ATHLETE’S FOOT/TINEA PEDIS

Definition:
Skin infection of feet caused by dermatophytes. Patient may complain of itchy feet/toes or rash on feet and toes. Often it is a incidental finding on examination of patient with exposed feet. There are two types, bullous tinea that can affect entire sole of foot and interdigital tinea which occurs betweens the toes.   Typically occurs 20-50 but any age can be affected and more prominent in men.

Risk Factors – warm humid weather, hyperhidrosis, occlusive footwear, immunosuppression, DM

Mechanism of Infection:   It is the most common dermatophyte infection, and is contagious. (1)

DDx:   Impetigo, candida, allergic contact dermatitis, dyshidrotic eczema, psoriasis.

Exam: Inspection of feet will reveal erythema along with scaling at the border of the infection. Common areas are between toes or the plantar aspect of the foot.   This is called a “moccasin” appearance as it typically covers the entire plantar aspect. There may be associated hyperhidrosis.  May see vesicles or bullae and in chronic cases fissures between the digits.

Investigations: None typically needed but may be especially useful to differentiate from dyshidrotic eczema. A KOH test can be performed by scraping the scaly “active border” with a scalpe blade and dropped into a 10 to 20% KOH solution. (2) This can be sent to lab for microscopic observation for fungal hyphae.

Management:

Non-medicinal:
Frequent changing of socks,
Application of drying powder (talcum or bond)
Topical antiperspirants
Drying feet without rubbing, using hairdryer (3)
Soaks – Aluminum acetate solution
Antifungal Creams– Terbinafine (Lamisil), clotrimazole 1%, ketoconazole 2% topically BID for 2-6 weeks.  Interdigital infection may only require 1 week to treat. (4)

For severe disease (bullous type):
Keralyt gel (6% salicylic acid) nightly under occlusion (3)
Or
Urea 20-40% lotion (Carmol 20 or Carmol 40)
Systemic treatment may be required in which case monitoring of liver enzymes is recommended.
Terbinafine 250mg po daily X 2 weeks
Itraconazole 100-200mg for 2-4 weeks (1,2)

References: 
(1) Domino FJ. The 5-minute clinical consult, 2014. 22nd ed. ed.

(2) VisualDx. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2011.

(3) Primary care medicine : office evaluation and management of the adult patient. 6th ed. ed. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2009.

(4) www.uptodate.com

Dr. Neil Dilworth (2014/7/17  PR KA)