is on the weight-bearing surfaces of the feet (4). The palms of the hands can also be affected, but one typically sees scale collarettes rather than pits (5). The infection is most often asymptomatic, but a painful violaceous plaque-like form of pitted keratolysis has been reported (4).
The clinical appearance of the rash with foot odor is usually sufficient to make the diagnosis. Biopsies are generally not required, but are occasionally submitted by clinicians unfamiliar with the condition.
On biopsy, the causative gram-positive organisms are found in the sides and bases of the pits in the stratum corneum (figure 3) (3,6). It appears that the organisms produce proteolytic enzymes that erode the horny layer (3). The odor is believed to come from a mixture of thiols, sulfides, and thioesters (2).
Initial treatment consists of limiting the use of occlusive footwear and reducing friction and moisture. Properly fitted shoes and absorbent cotton socks should be worn. Hyperhydrosis can be a predisposing factor, and a drying agent such as 20% aluminum chloride, 2% buffered glutaraldehyde, or 40% formalin ointment can be used (7-9). Aluminum chloride is the preferred treatment. Since aluminum chloride and other drying agents possess no antibacterial properties, the pitting may remain unless a topical antibiotic is used (7).
A 1-month trial of aluminum chloride is usually adequate, but many clinicians use topical antibiotics as initial therapy because they are less irritating. Effective topical antibiotics include erythromycin, clindamycin phosphate, mupirocin, gentamicin sulfate, and tetracycline hydrochloride (4,5,10,11). Some topical antifungals with gram-positive antibacterial properties (such as miconazole nitrate and clotrimazole) can be used (5). Systemic erythromycin has also been beneficial (4).
With treatment, the odor and pitting resolve within 3 to 4 weeks without sequelae (11). In our patient, treatment consisted of the use of topical erythromycin three times daily, which cleared the lesions and odor in 3 weeks.
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