Allergic coNtAct DermAtitis of the foot - The Dermatologist

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Allergen FocusIn this column, we highlight ACDand explore top relevant allergens, regional-and topic-based dermatitis presentationsand clinical tips and pearls fordiagnosis and treatment.Allergic Contact Dermatitis of the FootFoot dermatitis can be a chronic andrecalcitrant condition. Disability frompainful fissures and impaired gait maybe seen. Active dermatitis may lead to aweakened cutaneous barrier, which increasesthe potential risk for infection.Occupational implications also exist, inthat many patients require protectivefootwear for employment. If an allergyto this protective barrier equipment develops,the patient may be forced to seekother employment.When discussing ACD of the foot,there is a relatively stable microenvironmentof contactants, composed principallyof rubber compounds and accelerators,chromates, adhesives, dyes andretained contaminants, such as topicalmedicaments. 9-13 Table 1 highlightsthe most common of these allergens.In cultures that tend to favor the useof footwear, the shoe and sock encapsulatethis microenvironment and arethe source of potential allergens. Studieshave estimated that the prevalence offoot dermatitis due to shoes ranges from3.3% to 11.7% of patch-test patients. 14The development of ACD of the foot isfavored by friction and the hot, humidenvironment within the shoe. 15While this may initially appearstraightforward, one realizes on closerinspection that the anatomy of footwearis quite complex. The approach tofootwear can be simplified by consideringfive separate systems: (1) uppers orstraps, (2) soles, (3) insoles, (4) adhesivesand (5) heel and toe stiffeners. 16The upper or strap is the componentof the footwear that attaches to the soleand covers the dorsal foot. Leather isTable 1. Top Allergens 14,18AllergenMercaptobenzothiazoleMercapto MixThiuram MixCarba MixMixed Dialkyl ThioureasDithiodimorpholineBlack Rubber MixPotassium DichromateGlutaraldehydeFormaldehydep-tert-butylphenol formaldehyde resin (PTBFR)ColophonyEthyl/Methyl AcrylateDiaminodiphenylmethanecommonly utilized and may thereforebe a source of chromate exposure, dependingon how the leather was tanned.Some types of leather undergo a multisteptanning process. This process maystart with chromate tanning and involvesubsequent tanning with formaldehydeor glutaraldehyde. 12,16 In a retrospectiveanalysis published in 2007 by the NorthAmerican Contact Dermatitis Group(NACDG), potassium dichromate wasfound to be the second-most frequentshoe-related allergen. Only the adhesivep-tert-butylphenol-formaldehyde resinFoot dermatitis can be a chronic and recalcitrant condition.Disability from painful fissures and impaired gait may be seen.Active dermatitis may also lead to a weakened cutaneousbarrier, which increases the potential risk for infection.Occupational implications also exist, in that many patientsrequire protective footwear for their employment.NickelPreservatives(PTBFR) was more frequently positiveon patch testing. 14The sole of a shoe is the base. Thechemical composition of the sole dependson the type of shoe; leather, neoprene,polyurethane and various types ofrubber are commonly used. Neopreneis oil-resistant and commonly foundin the sole of occupational footwear. 16LocationRubberRubberRubberRubberRubberRubberRubberLeatherLeatherLeatherAdhesivesAdhesivesAdhesivesPolyurethaneLace eyelets, bucklesBiocidesWhile overall the single most commonshoe allergen in North America appearsto be PTBFR followed by chromate,taken as a group, rubber additives causea greater number of reactions. 14 In otherwords, rubber-related chemicals are themost common shoe allergen categoryoverall. This group includes carba mix,thiuram mix, mercaptobenzothiazole(MBT), mercapto mix, mixed dialkylthioureas, dithiodimorpholine (DTDM)and black rubber mix.The insole provides cushion and archsupport. The composition of the insolemay be leather, polyurethane, neopreneor a composite of rubber or paper fibers.Composite fiber insoles are cheaperand may be found in less expensivefootwear. These fibers are typically heldtogether by a resinous glue. To preventmicrobial degradation of these fibers, abiocides (preservative) is also typicallyadded. 16 Insoles of a shoe come in directcontact with the sock and plantarfoot region. While the plantar foot is innatelyresistant to ACD (because to therelatively thick skin of this region), thereare several key factors that can lead tosensitization. Potential sensitizing haptensof the insole may be released withheat, friction and sweat over time. Becausemost socks are porous, potentialallergens leached from the insole infil-November 2012 | The Dermatologist ® | www.the-dermatologist.com 21
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
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Allergic coNtAct DermAtitis of the foot - The Dermatologist

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