Bacterial Toe Web Infection

AUTHORS:
Fiona Fang, MD, and Kimberly F. Showalter, MD

A 44-year-old male presents to the emergency department with a 3-week history of rash on his left foot. Despite empiric treatment with over-the-counter antifungal cream, he has experienced worsening pain to the point where he is now unable to ambulate. Patient is otherwise healthy. 

Physical exam reveals superficial desquamation and maceration with surrounding erythema extending from the distal toes to the ball of the left foot. There is purulent malodorous discharge (Figures 1 and 2). 

Figure 1. Plantar surface of foot with interdigital erythema, maceration, desquamation, and discharge consistent with foot intertrigo

Laboratory work-up included a potassium hydroxide (KOH) microscopic preparation of scale from the left foot, obtained using a number 15 blade. Microscopic exam was positive for numerous branching hyphae consistent with dermatophyte infection. Gram stain of the discharge between the toes revealed gram-negative organisms. Final bacterial culture grew Pseudomonas aeruginosa. 

Foot intertrigo, created by friction and moisture trapping between the skin surfaces of toes, is most commonly caused by tinea pedis or yeast.¹ Bacterial infection, however, may mimic or result as a complication of tinea pedis, and should be on the differential for inflammation unresolved after an appropriate course of antifungal medication. Gram-negative toe web infections may present as desquamated, vesiculopustular, and/or macerated eruptions. There is often associated malodorous discharge concentrated in the interdigital web spaces, which occasionally extends to the sole or dorsum of the foot. The differential for maceration of the toe web includes gram-negative infection, gram-positive infection, candida albicans infection, severe tinea pedis, and eczematous dermatitis.²

The most common organism responsible for bacterial toe web infections is Pseudomonas aeruginosa. This may occur as an isolated pathogen, or as part of a polymicrobial infection with other gram-negative bacteria (Escherichia coli, Proteus mirabilis), gram-positive bacteria (Staphylococcus aureus, Staphylococcus saprophyticus, Beta-hemolytic Streptococcus), yeast (Candida albicans) and/or dermatophyte.¹ Initial damage to the stratum corneum by dermatophyte infection often sets the stage for superinfection by gram-negative bacteria. Risk factors associated with infection include hyperhidrosis, cutaneous maceration, closed shoes, and exposure to warm water.¹ Overall, males are more commonly affected than females.^1,2

Treatment of gram-negative foot intertrigo is guided by culture. Most cases are susceptible to third-generation cephalosporins, fluoroquinolones, and aminoglycosides.¹ Topical antibiotic therapy and acetic acid solution soaks may be pursued in patients with mild disease. However, severe cases impairing mobility and extending to the sole of the foot, as in the case of our patient, should be treated with systemic antibiotic therapy. If dermatophytes are also isolated, treatment should include an antifungal agent.¹ 

Figure 2. Dorsum of foot with interdigital erythema, maceration, desquamation, and discharge, consistent with foot intertrigo.

Resistance to antibiotic therapy may occur in gram-negative toe web infections, and incomplete treatment may result in the formation of ulcers with hyperkeratotic rims, which require surgical debridement.³ The prognosis of bacterial intertrigo is favorable overall, particularly when diagnosed early and treated appropriately.²

In this case, our patient was treated for gram-negative toe web infection with a 14-day course of oral ciprofloxacin (500 mg, twice daily), topical terbinafine 1% cream applied twice daily, and 5% acetic acid soaks while using lamb’s wool between toes to prevent accumulation of moisture. Patient failed to present to his follow-up appointment, but subsequent phone call revealed that his rash had resolved completely with treatment. 

References:

1.Aste N, Atzori L, Zucca M, et al. Gram-negative bacterial toe web infection: a survey of 123 cases from the district of Cagliari, Italy. J Am Acad Dermatol. 2001;45:537-541.

2.Lin JY, Shih YL, Ho HC. Foot bacterial intertrigo mimicking interdigital tinea pedis. Chang Gung Med J. 2011;34:44-49.

3.Fangman W, Burton C. Hyperkeratotic rim of gram-negative toe web infections. Arch Dermatol. 2005;141:658.