Woman With Pruritic, Discolored Toes

The Case: A 48-year-old woman’s toes and feet have been pruritic for several weeks. She sought treatment in an emergency department 10 days earlier, where terbinafine 1% cream was prescribed for a suspected fungal infection. The pruritus has not diminished. For the past several days, the patient has noticed blackish areas between her toes. She denies fever, chills, eczema, asthma, psoriasis, and diabetes. She has not changed her soap or laundry detergent, has not been in contact with sick persons, has not traveled, and does not use hot tubs. She always wears tennis shoes. Examination of the feet reveals black and bluish green focal discolorations beneath the right great toenail, as well as bluish green discolorations in the toe web spaces between the second and fifth toes bilaterally. There is no discharge or odor. Which of these conditions best explains the findings? •Tinea pedis •Erythrasma •Toe web infection •Contact dermatitis Answer on next page , Discussion:  This patient has a toe web infection. Also known as interweb foot impetigo, this relatively common infection is often seen in persons who wear tight-fitting or closed-toe footwear, as well as persons who participate in strenuous recreational, athletic, or work-related activities. In this patient, a Wood lamp examination revealed fluorescence and cultures were positive for Pseudomonas aeruginosa. Besides P aeruginosa, organisms frequently responsible for toe web infections include Proteus, Acinetobacter, Moraxella, and Erwinia species. Patients often complain of burning and discomfort as well as difficulty in walking. Physical examination typically reveals purulent and often malodorous exudates, edema and erythema of the toes, macerations, hyperhidrosis, and vesiculopustules. In addition, discoloration is often associated with Pseudomonas infection. Predisposing factors include tinea pedis, trauma, and immunocompromised status. Toe web infections affect patients of all ages and are 4 times more common in men than in women. The workup of patients with suspected toe web infection includes fungal and bacterial cultures and a potassium hydroxide evaluation. A Wood lamp examination that demonstrates greenish white fluorescence helps confirm the diagnosis of Pseudomonas infection. Treatment begins with personal hygiene measures, including drying the interdigital spaces and wearing open sandals or open-weave shoes. The use of an antimicrobial soap, such as chlorhexidine, helps reduce the number of Gram-negative organisms. Antibiotic options include topical econazole or carbol-fuchsin paint and oral ciprofloxacin. Indications for hospitalization and aggressive management are deep space infections (which may require surgical debridement) and signs of septicemia.  Initially endemic in parts of Africa, Australia, and Southeast Asia, tinea pedis is one of the world’s most common dermatophyte infections; the usual culprit agent is Trichophyton rubrum. The typical presentation is interdigital, especially between the fourth and fifth toes. Pruritus, maceration, fissuring, erythema, and scaling are the usual findings. Less common presentations include vesicular or bullous lesions (sometimes complicated by lymphangitis, cellulitis, or adenopathy), ulcerative lesions (more commonly seen in immunocompromised and diabetic patients), and chronic hyperkeratotic lesions (characterized by scaling and plantar erythema). Tinea pedis is more common during the warmer months and in tropical climates; the infection progresses slowly. Occlusive footwear and communal bathing or swimming increase the risk of infection. Secondary bacterial infection may occur; the culprit organisms include Pseudomonas, Candida albicans, Staphylococcus aureus, and Proteus. Tinea pedis usually responds to a topical or oral antifungal agent; sometimes topical and oral therapy is prescribed. Nail involvement requires an oral agent, such as itraconazole, terbinafine, or fluconazole. Erythrasma, a chronic superficial bacterial infection caused by Corynebacterium minutissimum, is seen more frequently in tropical and subtropical regions than in temperate ones. Although the condition is usually benign, invasive infection may develop in immunocompromised patients. Predisposing factors include diabetes, obesity, and hyperhidrosis. Erythrasma is often asymptomatic. The skin folds become dark and discolored; involvement of the trunk and limbs may also occur. Erythrasma preferentially affects the male genital crural area, with reddish brown macular patches. Infection in the toe webs produces fissuring, scaling, and maceration; under the Wood lamp, the area fluoresces coral-red. Treatment consists of erythromycin, 1 g/d for 5 to 7 days, plus miconazole 2% cream or clindamycin hydrochloride 2% aqueous solution. Contact dermatitis affects all age groups. The 4 types of contact dermatitis—based on the mechanism of response—are allergic, irritant, and contact dermatitis and photodermatitis. The inflammatory response is categorized as acute, subacute, or chronic, or as contact urticaria: • The acute group is characterized by clear fluid-filled bullae or vesicles on erythematous skin; the lesions may become exudative. • Subacute conditions feature papule formation with less edema. • Chronic contact dermatitis presents with fissuring, scaling, and occasionally lichenification. • A wheal-and-flare reaction at the contact site is characteristic of contact urticaria. Treatment includes removal of the offending agent and the use of emollients; antipruritic measures; and topical soaks with cool tap water, Burow solution, or silver nitrate solution. FOR MORE INFORMATION: Aly R, Maibach HI. Effect of antimicrobial soap containing chlorhexidine on the microbial flora of skin. Appl Environ Microbiol. 1976;31:931-935. Amonette RA, Rosenberg EW. Infection of toe webs by gram-negative bacteria.  Arch Dermatol. 1973;107:71-73. Eaglstein NF, Marley WM, Marley NF, et al. Gram-negative bacterial toe web infection: successful treatment with a new third generation cephalosporin. J Am Acad Dermatol. 1983;8:225-228. Hall JH, Callaway JL, Tindall JP, Smith JG Jr. Pseudomonas aeruginosa in dermatology. Arch Dermatol. 1968;97:312-324. Leyden JJ, Kligman AM. Interdigital athlete’s foot. The interaction of dermatophytes and resident bacteria. Arch Dermatol. 1978;114:1466-1472. Mandell GL, Bennett JE, Dolin R. Mandell, Douglas and Bennett’s Principles and Practice of Infectious Disease. 6th ed. Philadelphia: Churchill Livingstone; 2005. Taplin D, Zaias N, Rebell G. Environmental influences on the microbiology of the skin. Arch Environ Health. 1965;11:546-550.