BASICSElisabeth L. Backer, MD
BASICS
DESCRIPTION
• Superficial infection of the feet caused by dermatophytes
• Most common dermatophyte infection encountered in clinical practice
• Often accompanied by tinea manuum, tinea unguium, and tinea cruris
• Two clinical forms: acute and chronic; both are contagious
• System(s) affected: skin/exocrine
• Synonym(s): athlete’s foot
EPIDEMIOLOGY
• Predominant age: 20 to 50 years, although can occur at any age (1)[C]
• Predominant gender: male > female
Prevalence
4% of population
Pediatric Considerations
Rare in younger children; common in teens
Geriatric Considerations
Elderly are more susceptible to outbreaks because of immunocompromise and impaired perfusion of distal extremities.
ETIOLOGY AND PATHOPHYSIOLOGY
Superficial infection caused by dermatophytes that thrive only in nonviable keratinized tissue.
• Trichophyton mentagrophytes (acute)
• Trichophyton rubrum (chronic)
• Trichophyton tonsurans
• Epidermophyton floccosum
Genetics
No known genetic pattern
RISK FACTORS
• Hot, humid weather
• Sweating
• Occlusive/tight-fitting footwear
• Immunosuppression
• Prolonged application of topical steroids
GENERAL PREVENTION
• Good personal hygiene
• Wearing rubber or wooden sandals in community showers, bathing places, locker rooms
• Careful drying between toes after showering or bathing; blow-drying feet with hair dryer may be more effective than drying with towel.
• Changing socks and shoes frequently
• Applying drying or dusting powder
• Applying topical antiperspirants
• Putting on socks before underwear to prevent infection from spreading to groin
COMMONLY ASSOCIATED CONDITIONS
• Hyperhidrosis
• Onychomycosis
• Tinea manuum/unguium/cruris/corporis
DIAGNOSIS
HISTORY
• Itchy, scaly rash on foot, usually between toes; may progress to fissuring/maceration in toe web spaces.
• May be associated with onychomycosis and other tinea infections
PHYSICAL EXAM
• Acute form: self-limited, intermittent, recurrent; scaling, thickening, and fissuring of sole and heel; scaling or fissuring of toe webs; or pruritic vesicular/bullous lesions between toes or on soles
• Chronic form: most common; slowly progressive, pruritic erythematous erosion/scales between toes, in digital interspaces; extension onto soles, sides/dorsum of feet (moccasin distribution); if untreated, may persist indefinitely
• Other features: strong odor, hyperkeratosis, maceration, ulceration
• Tinea pedis may occur unilateral or bilateral.
• Seconday eruptions called dermatophytid reactions may occur at distant sites.
DIFFERENTIAL DIAGNOSIS
• Interdigital type: erythrasma, impetigo, pitted keratolysis, candidal intertrigo
• Moccasin type: psoriasis vulgaris, eczematous dermatitis, pitted keratolysis
• Inflammatory/bullous type: impetigo, allergic contact dermatitis, dyshidrotic eczema (negative KOH examination of scrapings), bullous disease
DIAGNOSTIC TESTS & INTERPRETATION
Wood lamp exam will not fluoresce unless complicated by another fungus, which is uncommon: Malassezia furfur (yellow to white), Corynebacterium (red), or Microsporum (blue-green).
Initial Tests (lab, imaging)
Testing is not needed in typical presentation.
• Direct microscopic exam (potassium hydroxide) of scrapings of the lesions
• Culture (Sabouraud medium)
Test Interpretation
• Potassium hydroxide preparation: septate and branched mycelia
• Culture: dermatophyte
TREATMENT
Treatment is generally with topical antifungal medications for up to 4 weeks and is more effective than placebo:
• Acute treatment
– Aluminum acetate soak (Burow solution; Domeboro, one pack to one quart warm water) to decrease itching and acute eczematous reaction
– Antifungal cream of choice BID after soaks
• Chronic treatment:
– Antifungal creams BID, continuing for 3 days after the rash is resolved: terbinafine 1% (possibly most effective topical), clotrimazole 1%, econazole 1%, ketoconazole 2%, tolnaftate 1%, etc. (2)[A]
– May try systemic antifungal therapy; see below (consider if concomitant onychomycosis or after failed topical treatment)
GENERAL MEASURES
• Soak with aluminum chloride 30% or aluminum subacetate for 20 minutes BID.
