Tinea Pedis

para>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 1st week of month for 3 months. Not recommended if creatinine clearance <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

11 Ameen M. Epidemiology of superficial fungal infections. Clin Dermatol. 2010;28(2):197 " 201.22 Crawford F, Hollis S Topical treatments for fungal infections of the skin and nails of the foot. Cochrane Database Syst Rev. 2007;(3):CD001434.33 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, Gon §alves 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.

CODES

ICD10

B35.3 Tinea pedis

ICD9

110.4 Dermatophytosis of foot

SNOMED

6020002 Tinea pedis (disorder)
25956006 Tinea pedis due to Trichophyton (disorder)
43581009 Tinea pedis due to Epidermophyton (disorder)

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.

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