Mandibular Actinomycosis Disguised as a Periapical Lesion.

Actinomycosis is a rare chronic suppurative granulomatous disease caused by commensal bacteria of Actinomyces species. We report an unusual case of a 20-year-old male patient presenting with pain and swelling to the right lower posterior teeth for a few months. Radiographs revealed a well-defined osteolytic lesion extending from the periapical region of the right mandibular first premolar to the right mandibular second molar. Based on the clinical history of symptoms, a presumptive diagnosis of more commonly appearing jaw lesions like odontogenic cyst/tumor was made. Incision biopsy resulted in an unexpected diagnosis of Actinomycosis, confirmed with Gram stain and Gomori's Methenamine Silver stain. The patient was treated with long-term antibiotics, and follow-up showed a positive response. This article emphasizes the role of histopathology in avoiding the misdiagnosis of such cases.