Squaric acid immunotherapy for warts in children

Squaric acid immunotherapy for warts in children Nanette B. Silverberg, MD, Joseph K. Lim, BS, Amy S. Paller, MD, and Anthony J. Mancini, MD Chicago, Illinois Background: Warts are a common pediatric skin infection caused by human papillomavirus (HPV). Spontaneous clearance of warts involves anti-HPV immunity, which may be enhanced by contact sensitizers. Squaric acid dibutylester (SADBE) is a nonmutagenic sensitizing agent useful for immunotherapy of alopecia areata. Objective: We hypothesized that SADBE home application might be effective therapy for warts. Methods: An open-label, retrospective study of 61 children with warts was performed. Sensitization with 2% SADBE on the forearm was followed with home application of 0.2% SADBE to warts 3 to 7 nights per week for at least 3 months. Results: Complete clearing occurred in 34 patients (58%), with a mean duration of therapy of 7 weeks. Partial clearing occurred in 11 (18%), and no response in 14 (24%). Clearance correlated with plantar distribution, wart duration under 2 years (P<.05), and first-line therapy with SADBE. Mild side effects occurred in one third of patients, were limited most commonly to mild erythema at the site of sensitization, and necessitated discontinuation of therapy in only 2 patients. Conclusion: SADBE topical immunotherapy is a safe, effective option for home therapy of warts in children. (J Am Acad Dermatol 2000;42:803-8.)

W

arts remain an exceedingly common dermatologic problem in the pediatric population. They are believed to occur in up to 10% of all children, with a peak age of 12 to 16 years.1,2 Infection with the etiologic agent human papillomavirus (HPV) occurs via a break in the skin, allowing infection of the basal layer of keratinocytes.1 Unlike most cutaneous infections, infection of the skin with HPV often does not incite an inflammatory response, and therefore the lesions usually do not clear quickly. Studies of the natural course of warts indicate that two thirds clear spontaneously by 2 years of infection.3,4 Clearance requires the induction of HPV-specific cytotoxic T cells.4,5 Other components of the immune system have also been implicated in wart immunity, including the generation of

From the Departments of Pediatrics and Dermatology, Northwestern University Medical School, Children’s Memorial Hospital. Reprint requests: Anthony J. Mancini, MD, Division of Dermatology, Children’s Memorial Hospital, 2300 Children’s Plaza, #107, Chicago, IL 60614. Copyright © 2000 by the American Academy of Dermatology, Inc. 0190-9622/2000/$12.00 + 0 16/1/103631 doi:10.1067/mjd.2000.103631

HPV-specific antibodies,6,7 which have been shown to confer better host immunity, macrophage activation, and increased expression of cytokines, especially interferon gamma.8-11 Despite our knowledge about the function of the immune system in wart clearance, treatments for warts have traditionally been destructive mechanisms to eradicate infection from the epidermis.1,12 These have included chemovesicants, such as salicylic acid and trichloroacetic acid, as well as more painful methods, such as liquid nitrogen cryotherapy and electrodesiccation.1,12,13 Other methods such as intralesional bleomycin have used sclerosing and cytotoxic effects.14 Intralesional agents that induce immunity, such as interferon, can be exceedingly painful to administer and can have systemic side effects, precluding their practical usage in children.8-11 Oral immune stimulant therapy with levamisole was originally described in 1979.15 More recently, cimetidine, a histamine (H2) blocker that increases cell-mediated immunity via suppression of CD8 cell activity, has been proposed as a preferable immunostimulant.16,17 Although cimetidine is often efficacious, some pediatric patients do not respond, and others may not tolerate the medication. In addition, the administra803

