Secondary actinomycosis in a recurrent odontogenic keratocyst: A clinicopathological diagnostic challenge with 5-year follow-up.

OKC is an odontogenic developmental cyst with a significant risk of recurrence. Secondary infections of the lesion with Actinomyces organisms are rare and may pose a dilemma in managing the recurrent lesion. A 20-year-old male patient reported to the outpatient department with a radiolucent multilocular lesion of the posterior right side of the mandible. A diagnosis of OKC was made based on histopathology, and a conservative approach involving decompression and marsupialisation with subsequent enucleation of the cyst and peripheral ostectomy was planned. The lesion healed without any complications. After one year, swelling occurred along with a radiolucent lesion in the same area. Re-examination revealed a case of recurrent OKC with cortical expansion and sequestration. Resurgery revealed a lesion with basophilic filamentous bacterial colonies, eosinophilic peripheral clubs with a sulfur granule, and marked inflammation, indicating secondary actinomycotic infection rather than colonization. Aerobic and anaerobic cultures were done. Postoperatively, the patient received antimicrobial therapy consisting of intravenous clindamycin for 7 days, followed by oral amoxicillin-clavulanate for 4 weeks and metronidazole for 7 days. followup was performed clinically and radiographically, with gradual improvement and healing of the disease without recurrence for 4 years after treatment of the recurrent lesion, constituting 5 years of followup from the first diagnosis. This case highlights the importance of re-evaluation through repeated histopathological examination of the recurrent OKC, especially when inflammatory or destructive changes are present.