Published: October 2007

Publications

Osteonecrosis Of The Jaw And Bisphosphonates - Putting The Risk In Perspective

Mark Bolland, David Hay, Andrew Grey, Ian Reid, Tim Cundy

Reprinted from the New Zealand Medical Journal 2006;119(1246) with permission from the New Zealand Medical Association (article available on-line at www.nzma.org.nz/journal/119-1246/2339).

Prescriber Update 28(1): 14-17.
October 2007

Osteonecrosis of the jaw is a poorly understood condition that has recently been associated with the use of potent bisphosphonate treatment.  The prevalence appears to be approximately 1-10% in patients with malignancy treated with very high doses of intravenous bisphosphonates.  In Paget's disease and osteoporosis, where the doses of bisphosphonate used are an order of magnitude lower than the oncology dose, the prevalence appears to be much lower - probably less than 1 in 60,000.  The aim of this article is to put the risks of osteonecrosis of the jaw into context with the benefits of bisphosphonate treatment in these clinical scenarios.

Osteonecrosis of the jaw (ONJ) is a recently recognised (but poorly understood) dental condition that is associated with use of potent bisphosphonate therapy, usually in the context of malignancy.

Recent publicity about ONJ in the lay media in New Zealand, and cautious recommendations by North American dental authorities,¹ have created uncertainty, and in some cases alarm, amongst patients, doctors, and dentists about the safety of bisphosphonates.  Specifically, some dentists are declining to perform dental work in patients who are receiving bisphosphonate therapy for non-malignant skeletal conditions, and some patients are discontinuing or declining effective therapy for osteoporosis because of concern about ONJ.

The aim of this article is to examine the risks and benefits of bisphosphonate treatment in light of the current evidence pertaining to osteonecrosis of the jaw (ONJ).

What is ONJ?

ONJ is characterised by exposed areas of jawbone, more commonly affecting the mandible than the maxilla.^2-5  Most cases are precipitated by tooth extraction or other dental surgery, but 25% occur without obvious preceding oral trauma.³  The problem may progress to bone necrosis and sinus or fistula formation, but its natural history is not known.  While pain is a typical presenting feature, approximately 33% of cases are asymptomatic.  Plain X-rays may be normal in the early stages, but later show poorly defined osteolysis with or without sequestrum formation.  Histology has been reported as showing necrotic bone, bacterial debris and granulation tissue.^3-5

The clinical syndrome of ONJ was first described in association with bisphosphonate use by Marx in 2003.²  The pathophysiology of ONJ is unknown, however, it is important to emphasise that ONJ appears to be unrelated to avascular osteonecrosis of long bones, or to radiation-induced osteonecrosis.

Previously, the bisphosphonate-associated disorder had only been observed in the jaw, however, one patient has been recently reported with ONJ of the jaw and auditory canal.⁶  It is hypothesised that high doses of bisphosphonates suppress bone remodelling in the jaw to a degree that impairs the ability to repair microdamage induced by oral trauma and/or infection.  The role of other potential risk factors such as chemotherapeutic agents, corticosteroids, poor oral health, and other dental comorbidities has not been established.⁴  The optimal management of established disease is uncertain at present but pain and infection control, conservative debridement of necrotic bone, and bisphosphonate withdrawal are recommended.⁵

Who receives bisphosphonates?

Before considering the incidence of ONJ in bisphosphonate-treated patients, it is important to emphasise that these agents are prescribed to two groups of patients: one with non-malignant skeletal diseases, in particular osteoporosis and Paget's disease of bone; the other with cancer-related skeletal disease, most commonly metastatic breast cancer and multiple myeloma.

Important differences exist between these patient groups in the dose of bisphosphonate prescribed, in concomitant medical therapies, and in the risk of developing ONJ (see below).  Thus, patients with malignant skeletal disease typically receive 12-fold higher doses of bisphosphonates (4mg intravenous zoledronate or 90mg intravenous pamidronate monthly, alendronate not used) than patients with non-malignant skeletal disease (osteoporosis, alendronate 70mg weekly, intravenous pamidronate 90mg annually, zoledronate 4-5mg annually; Paget's disease, intermittent courses of treatment every 2-3 years with alendronate 40mg daily for 6 months, intravenous pamidronate 60-180mg, or intravenous zoledronate 4-5mg).  In addition, patients with cancer are typically receiving cytotoxic agents that may influence general and oral health.

How common is bisphosphonate-associated ONJ?

A recent review summarised published cases of ONJ.⁵ 95% of the reported cases of ONJ occurred in patients with malignant skeletal disease.  Of the three cases of ONJ that have occurred in association with bisphosphonate treatment for Paget's disease, 2 were prescribed inappropriately high doses of bisphosphonates (alendronate 40mg/day for 5 years, pamidronate 90mg monthly for 18 months).  In this review, 15 cases of ONJ were reported in patients receiving bisphosphonate treatment for osteoporosis.⁴

By March 2006, approximately 170 cases worldwide of ONJ in association with alendronate had been reported to the manufacturer (Merck).⁷  There are few clinical details available for the majority of these cases.  These cases have occurred on a background of very extensive use of bisphosphonates for osteoporosis and Paget's disease in the past decade.

In 2004, it was estimated that there had been approximately 20 million patient-years of alendronate treatment for these conditions.⁸  It is possible that under-reporting of cases has occurred, but this would have to be very substantial to significantly alter the very low incidence.

No cases of ONJ were reported in randomised controlled trials of alendronate, risedronate or ibandronate that collectively included more than 60,000 patients treated for at least 2 years.  Therefore, while the incidence of ONJ in patients treated with bisphosphonate for Paget's disease and osteoporosis is difficult to determine, it is very likely to be less than 1/60,000 and is perhaps as low as 1/200,000.

