D2.302 - Non - immediate hypersensitivity to oxybutynin, first confirmed case with lymphocyte transformation test

Oxybutynin is an anticholinergic drug that acts as a muscarinic acetylcholine receptor antagonist. It is mainly used for treatment of overactive bladder syndrome. Local skin adverse reactions to topical oxybutynin are frequent, yet none have been rigorously studied up to date.

We present a case of a 62-year-old female with history of urinary incontinence in treatment with commercial oxybutynin transdermal patches, with application of transdermal patches every 3 days in abdominal and gluteal areas. 2 months after continuous treatment and 1 hour after the application of the 24^th patch in right gluteal area, the patient presents a localized, itchy erythematous plaque overlapping dimensions of the patch. No other accompanying symptoms. Furthermore, the patient mentions previous episodes of erythema in other application areas. The clinical picture resolved with oral antihistamine and topical corticosteroid treatment, with no residual lesion. Consequently, treatment with oxybutynin patches was suspended and replaced by oral mirabegron and the patient was sent to the Allergology department for subsequent studying.

Suspecting a delayed hypersensitivity drug induced reaction, patch testing with true-test was performed, supplemented with acrylates. A sample of commercial patch was also placed under occlusion for 48 hours on normal back skin. Readings 24 and 48 hours after patch application resulted positive for only the sample patch, resulting negative for both acrylates and true-test patching.

In addition to all this, a Lymphocyte Transformation Test (LTT) for oxybutynin (concentrations 0.001 mg/mL, 0.001 mg/mL, 0.01 mg/mL, 0.1 mg/mL), with positive results, was performed to confirm hypersensitivity to the drug itself and rule out in combination with the results of patch testing any other causing agent, as well as to further investigate the immune mechanism involved, suspected to be a delayed hypersensitivity T lymphocyte cell mediated reaction. 

CONCLUSION

We present a delayed cutaneous reaction to oxybutynin, confirmed by LTT. Although in vitro tests, particularly LTT, have yet to be standardized and validated, they can serve as a valuable tool in clarifying the hypersensitivity mechanisms involved. LTT can be especially useful in identifying and confirming non – immediate reactions and their culpable agents when combined with relevant clinical information and other available diagnostic tests.