Paget's disease of bone: treatment philosophy for the twenty-first century

ZOLEDRONIC ACID THERAPY OF PATIENTS WITH PAGET DISEASE OF BONE RESISTANT TO OR WITH UNSUSTAINED REMISSION FOLLOWING PRIOR BISPHOSPHONATE THERAPY

OBJECTIVE

To evaluate the effect of zoledronic acid (ZA) in patients with Paget disease (PD) who had not had a biochemical remission with prior bisphosphonate therapy or had a remission ≤12 months.

METHODS

The effects of ZA therapy were studied in 14 patients aged 54 to 90. Serum alkaline phosphatase (ALP) levels were elevated to at least 40% above the normal reference range, and glomerular filtration rates (GFRs) were ≥40 mL/minute. ZA (5 mg) was infused over 15 minutes. ALP and urine N-telopeptide/creatinine (NTx/Cr) were obtained before therapy and at 3, 6, 9, and 12 months, and thereafter at 4-month intervals.

RESULTS

At baseline, ALP ranged from 141 to 1,009 U/L. In 13 patients, ALP fell to normal following ZA administration. Remissions occurred in 9 patients who had not previously had a remission. Remissions varied from 12 to 60 months and were more prolonged in 4 patients with prior remissions ≤12 months. ZA failed to induce a remission in 1 patient. Ten to 12 days after therapy in 3 asymptomatic patients, serum calcium levels fell to 7.9, 8, and 8.3 mg/dL. Other than flu-like symptoms in 3 patients after ZA infusion, there were no other adverse effects.

CONCLUSION

Therapy with ZA induced remissions in 13/14 patients and induced more prolonged remissions in patients who previously had remissions ≤12 months. The lack of remission in 1 patient despite 2 courses of therapy is evidence of a continuing therapeutic challenge for some patients with a more resistant form of PD.

The spine in Paget's disease

Paget's disease (PD) is a chronic metabolically active bone disease, characterized by a disturbance in bone modelling and remodelling due to an increase in osteoblastic and osteoclastic activity. The vertebra is the second most commonly affected site. This article reviews the various spinal pathomechanisms and osseous dynamics involved in producing the varied imaging appearances and their clinical relevance. Advanced imaging of osseous, articular and bone marrow manifestations of PD in all the vertebral components are presented. Pagetic changes often result in clinical symptoms including back pain, spinal stenosis and neural dysfunction. Various pathological complications due to PD involvement result in these clinical symptoms. Recognition of the imaging manifestations of spinal PD and the potential complications that cause the clinical symptoms enables accurate assessment of patients prior to appropriate management.

Zoledronic acid in the treatment of Paget's disease and other benign bone disorders

Zoledronic acid is a potent bisphosphonate widely used to counteract cancer-related bone loss. Once-yearly or even less frequent doses may be an effective therapy for benign bone disorders and may also result in improved compliance and tolerability. Data from two Phase III clinical trials have demonstrated the efficacy and safety of zoledronic acid in the treatment of Paget's disease of bone. Other studies have provided preliminary evidence for the utility of zoledronic acid in osteoporosis and other benign bone disorders. The major adverse effects associated with zoledronic acid infusions are transient flu-like symptoms. Ongoing clinical trials will provide key data on the ability of this agent to treat osteoporosis and prevent fractures in high-risk patients and on its long-term safety profile.

The mechanism of hearing loss in Paget's disease of bone

OBJECTIVES/HYPOTHESIS

The mechanism of hearing loss (HL) in Paget's disease of bone was investigated. The present study was a systematic, prospective, controlled set of clinical investigations to test the hypothesis that there is a general underlying mechanism of HL in Paget's disease of bone and to gain additional insights into the auditory and otologic dynamics of this disease. Specific questions were 1) whether the mechanism is cochlear or retrocochlear and 2) whether the bone mineral density of the cochlear capsule is related to hearing levels.