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tion of cimetidine 2 to 3 times daily for 2 to 3 months limits patient compliance. Topical immunotherapy was initially described with dinitrochlorobenzene (DNCB),18-21 which is a potent topical sensitizing agent that was also found to be mutagenic by the Ames test. Many reports have lauded the efficacy of this immunotherapeutic agent for treating both warts19-22 and alopecia areata,23-26 but the mutagenic potential has limited its clinical usefulness. Two other topical sensitizing agents have been suggested for wart immunotherapy: diphencyclopropenone (DCP)27-31 and squaric acid,32,33 which is available both as squaric acid dibutylester (SADBE) and squaric acid ethylester. Although efficacious in wart immunotherapy as well as in alopecia areata, local side effects with DCP have been reported to be more frequent and often severe,30 and the product is photoinactivated with minimal light exposure.34 There has also been a report of 3 patients with erythema multiforme–like eruptions associated with DCP.35 SADBE, which forms a stable solution in acetone,36 is a highly potent topical sensitizer used in crystal refraction studies and for the formation of industrial dyes. Two studies have evaluated weekly or biweekly in-office application of SADBE to warts,32 and several studies have demonstrated the longterm safety of SADBE usage in children.37-41 Because of the unrealistic expectation that children will come in weekly or biweekly for treatment of warts, this study evaluated at-home application of SADBE in children with warts.

METHODS Between June 1997 and June 1998, 61 patients with nonfacial common warts were treated with SADBE immunotherapy in the dermatology clinic of the Children’s Memorial Hospital, Chicago, Illinois. SADBE was obtained from the Spectrum Chemicals Co. (Gardena, Calif) and was mixed to the desired concentration in acetone by the pharmacy staff. This article summarizes the results seen in these patients, which we retrospectively decided to publish after noting the impressive response to therapy. The risks and potential benefits of squaric acid immunotherapy were explained to patients and parents both verbally and with the use of educational handout materials, and verbal consent was obtained. Patients were sensitized on the upper arm with 2% SADBE in acetone by open application with a cotton-tipped applicator and were instructed not to rinse the area for at least 12 hours. After 7 to 10 days, and regardless of whether a sensitization reaction occurred, patients or parents were instructed in the office regarding the proper method of application of SADBE to warts and

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were instructed to treat all nonfacial lesions. Application of SADBE was performed while wearing protective gloves. Parents were instructed to apply 0.2% SADBE 3 times weekly, increasing the frequency of application by one application per week until nightly application was achieved, as tolerated. Follow-up examination was performed by a physician at 6 weeks, and the SADBE concentration was increased by 0.1% to 0.3% for nonresponders. Further follow-up examinations were performed at 4- to 6-week intervals and by telephone interviews when necessary. Physician assessment at completion of therapy was performed in all nonresponders and partial responders. Of patients with clearance, follow-up was achieved by phone interview of 29 patients and by physician examination of 5. Study completion was defined as completion of at least 3 months of therapy or use of SADBE until warts cleared (if occurring before 3 months). For patients treated with cimetidine (either before or concomitant with SADBE therapy), the dose was 40 mg/kg daily divided 2 or 3 times daily, based on previous reports.16 History of atopy was significant for 4 patients with atopic dermatitis, 3 with keratosis pilaris (one with concurrent atopic dermatitis), and 4 with asthma. Two patients had a history of HIV infection. No patients had histories of organ transplantation or systemic immunosuppression.

RESULTS The results are summarized in Table I. Of 61 patients receiving SADBE treatment, 59 completed a 3-month trial of therapy, with the exception of those patients who cleared before 3 months had been reached. Two patients discontinued therapy before 3 months, 1 because of burning upon application and the other because of a florid sensitization reaction. Of the 59 patients who completed the study, 34 (59%) experienced complete clearing of their warts, with an average initial response time of 3 weeks (range, 3 days to 3 months) and mean clearance time of 7 weeks (range, 4 days to 4 months). Fig 1 demonstrates complete clearing in a representative patient. Another 11 (19%) had partial improvement with first response noted on average at 3 months (range, 2 weeks to 5 months) and continuation of treatment for 5.6 months (range, 3 months to 1 year). Fourteen patients (24%) did not respond or experienced progression while receiving therapy for an average of 3.85 months (range, 3 to 7 months). Patients ranged in age from 3 to 17 years, with a mean age of 9.5 years. A total of 50 patients (85%) were 5 to 14 years of age. Five patients were younger than 5 years, and 4 patients were older than 14 years. Mean duration of wart infection was 14, 27, and 44 months for the

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Table I. Results of SADBE treatment No. of patients (%)

