Sir, actinomycotic osteomyelitis is rare, however, it is important to retain a high index of suspicion for this infection. Diagnosis can be delayed and difficult due to the atypical presentation of infection, long culture times and difficulty isolating actinomyces. Fewer than 50% of cultures from actinomyces-related infections manage to isolate a species; as a result many diagnoses rely on histopathological visualisation of actinomyces over microbiological isolation.1

A fit and healthy 33-year-old male attended our oral surgery unit with a history of tightness in his left jaw and no other symptoms.

On examination there were remnants of a sinus tract in the mandibular left second molar (37) region, with no paraesthesia, drainage or swelling. The 37 had been extracted 20 years previously. An orthopantomogram showed a radiolucent lesion extending from the alveolar ridge of the 37 region to the cortex of the lower border of the mandible (Fig. 1). Cone beam CT revealed there was erosion of the buccal cortical plate and the bone surrounding the inferior dental canal (Fig. 2).

Fig. 1
figure 1

Orthopantomogram (OPG) showing a radiolucent lesion between the left mandibular first (36) and second molar (38), extending from the alveolar crest to the cortex of the lower border of the mandible

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Fig. 2
figure 2

Dental cone beam computed tomography (CBCT). Axial view of mandible showing radiolucent lesion in the 37 region with erosion of the left buccal cortical plate. The lesion had an intimate association with the inferior dental canal with no intervening bone

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Histopathological analysis of the lesion following curettage and stent placement under local anaesthetic showed large colonies of actinomyces-like bacteria present indicating actinomycotic osteomyelitis. However, initial microbiology culture did not isolate actinomyces species. A second microbiological culture using 16s rDNA sequencing was carried out following stent placement which isolated Eikenella corrodens but again no actinomyces.

Actinomyces osteomyelitis was confirmed from the clinical history, radiographs and histopathology. Management is typically surgical debridement and long-term intravenous penicillin antibiotics for two to six weeks, followed by oral penicillin 2-4 g per day for six to 12 months. However, antibiotic regimes should be tailored to the patient and reviewed regularly.2 Ceftriaxone was given intravenously in this case to target both actinomyces and E corrodens. Extended antibiotic exposure is recommended as actinomyces have a slow rate of lysis compared to other bacteria, and the risk of developing penicillin resistant actinomyces is considered low. 2

Actinomyces-related infections are always polymicrobial, relying on mutualistic relationships with other oral commensals to create a favourable environment for survival.3 In this case, stent placement prior to the second microbial sample likely shifted the balance to a more advantageous environment for another opportunistic gram-negative anaerobe: Eikenella corrodens.

Actinomyces-related infection was not listed as a differential diagnosis, likely resulting in a shorter incubation time and a storage environment not conducive to the culture of actinomyces, which requires a minimum seven days compared to the normal three to five days for anaerobic bacteria.3

Due to the chronic burrowing, slow growing nature of these infections, it is possible that the extraction socket of the 37 never fully healed following extraction 20 years previously and the diagnosis had been missed.