The incidence of ONJ in patients receiving high-dose bisphosphonate treatment for metastatic malignancy is much higher.  Estimates range up to 10%,⁵ but the best available data, collected retrospectively on 4000 patients from a single institution, suggest that about 0.85% of these patients are affected.⁹

Patients with ONJ in this setting have all had metastatic malignancies, most commonly multiple myeloma or breast cancer, and often have been receiving chemotherapeutic agents, or corticosteroids, or had other dental comorbidities.⁴  The roles of these possible predisposing factors have not yet been determined.

Balancing the risks

Osteoporosis - Bisphosphonates are the only available agents of proven effectiveness for the treatment or prevention of osteoporosis in New Zealand (oestrogen replacement therapy is also effective¹⁰ but not widely used).

Alendronate treatment reduces the risk of vertebral and non-vertebral fractures by about 50%.¹¹  The absolute benefit in fracture prevention from treatment with alendronate depends on the baseline risk of sustaining a fracture.  For a 65-year-old woman with a bone density T score of -2.5 and no other clinical risk factors for osteoporotic fracture, the estimated probability of sustaining a hip fracture in the next 10 years is 5.9%.¹²  In this situation the number of women that need to be treated (NNT) with a course of alendronate to prevent one hip fracture is 35.

For an 80-year-old woman with a previous osteoporotic fracture and a bone density T score of < -2.5, the estimated probability of sustaining a hip fracture in the next 10 years is 45%.¹²  In this situation, the NNT is 4.5.  In comparison, the number of women that need to be treated with a course of alendronate to cause one case of ONJ - the number needed to harm (NNH) - is very likely to be at least 60,000.

Osteoporotic fractures are not trivial events.  Hip fracture is associated with a 25% risk of death within 12 months of the event, and a high risk of decreased independence in those who survive.^13,14  Clearly, the balance of risk and benefit favours alendronate treatment for osteoporotic patients.  In addition, the NNH is sufficiently high that any form of screening or preventative dental treatment is highly unlikely to be cost-effective or produce a meaningful reduction in ONJ incidence.

Paget's disease - Bisphosphonates are a highly effective treatment for Paget's disease.^15,16  Patients with Paget's disease typically receive infrequent (every 2-5 years) courses of bisphosphonates, such that the overall drug exposure is less than occurs in patients with osteoporosis.  It is therefore very likely that the risk of ONJ in patients with Paget's disease treated with conventional doses of bisphosphonates is even lower than that in patients with osteoporosis.

Metastatic malignancy - Bisphosphonates reduce pain from skeletal metastases (NNT at 4 weeks is 11, NNT at 12 weeks is 4).¹⁷  In multiple myeloma, bisphosphonates reduce pathological vertebral fractures by 41% with a corresponding NNT of 10.¹⁸

In patients with breast cancer metastatic to bone, bisphosphonates reduce the number of skeletal events by 17%, the rate of skeletal events by 29%, reduce pain, and may increase quality of life.  The NNT to prevent one skeletal event is 9.¹⁹ In prostate cancer with bone metastases, zoledronate reduced skeletal events by 25% over 18 months in one trial of men with androgen-insensitive prostate cancer (NNT = 9).²⁰  No other bisphosphonate has been shown to be effective in metastatic prostate cancer.²⁰

Treatment with bisphosphonates has not been demonstrated to prolong survival in any of these malignancies.^18-20  Thus, in the treatment of metastatic malignancy, the absolute benefit from treatment (NNT 4-10 depending on endpoint) is much closer to the absolute harm from treatment (NNH 10-120).  In this situation, screening or preventative dental treatment prior to initiation of bisphosphonate treatment may be appropriate and guidelines for dentists seeing such patients have been published.⁵  The efficacy of the recommended prevention strategies has not been evaluated.

Currently, it is not known whether lower doses of bisphosphonates than are currently prescribed are effective in reducing cancer-related skeletal morbidity.  If, as seems likely, there is a dose-response relationship between bisphosphonate treatment and risk of ONJ, the use of lower doses of bisphosphonates for treatment of skeletal metastases may be associated with a lower risk of ONJ.

How should we approach the problem of ONJ?

Current evidence suggests that the risk of ONJ in patients with cancer in whom high dose bisphosphonate therapy is being commenced is high enough to justify the screening and intervention strategies recommended by various dental authorities.^1,5  It should be acknowledged, however, that at present such strategies have not been demonstrated to influence the incidence of ONJ.

Current evidence suggests that the risk of ONJ in patients with non-malignant skeletal conditions who are receiving conventional doses of bisphosphonates is so low that (a) systematic screening or prevention programmes and (b) withholding dental procedures are not justified in this setting.

Adopting an ultra-conservative approach in these patients runs the risk of denying necessary dental care to patients receiving bisphosphonates, and denying patients with dental disease an effective therapy for osteoporosis or Paget's disease.

Recommendations for dental care in patients receiving bisphosphonates for non-malignant skeletal disease have recently been developed.²¹  Routine dental care, in the form of an annual examination, should be encouraged in all patients.

Conflict of interest statement: None of the authors have a conflict of interest.

Author information:
Mark Bolland, Research Fellow, Department of Medicine, University of Auckland.
David Hay, Oral Medicine Specialist, Oral Health Regional Service, Auckland District Health Board.
Andrew Grey, Associate Professor of Medicine, Department of Medicine, University of Auckland.
Ian R Reid, Professor of Medicine, Department of Medicine, University of Auckland.
Tim Cundy, Professor of Medicine, Department of Medicine, University of Auckland; Auckland.

Correspondence: Mark Bolland, Osteoporosis Research Group, Department of Medicine, University of Auckland, Private Bag 92 019, Auckland 1020.  Fax: (09) 373 7677; email: m.bolland@auckland.ac.nz

References

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