Total patients 59 Sex (male/female) Average age (y) Average duration of warts (mo) Average No. of warts Location of warts Feet (n = 22) Plantar only (n = 10) Legs (n = 16) Hands (n = 44) Arms (n = 4) Body (n = 1) Face (n = 14) Previous therapies Cryotherapy + salicylic acid (n = 12) Cryotherapy only (n = 11) Cryotherapy + cimetidine + salicylic acid (n = 9) Cryotherapy + cimetidine (n = 7) Salicylic acid only (n = 6) None (n = 6) Cimetidine + salicylic acid (n = 3) Cimetidine only (n = 1) Cryotherapy + tretinoin (n = 1) Cimetidine + tretinoin (n = 1) Cimetidine + salicylic acid + carbon dioxide laser (n = 1) Cryotherapy + salicylic acid + pulsed dye laser (n = 1) Positive sensitization reaction Maximum frequency of use Daily 3-6 times per week 1-2 times per week† Maximum percent SADBE used 0.2% >0.2% Average time to initial response (wk) Average length of therapy (wk) Concomitant therapies None (n = 47) Cimetidine only (n = 7) Pulsed dye laser only (n = 2) Liquid nitrogen only (n = 3) Cimetidine and pulsed dye (n = 1) Side effects Erythema (n = 15) Pruritus (n = 4) Burning (n = 2)

Cleared

Improved

No response

34 (58) 21/13 9 14 12

11 (18) 6/5 9.8 27 19

14 (24) 7/7 8.7 44 14

16 (47) 9 (26) 10 (29) 22 (65) 1 (3) 0 (0) 7 (20)

3 (27) 0 (0) 2 (18) 10 (91) 1 (9) 1 (9) 2 (18)

3 (21) 1 (7) 4 (28) 12 (86) 2 (14) 0 (0) 5 (36)

7 (20) 8 (24) 4 (12) 1 (3) 4 (12) 6 (18) 2 (6) 1 (3) 1 (3) 0 (0) 0 (0) 0 (0) 9 (26)

1 (9) 2 (18) 4 (36) 3 (21) 1 (9) 0 (0) 0 (0) 0 (0) 0 (0) 1 (9) 1 (9) 1 (9) 3 (27)

4 (28) 1 (7) 1 (7) 3 (21) 1 (7) 0 (0) 1 (7) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 1 (7)

20 (59) 12 (35) 2 (6)

5 (45) 6 (55) 0 (0)

11 (78) 3 (21) 0 (0)

31 (91) 3 (9) 3 7

6 (55) 5 (45) 12 22

8 (57) 6 (43) NA 15

29 (85) 4 (12) 0 (0) 1 (3) 0 (0)

7 (64) 2 (18) 2 (18) 0 (0) 0 (0)

11 (78) 1 (7) 0 (0) 2 (14) 1 (7)

8 (24) 3 (9) 0 (0)

5 (45) 1 (9) 2 (18)

2 (14) 0 (0) 0 (0)

*Percentages in parentheses refer to the percentage of patients in that response category. †Patients whose application frequency was reduced because of side effects.

cleared, improved, and nonresponder groups, respectively, with an overall mean of 24 months. Duration of wart infection was significantly less (P<.05) in the group whose warts cleared than in

the group of nonresponders. Nearly all patients (89%) had attempted other forms of treatment before topical immunotherapy. Of the 2 patients with HIV, 1 cleared and 1 improved. Of the 4 patients

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A

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B Fig 1. A, Patient before squaric acid immunotherapy. B, After 8 weeks of nightly application of 0.2% squaric acid.

with atopic dermatitis, 1 cleared and 3 were nonresponders, although they all tolerated nightly therapy without discomfort. Frequency of use of SADBE did not affect clearance because nonresponders were far more likely to achieve daily application than the cleared or improved patients. Patients were followed up for 1 month to 2 years (average, 4 months), and to date no recurrences have been reported or observed. A trend was observed in that SADBE sensitization reactions were more likely to occur in responders (P<.05). Sensitization reactions appeared as erythematous patches or plaques on the upper arm in the distribution of the SADBE 2% application site. One patient experienced erythematous plaque formation on the entire arm. A total of 22 patients (37%) experienced side effects, which consisted of mild erythema, burning, and pruritus. These side effects were limiting in only 4 patients, 2 of whom discontinued usage and 2 of whom subsequently reduced the frequency of application to less than 3 times weekly. After initiation of home therapy, patients occasionally reported exacerbation of erythema at the sensitization site. One patient had generalized urticaria and one complained of mild abdominal pain that was not temporally related to the times of application.

