Topical Sirolimus Gel for the Treatment of Superficial Microcystic Lymphatic Malformations in Pediatric Patients: A Case Series.

Background: Superficial microcystic lymphatic malformations (MLMs) can cause persistent lymphatic leakage, bleeding, recurrent infection, and disfigurement. Conventional treatments, including surgical excision and sclerotherapy, are invasive and may result in scarring or incomplete resolution. Topical sirolimus may offer a localized, mechanism-based alternative with potentially limited systemic exposure. Objective: To describe the clinical response and safety of 0.2% topical sirolimus gel in pediatric patients with superficial MLMs. Methods: This retrospective case series included three pediatric patients with clinically and radiologically confirmed superficial MLMs. Patients received 0.2% topical sirolimus gel twice daily for 6 months. Treatment response was assessed by two independent dermatologists based on clinical examinations and serial clinical photographs, including changes in lesion size, color, thickness, bleeding, exudation, pain, pigmentation, and surface texture. Improvement was categorized as none (0%), minimal (1-25%), moderate (26-50%), or marked (>50%). Safety assessments included local and systemic adverse events and serum sirolimus concentrations. Results: All three patients were classified as having marked improvement (>50%), with reductions in lesion size and thickness, fading of pigmentation, decreased lymphatic leakage, and improvement in surface texture. One patient showed near-complete regression after 6months of treatment. The earliest clinical response was documented 10 days after treatment initiation in one patient. Local adverse events included transient stinging, erythema, pruritus, xerosis, and desquamation and were managed with supportive care or resolved spontaneously. Serum sirolimus concentrations measured at the assessed time points were consistently< 3.5 ng/mL in all three patients, well below the lower limit of quantification (LLOQ) and far lower than the therapeutic trough concentrations (4-12 ng/mL) associated with oral sirolimus therapy. Conclusion: In this three-patient case series, 0.2% topical sirolimus gel was associated with greater than 50% clinical improvement and predominantly mild local adverse events. Larger controlled studies using standardized and independently assessed outcomes are needed to establish efficacy and long-term safety.