STUDY DESIGN

Several double-blinded, cross-sectional, prospective, correlational studies were conducted in a population of elderly human subjects with skull involvement with Paget's disease versus a control population of elderly subjects free of Paget's disease. Demographic and clinical data were recorded. Longitudinal observations were made in subjects under treatment.

METHODS

Subjects were recruited from a Paget's disease clinic. Pure-tone auditory thresholds, word recognition, and auditory brainstem responses (ABRs) were recorded. The dimensions of the internal auditory canals were measured using computed tomographic (CT) images and digital image analysis. The precision, accuracy, and temporal stability of methods to measure the bone mineral density of the cochlear capsule and an adjacent area of nonotic capsule bone were validated and applied. Correlations were sought between hearing levels and cochlear capsule bone mineral density.

RESULTS

ABRs were recorded in 64 ears with radiographically confirmed Paget's disease involving the skull. Responses were absent in eight ears, all of which had elevated high pure-tone thresholds. ABRs were interpreted as normal in 56 ears; none were abnormal. The mid-length diameter and minimum diameter of the internal auditory canal of 68 temporal bones from subjects with Paget's disease were found to have no statistically significant relationship to hearing thresholds. The Pearson product-moment correlation coefficients (age- and sex-adjusted) in the group with Paget's disease involving the temporal bone were -0.63 for left ears and -0.73 for right ears for high-frequency air conduction pure-tone thresholds (mean of 1, 2, and 4 kHz) versus cochlear capsule density. Correlation coefficients (age- and sex-adjusted) between cochlear capsule density and air-bone gap (mean at 0.5 and 1 kHz) for the affected group were -0.67 for left ears and -0.63 for right ears. All correlations between hearing thresholds and cochlear capsule density in pagetic subjects were significant at P <.001. The regressions were consistent throughout the ranges of hearing level. There were no significant correlations between cochlear capsule mean density and hearing level in the volunteer subjects.

CONCLUSIONS

The evidence supports the existence of a general, underlying, cochlear mechanism of pagetic HL that is closely related to loss of bone mineral density in the cochlear capsule. This mechanism accounts well for both the high-frequency sensorineural HL and the air-bone gap. Early identification, radiographic diagnosis of temporal bone involvement, and vigorous treatment with third-generation bisphosponates are important to limit the development and progression of pagetic HL.

Bisphosphonate resistance in Paget's disease of bone

OBJECTIVE

To determine whether resistance to one bisphosphonate predicts resistance to another bisphosphonate.

METHODS

One hundred patients with Paget's disease were treated with intravenous (IV) pamidronate. The initial dose was 120 mg, followed by further doses of 240 mg, until either biochemical remission was achieved or a total dose of 1 gm was given. Biochemical remission was defined as an alkaline phosphatase level within the reference range. Patients whose disease failed to respond to pamidronate were then treated with alendronate for 6 months. Patients whose disease failed to respond to alendronate were given either tiludronate for 3 months, or clodronate for 6 months.

RESULTS

Sixteen of the 100 patients treated with pamidronate failed to achieve a biochemical response despite a cumulative dose of 1 gm. Of the 16 nonresponders, 1 died of an unrelated cause, and the remaining 15 patients were treated with alendronate. In 2 of these patients, the treatment was changed to another bisphosphonate because of gastrointestinal intolerance to alendronate. Of the remaining 13 patients, 9 (69%) achieved full biochemical remission. In 4 other patients, both pamidronate and alendronate therapy were unsuccessful (1 patient responded to tiludronate, tiludronate therapy was unsuccessful in 1, clodronate was unsuccessful in 1, and 1 patient elected to receive no further treatment). Of the 2 patients who could not receive alendronate because of gastrointestinal intolerance, 1 achieved normalization with tiludronate, and a repeat course of pamidronate was unsuccessful in the other. In total, 73% of patients in whom initial treatment with IV pamidronate was unsuccessful responded to a change in bisphosphonate treatment.

CONCLUSION

Failure to achieve biochemical normalization is likely to be specific to the individual drug rather than indicative of bisphosphonate class resistance.