DISCUSSION This study suggests that SADBE appears to be a safe and effective home-applied therapy for warts in children. Our cure rate of 58% is comparable to weekly office application reported by Iijima and Otsuka32 (60%). SADBE, as used by our patients, represents a convenient, painless treatment with few side effects. Such therapy is desirable for pediatric patients, whereas painful, destructive procedures

are difficult to perform and are associated with undue emotional trauma for the child. These results are comparable to previous studies of DNCB and DCP, which have demonstrated clearance rates of 60% to 91%. DNCB has been shown to be mutagenic and is therefore not ideal for pediatric patients. DCP is not mutagenic, but is rapidly photoinactivated34 and may cause more severe local side effects in many patients, with side effects occurring in up to 49% of patients.30 SADBE home therapy is effective both as a first- and second-line agent in the treatment of childhood warts. Clearing in this study took place as early as 4 days, and on average in 7 weeks rather than the minimum of 3 months required for other previously reported forms of immunotherapy, including weekly SADBE. Erythema at sites of home application, which likely reflects locally increased immunity, was rare and, when it occurred, mild and usually not limiting. Patients who experienced clearing of warts responded and reached a clear state rapidly. All but one of these responders had warts that cleared within 3 months of starting therapy, with the warts of the final patient clearing at 4 months. None of our patients have had wart recurrence, with a mean follow-up of 4 months. Eight patients have remained clear for more than 6 months, 4 for more than 8 months, and 2 for 1 year. We believe this long-term remission is related to the onset of anti-HPV immunity, a clear advantage when compared with the high recurrence rates seen after destructive wart therapies. In the present study, foot warts responded better to SADBE therapy, and 9 of 10 patients with isolated plantar warts experienced complete clearing. Shorter duration of wart infection before SADBE usage also correlated with better chance of clearing,

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with longer durations being associated with a higher failure rate. Surprisingly, the efficacy of immunotherapy did not improve with concurrent cimetidine usage, a benefit noted with concurrent DNCB and cimetidine therapy.42,43 This may be because of the rapidity of response in our patients. Randomized studies comparing combined cimetidine and SADBE therapy with SADBE alone are required to further assess the efficacy of combined therapy. The mechanism of action of SADBE likely involves the generation of a delayed-type hypersensitivity reaction at the site of the wart, requiring antigen presentation to CD4 cells and the induction of cytotoxic lymphocyte killing of virally infected cells.5,6,30,44 Immunotherapies may work by acting as a hapten, complexing with viral antigens and thereby inducing a papillomavirus-specific antigen presentation and immune response.4-7 Other theories on the mechanisms of immunotherapy suggest there are nonspecific antiviral effects associated with the local cytokine milieu produced by these powerful allergens. Because patients have been reported to experience clearing at distal sites (including untreated lesions in many of our patients), systemic cytokine alterations are likely to be contributory to the immune response generated.20 Finally, antibodydependent cell-mediated cytotoxicity has been demonstrated to be a possible mechanism in wart clearance.4,7 SADBE efficacy is likely to reflect a combination of all of these immune mechanisms and therefore may translate into long-term immune protection from HPV infection. There exist some limitations of our study. This was a retrospective collection of data, and no attempt was made to randomize, control, or blind this study. Furthermore, data compilation in some cases required parental reporting, a possible source of confounding bias and inaccuracies. Several patients received concomitant therapies, making accurate comparisons of response groups more difficult. Finally, documentation of the amount of medication used was not performed as a test of compliance. Clearly, SADBE immunotherapy appears to be a safe, fairly rapid, painless, effective home treatment for warts. Unlike oral or intralesional agents, there are no systemic side effects seen in SADBE-treated patients. Adverse effects with SADBE are local, mild, and rarely limiting. Success of home application depends on good parent education in safe usage and application of SADBE. Data suggest that plantar warts, warts present for less than 2 years, and early response are positive predictors of wart clearing with SADBE immunotherapy. Further studies are required to determine the optimal, least irritating concentration that yields comparable results.

