Fibrous dysplasia of mandible—Report of a case presenting with a rare clinical course

Gnathic fibrous dysplasia (FD) and chronic diffuse osteomyelitis (CDO) are independent disease states which have overlapping clinical and radiographic characteristics. Diagnosis is crucial because of the different treatments needed for these clinical conditions. We report here a case of FD of the left mandible which followed a rare clinical course and the initial clinical symptoms and radiographic examination were misinterpreted as indicating CDO. A 28-year-old Japanese male was referred to our hospital due to a dull intermittent pain of the left mandibular molars in April 2002. From the clinical and radiographic examination results, we suspected CDO. Antibiotic treatment produced a remission of these symptoms and periodical follow-up was performed in another hospital. In March 2007 the patient returned with firm swelling in the left cheek region. Panoramic radiographic and CT examination revealed remarkable bony expansion with a thickened cortex and diffuse “smoky mottled” lucent-radiopaque appearance in the left molar region of the mandible. We suspected fibro-osseous lesions of the mandible and surgical reduction was performed in January 2008. Histological examination revealed fibrous and bone tissue proliferation along with the chronic inflammatory lesions and an absence of cortical bone. Mutational analysis demonstrated guanine nucleotide binding protein, alpha atimulating activity polypeptide (GNAS) mutations, resulting in a final diagnosis of FD. Chronic inflammation may complicate the diagnosis of FD of the jaw. The detection of GNAS mutations may provide a useful adjunct to conventional histopathological diagnosis in difficult cases.