• Careful removal of dead/thickened skin after soaking or bathing
• Treatment of shoes with antifungal powders
• Avoidance of occlusive footwear
• Chronic or extensive disease or nail involvement requires oral antifungal medication and systemic therapy.
MEDICATION
For use when topical therapy has failed
First Line
• Systemic antifungals (3)[A]:
– Itraconazole (Sporanox): 200 mg PO BID for 7 days (cure rate >90%)
– Terbinafine (Lamisil): 250 mg/day PO for 14 days
• If concomitant onychomycosis:
– Itraconazole: 200 mg PO BID for first week of month for 3 months. Liver function testing is recommended.
– Terbinafine: 250 mg/day PO for 12 weeks, or pulse dosing: 500 mg/day PO for first week of month for 3 months. Not recommended if creatinine clearance is <50 mL/min.
• Pediatric dosing options:
– Griseofulvin: 10 to 15 mg/kg/day or divided
– Terbinafine:
10 to 20 kg: 62.5 mg/day
20 to 40 kg: 125 mg/day
>40 kg: 250 mg/day
• Itraconazole: 5 mg/kg/day
• Fluconazole: 6 mg/kg/week
• Contraindications: itraconazole, pregnancy Category C
• Precautions: All systemic antifungal drugs may have potential hepatotoxicity.
• Significant possible interactions: Itraconazole requires gastric acid for absorption; effectiveness is reduced with antacids, H2 blockers, proton pump inhibitors, etc. Take with acidic beverage such as soda if on antacids.
Second Line
• Systemic antifungals: griseofulvin 250 to 500 mg of microsize BID daily for 21 days
• Contraindications (griseofulvin):
– Patients with porphyria, hepatocellular failure
– Patients with history of hypersensitivity to griseofulvin
• Precautions (griseofulvin):
– Should be used only in severe cases
– Periodic monitoring of organ-system functioning, including renal, hepatic, and hematopoietic
– Possible photosensitivity reactions
– Lupus erythematosus, lupus-like syndromes, or exacerbation of existing lupus erythematosus has been reported.
• Significant possible interactions (griseofulvin):
– Decreases activity of warfarin-type anticoagulants
– Barbiturates usually depress griseofulvin activity.
– May potentiate effect of alcohol, producing tachycardia and flush
ISSUES FOR REFERRAL
If extensive or resistant disease, especially in immunocompromised host
ADDITIONAL THERAPIES
• Treatment of secondary bacterial infections
• Treatment of eczematoid changes
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Avoid sweating feet.
Patient Monitoring
Evaluate for response, recognizing that infections may be chronic/recurrent.
DIET
No restrictions
PATIENT EDUCATION
See “General Prevention.”
PROGNOSIS
• Control but not complete cure
• Infections tend to be chronic with exacerbations (e.g., in hot weather).
• Personal hygiene and preventive measures such as open-toed sandals, careful drying, and frequent sock changes are essential.
COMPLICATIONS
• Secondary bacterial infections (common portal of entry for streptococcal infections, producing lymphangitis/cellulitis of lower extremity)
• Eczematoid changes
REFERENCES
1. Ameen M. Epidemiology of superficial fungal infections. Clin Dermatol. 2010;28(2):197–201.
2. Crawford F, Hollis S. Topical treatments for fungal infections of the skin and nails of the foot. Cochrane Database Syst Rev. 2007;(3):CD001434.
3. Bell-Syer SE, Khan SM, Torgerson DJ. Oral treatments for fungal infections of the skin of the foot. Cochrane Database Syst Rev. 2012;(10):CD003584.
ADDITIONAL READING
• Gupta AK, Cooper EA. Update in antifungal therapy of dermatophytosis. Mycopathologia. 2008;166(5–6):353–367.
• Rotta I, Sanchez A, Gonçalves PR, et al. Efficacy and safety of topical antifungals in the treatment of dermatomycosis: a systematic review. Br J Dermatol. 2012;166(5):927–933.
SEE ALSO
Dermatitis, Contact; Dyshidrosis
CODES
ICD10
B35.3 Tinea pedis
CLINICAL PEARLS
• Treatment is generally with topical antifungal medications for up to 4 weeks.
• Tinea pedis is often recurrent/chronic in nature.
• Careful drying between toes after showering or bathing helps prevent recurrences. (Blow drying feet with hair dryer may be more effective than drying with towel.)
• Socks should be changed frequently. Put on socks before underwear to prevent infection from spreading to groin (tinea cruris).
• Dusting and drying powders (containing antifungal agents) may prevent recurrences.