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However, SADBE 0.2% appears to be a relatively nonirritating concentration that only occasionally requires dose-response increases. Most importantly, wart immunotherapy may make possible the induction of long-term immunity to warts via combined cell-mediated and antibody immune responses, theoretically preventing wart recurrence, which is often a source of anxiety and frustration to parents, patients, and physicians alike. This has been especially true for cryotherapy-treated warts, which frequently recur months to weeks after treatment and require repetitive cycles of therapy.45 Further studies are required to evaluate the usefulness of SADBE immunotherapy in the treatment and long-term prevention of this very common pediatric skin infection. REFERENCES 1. Cobb MW. Human papillomavirus infection. J Am Acad Dermatol 1990;22:547-66. 2. Rowson KE, Mahy BW. Human Papova (wart) virus. Bacteriol Rev 1967;31:110-31. 3. Massing AM, Epstein WL. Natural history warts, a two-year study. Arch Dermatol 1963;87:306-10. 4. Lee AKY, Eisinger M. Cell-mediated immunity (CMI) to human wart virus and wart-associated tissue antigens. Clin Exp Immunol 1976;26:419-24. 5. Kienzler JL, Lemoine MTH, Orth G, Jibard N, Blanc D, Laurent R, et al. Humoral and cell-mediated immunity to human papillomavirus type I (HPV-I) in human warts. Br J Dermatol 1983;108: 665-72. 6. Kienzler J-L. Humoral immunity to human papillomaviruses. Clin Dermatol 1985;3:144-55. 7. Pyrhonen S, Johansson E. Regression of warts: an immunologic study. Lancet 1975;1:592-6. 8. Gaspari AA, Zalka AD, Payne D, Menegus M, Bunce LA, Abboud CN, et al. Successful treatment of a generalized human papillomavirus infection with granulocyte-macrophage colony-stimulating factor and interferon gamma immunotherapy in a patient with a primary immunodeficiency and cyclic neutropenia. Arch Dermatol 1997;133:491-6. 9. Gross G, Roussaki A, Papendick U. Efficacy of interferons on bowenoid papulosis and other precancerous lesions. J Invest Dermatol 1990;95:152S-7S. 10. Niimura M. Application of beta-interferon in virus-reduced papillomas. J Invest Dermatol 1990;95:149S-151S. 11. Shiohara T, Hayakawa J, Nagashima M. Interferon gamma as adjuvant therapy for resistant warts. J Am Acad Dermatol 1989; 21:387-91. 12. Siegfried EC. Warts on children: an approach to therapy. Pediatr Ann 1996;25:79-90. 13. Steele K, Shirodaria P, O’Hare MO, Merrett JD, Irwin WG, Simpson DIH, et al. Monochloroacetic acid and 60% salicylic acid as a treatment for simple plantar warts: effectiveness and mode of action. Br J Dermatol 1988;118:537-44. 14. Shelley WB, Shelley ED. Intralesional bleomycin sulfate therapy for warts. Arch Dermatol 1991;127:234-6. 15. Moncada B, Rodriguez ML. Levamisole therapy for multiple warts. Br J Dermatol 1979;101:327-30. 16. Orlow SJ, Paller A. Cimetidine therapy for multiple viral warts in children. J Am Acad Dermatol 1993;28:794-6. 17. Glass AT, Solomon BA. Cimetidine therapy for recalcitrant warts in adults. Arch Dermatol 1996;132:680-2.

