Actinomyces in infected osteoradionecrosis--underestimated?

Infected osteoradionecrosis (IORN) is a severe complication of radiation therapy for head and neck cancer. Infected osteoradionecrosis can lead to fracture and often requires subsequent jaw resection. It is known that irradiated bone is highly susceptible to infections, mainly with Candida species and cariogenic bacteria. Only very few data exist on Actinomyces in IORN. The study population consisted of 31 patients (7 female, 24 male; median age, 58.3 years). All patients exhibited clinical and radiological signs of IORN (infection, mucosa or skin fistula, and sequestrated bone). To detect Actinomyces colonies, histological examination was performed using several staining procedures (hematoxylin-eosin, Gram, Grocott, periodic acid-Schiff). In addition, a semi-nested polymerase chain reaction (PCR) approach was designed targeting the 16S ribosomal RNA gene. We found prominent Actinomyces colonies in 20 (64.5%) of 31 patients. Most of these lesions were localized in the mandible (16/20). Most interestingly, Actinomyces were almost exclusively found attached to the necrotic bone. PCR testing confirmed the presence of Actinomyces-specific DNA sequences (Actinomyces israelii). We show that Actinomyces is considerably more frequent in IORN than previously demonstrated. We suggest that these organisms are involved in the chronic, nonhealing inflammatory processes and the purulent discharge, which are known as characteristics of IORN. It remains to be investigated whether Actinomyces could be involved in the osteolytic mechanisms. From the histopathologic perspective, detection of Actinomyces is important because these bacteria have been shown to be associated with prolonged treatment duration.