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Adolescent male presents with scaly plaque on extremities
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A 17-year-old male presented to pediatric dermatology for scaly pink plaques on the right hand and both feet. The plaques have been present for 2 years. The patient reports that the rash is pruritic, particularly after he exercises. His brother has a similar rash on his feet only. They do not have any pets. Prior treatment of the rash has included over-the-counter terbinafine cream (Lamisil, Novartis Consumer Health) and topical corticosteroids without improvement. The patient is otherwise healthy without a known history of eczema or dry skin. He denies joint pains and a family history of psoriasis. He is right-handed.
On physical exam, the patient is noted to have a scaling pink plaque covering the palmar surface of his right hand. His left hand is completely clear. He has scaling pink plaques on both feet in a moccasin distribution and maceration between his toes. There is no lymphadenopathy, and the patient appears otherwise healthy and comfortable.
What test should you perform next?
A. Complete blood count with differential to screen for mycosis fungoides.
B. IgE level to screen for an immunologic disorder.
C. Patch testing to investigate causes of contact dermatitis.
D. Potassium hydroxide (KOH) preparation or fungal culture to investigate the presence of fungus.
E. Punch biopsy to confirm the diagnosis of psoriasis.
Answer: (D) KOH preparation or fungal culture
Diagnosis: Two feet-one hand syndrome
The differential diagnosis of a scaling rash on the extremities would include psoriasis, irritant or allergic contact dermatitis, and dyshidrotic eczema. For this patient, however, KOH preparation in clinic revealed branching hyphae with septations, consistent with dermatophyte infection. The presentation of unilateral tinea manuum with concurrent bilateral tinea pedis is known as two feet-one hand syndrome. The complete lack of involvement of the patient's non-dominant hand is a clue to this clinical scenario, and KOH preparation offers an easy, noninvasive way to help confirm clinical suspicions.
In an office not equipped or certified to perform KOH preparations, a fungal culture may easily be performed using a readily available bacterial culture swab.
Trichophyton rubrum is the most common cause of tinea pedis and the most common dermatophyte involved in two feet-one hand syndrome. The dermatophyte is spread to the dominant hand by scratching behaviors (ie, contacting the already-infected feet). A case-control study showed that the hand used to scratch is the same hand that develops tinea manuum. It is thought that spread to the opposite, unaffected hand is prevented by the relatively dry environment of the hands compared with the feet.
Treatment of two feet-one hand syndrome involves antifungal therapy (topical or oral) and prevention strategies. Topical antifungals such as ketoconazole, clotrimazole or terbinafine applied twice daily for 2 weeks should clear the infection. Practices that keep the feet dry and clean are important to implement, and wearing open-toed sandals may assist in this regard. Spraying shoes and sneakers with antifungal powders may also help. Treating all affected family members in the home can help prevent spread or reinfection.
Zhan P. Clin Exp Dermatol. 2010;35:468-472.