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18. Lewis HM. Topical immunotherapy of refractory warts. Cutis 1973;12:863-7. 19. Guhrman-Yahr M, Fernandez J, Convit J. Immunotherapy of disseminated warts with dinitrochlorobenzene. Med Cutan Ibero Lat Am 1976;4:187-93. 20. Buckner D, Price NM. Immunotherapy of verrucae vulgares with dinitrochlorobenzene. Br J Dermatol 1978;98:451-5. 21. Dunagin WG, Millikan LE. Dinitrochlorobenzene immunotherapy for verrucae resistant to standard treatment modalities. J Am Acad Dermatol 1982;6:40-5. 22. Dunagin WG. Use of dinitrochlorobenzene (DNCB) in therapy of warts. J Am Acad Dermatol 1984;10:1069-71. 23. Happle R, Kalveram KJ, Buchner U, Echternacht-Happle K, Goggelmann W, Summer KH. Contact allergy as a therapeutic tool for alopecia areata: application of squaric acid dibutylester. Dermatologica 1980;161:289-97. 24. Swanson NA, Mitchell AJ, Leahy MS, Headington JT, Diaz LA. Topical treatment of alopecia areata. Arch Dermatol 1981;117: 384-7. 25. Happle R, Echternacht K. Induction of hair growth in alopecia areata with DNCB. Lancet 1977;2:1002-3. 26. Case PC, Mitchell AJ, Swanson NA, Vanderveen EE, Ellis CN, Headington JT. Topical therapy for alopecia areata with squaric acid dibutylester. J Am Acad Dermatol 1984;10:447-51. 27. Happle R, Hausen BJ, Wiesner-Menzel L. Diphencyprone in the treatment of alopecia areata. Acta Derm Venereol (Stockh) 1983;63:49-52. 28. Claudy AL, Roche H, Gogue Y. Traitement des verrues multiples et recidivantes par induction d’une hypersensitibilite retardee. Ann Dermatol Venereol 1980;107:551-3. 29. Eriksen K. Treatment of the common wart by induced allergic inflammation. Dermatologica 1980;160:161-6. 30. Naylor MF, Neldner KH, Yarbrough GK, Rosio TJ, Iriondo M, Yeary J. Contact immunotherapy of resistant warts. J Am Acad Dermatol 1988;19:679-83. 31. Wiesner-Menzel L, Happle R. Ruckbildung von plantarwarsen nach behandlung mit diphencyprone. Z Hautkr 1983;58:10803. 32. Iijima S, Otsuka F. Contact immunotherapy with squaric acid dibutylester for warts. Dermatology 1993;187:115-8.

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33. Claudy AL, Roche H.Traitement des verruces multiples et recidivantes par induction d’une hypersensibilite retardee. II. Etude critique de l’utilisation du dibutylester de l’acide squarique. Ann Dermatol Venereol (Paris) 1981;108:765-7. 34. Wilkerson MG, Henkin J, Wilkin JK. Diphenylcyclopropenone: examination for potential contaminants, mechanisms of sensitization, and photochemical stability. J Am Acad Dermatol 1984;11:802-7. 35. Perret CM. Erythema multiforme-like eruptions: a rare side effect of topical immunotherapy with diphenylcyclopropenone. Dermatologica 1990;180:5-7. 36. Wilkerson MG, Henkin J, Wilkin JK, Smith RG. Squaric acid and esters: analysis for contaminants and stability in solvents. J Am Acad Dermatol 1985;13:229-34. 37. Orecchia G, Marelli MA, Perfetti L, Rabbiosi G. Alopecia areata: more on topical sensitizers. Dermatologica 1990;180:57-9. 38. Orecchia G, Malagoli P, Sntagostino L. Treatment of severe alopecia areata with squaric acid dibutylester in pediatric patients. Pediatr Dermatol 1994;11:65-7. 39. Tosti A, Guidetti MS, Bardazzi F, Misciali C. Long-term results of topical immunotherapy in children with alopecia totalis or alopecia universalis. J Am Acad Dermatol 1996;35:199-201. 40. Valsecchi R, Cainelli T, Tornaghi A, Rossi A, Perego GB, Smojver E, et al. Squaric acid dibutylester treatment of alopecia areata. Clin Exp Dermatol 1985;10:233-8. 41. Van der Steen PHM, Boezeman JBM, Happle R. Topical immunotherapy for alopecia areata: reevaluation of 139 cases after an additional follow-up of 19 months. Dermatology 1992; 184:198-201. 42. Choi YS, Han SK, Park YK. The effects of cimetidine on verruca plana juvenilis: clinical trials in six patients. J Dermatol 1993;20: 497-500. 43. Daman LA. Acquired tolerance to dinitrochlorobenzene reversed by cimetidine. Lancet 1977;2:1087. 44. Han R, Breitburd F, Marche PN, Orth G. Linkage of regression and malignant conversion of rabbit papillomas to MHC class II genes. Nature 1992;356:66-8. 45. Bunney MH, Nolan MW,Williams DA. An assessment of methods of treating viral wart by comparative treatment trials based on a standard design. Br J Dermatol 1976;94:667-79.