Validity of an algorithm to identify osteonecrosis of the jaw in women with postmenopausal osteoporosis in the Danish National Registry of Patients

Henrik Gammelager,¹ Claus Sværke,¹ Sven Erik Noerholt,² Bjarne Neumann-Jensen,³ Fei Xue,⁴ Cathy Critchlow,⁴ Johan Bergdahl,⁵ Ylva Trolle Lagerros,⁵ Helle Kieler,⁵ Grethe S Tell,⁶ Vera Ehrenstein<sup>1

1</sup>Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; ²Department of Oral and Maxillofacial Surgery, Aarhus University Hospital, Aarhus, Denmark; ³Department of Oral and Maxillofacial Surgery, Aalborg University Hospital, Aalborg, Denmark; ⁴Center for Observational Research, Amgen Inc., Thousand Oaks, CA, USA; ⁵Center for Pharmacoepidemiology, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden; ⁶Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway

Background: Osteonecrosis of the jaw (ONJ) is an adverse effect of drugs that suppress bone turnover – for example, drugs used for the treatment of postmenopausal osteoporosis. The Danish National Registry of Patients (DNRP) is potentially valuable for monitoring ONJ and its prognosis; however, no specific code for ONJ exists in the International Classification of Diseases 10th revision (ICD-10), which is currently used in Denmark. Our aim was to estimate the positive predictive value (PPV) of an algorithm to capture ONJ cases in the DNRP among women with postmenopausal osteoporosis.
Methods: We conducted this cross-sectional validation study in the Central and North Denmark Regions, with approximately 1.8 million inhabitants. In total, 54,956 women with postmenopausal osteoporosis were identified from June 1, 2005 through May 31, 2010. To identify women potentially suffering from ONJ, we applied an algorithm based on ICD-10 codes in the DNRP originating from hospital-based departments of oral and maxillofacial surgery (DOMS). ONJ was adjudicated by chart review and defined by the presence of exposed maxillofacial bone for 8 weeks or more, in the absence of recorded history of craniofacial radiation therapy. We estimated the PPV for the overall algorithm and for each separate ICD-10 code used in the algorithm.
Results: Charts were obtained and reviewed for all 60 women with an ICD-10 code potentially representing ONJ. Nineteen potential ONJ cases were confirmed, corresponding to an overall PPV of 32% (95% confidence interval: 20%–45%).
Conclusion: Among women with postmenopausal osteoporosis, only about one-third of the potential ONJ cases identified by our ICD-10 based algorithm were confirmed by medical chart review, despite the restriction to patients treated at DOMS. To capture true ONJ cases among women with postmenopausal osteoporosis, alternative approaches are needed.

Keywords: bisphosphonate-associated osteonecrosis of the jaw, International Classification of Diseases, osteonecrosis of the jaw, osteoporosis, registries, validity