Allergic coNtAct DermAtitis of the foot - The Dermatologist

Allergen FocusTable 2. Differential Diagnosis of Allergic Contact Dermatitis of the Foot 18,19Diagnosis Clinical Presentation CommentsACD of the foot (upper/strap) Dorsal foot dermatitis sparing the interdigital spaces. Classic “shoe pattern dermatitis”ACD of the foot (insole) Plantar dermatitis sparing the plantar arch and proximal creases of the toes. Typically spares areas most involved in palmoplantar pustulosis.ACD of the foot (sole)Can present as plantar dermatitis or as localized plaques of dermatitis on thethighs/buttock in patients with a habit of sitting with their legs folded andtheir feet underneath them.ACD of the foot (stiffeners) Dermatitis involving the dorsal toes and heels. Major differential for heel involvement is irritant dermatitis.ACD of the foot (adhesives)Irritant dermatitisMay present with dorsal foot dermatitis, plantar dermatitis or heel and toedermatitis.Parched and glazed appearance of skin with fine scaling that favors the heelsor bridges the dorsal toes and foot in an “apron pattern.”Heel irritant dermatitis is seen more often with frequent wearingof open back shoes such as flip flops. The apron pattern ismore often seen with atopic dermatitis.Atopic Dermatitis Favors the dorsal foot in childhood and the palmoplantar skin in adulthood. Look for other atopic stigmata such as Dennie-Morgan lines,allergic shinners, and hyperlinear thenar eminences.Nummular DermatitisJuvenile Plantar DermatosisPompholyxDyshidrotic EczemaPsoriasisPalmoplantar pustulosisPityriasis rubra pilarisTinea pedisDiscrete, coin-shaped crusted plaques on the dorsal foot.Smooth and glazed appearance with fine scaling localized to the plantar aspectof the forefoot and toes with sparing of the interdigital spaces.Severe sudden outbreaks of intensely pruritic vesicles symmetrically on thepalms, soles and lateral aspects of the digits.Similar to pompholyx but more of a subacute to chronic clinical presentationrather than an acute sudden outbreak.Well-demarcated, erythematous plaques with micaceous scale can be seen onthe dorsal foot. Plantar lesions tend to be more hyperkeratotic and often havea pustular quality. Nail pitting.Bilateral and symmetric erythematous plaques studded with minute pustuleson the central palms and soles.Salmon-orange appearing hyperkeratosis of the plantar foot extending up thesides in the so-called “sandal pattern.” Rarely associated with nail pitting.Dull erythema and fine scale on the sole and sides of the feet in a “moccasinor sandal pattern.” May see similar fine scaling on one palm giving a “onehand, two feet pattern.”Also known as dermatitis plantaris sicca or “sweaty sockdermatitis.”Keratoderma blenorrhagicum is a plantar eruption characteristicof reactive arthritis (Reiter Syndrome).Associated with smoking and thyroid disorders. Likely a localizedacral variant of psoriasis.KOH positive for dermatophyte hyphae is diagnostic.T. mentagrophytes can produce a bullous tinea that favors theplantar arch.trate the textile matrix easily. This createsa reservoir of potential allergens indirect contact with the skin of the footfor prolonged periods of time. Thenormally robust cutaneous barrier ofthe plantar foot may also be diminishedbecause of other conditions like eczemaor dermatophyte infection.Adhesives are necessary in the majorityof footwear for assembly. Theseglues are used to attach the insole tothe sole and to bind various componentsof the shoe top together. They area major source of shoe allergy. As mentioned,the primary relevant shoe adhesivefound on patch testing to causefoot dermatitis is the phenolic resinPTBFR. PTBFR has been shown toaccount for 10% to 20% of allergic reactionsto footwear. 15,16 It has been usedas an additive in rubber glues since the1950s and is ideally suited for footwearmanufacturing due to its strong adhesionto both leather and rubber. 17Heel and toe stiffeners are alsoknown as counters. This component ofthe shoe is meant to retain the overallshape of the shoe while strengtheningthe heel and toe. Stiffeners have aspectrum of complexity, ranging from asimple layer of inert adhesive to a complexweb of polyester or cotton. Similarto insoles, stiffeners can be a source ofexposure to rubber compounds, adhesivesand biocides. 16Differential DiagnosisThe differential diagnosis for an eczematouseruption of the foot can beclinically challenging. A categorical approachis helpful. The majority of casescan be sorted into one of the followingprinciple categories: (1) exogenousdermatitis, (2) endogenous dermatitis,(3) acral papulosquamous entities, (4)infectious entities and (5) hybrid dermatitis.18,19 Table 2 highlights this differentialdiagnosis.Exogenous dermatitis includes bothirritant and allergic contact dermatitis.The morphology of this group is theprototypical spectrum of acute, subacuteand chronic eczematous eruptions. Itis typical to see a poorly demarcated,spreading, erythematous and edematous,papulovesicular eruption. However, asthe lesions progress along the spectrumto a more chronic state, there is morescaling and lichenification, which cancause some confusion clinically withthe papulosquamous eruptions. Symptomatologyis useful in that pruritusfavors an allergic etiology and burningand stinging are more often seen withirritant etiologies. Finally, regional distributionis important to note. The clas-22 November 2012 | The Dermatologist ® | www.the-dermatologist.com