Usefulness of biochemical markers of bone turnover in assessing response to the treatment of paget’s disease

Bone Vol. 29, No. 5 November 2001:447– 452

Usefulness of Biochemical Markers of Bone Turnover in Assessing Response to the Treatment of Paget’s Disease ˜ ABENS,2,3 P. PERIS,3 S. VIDAL,4 I. ROS,3 A. MONEGAL,3 J. L. BEDINI,1 L. ALVAREZ,1,2 N. GUAN 1 ˜ OZ-GOMEZ,2,3 and A. M. BALLESTA1 R. DEULOFEU, F. PONS,4 J. MUN 1

Service of Clinical Biochemistry, Hospital Clinic, University of Barcelona, Barcelona, Spain Metabolic Bone Diseases, Institut d’Investigacions Biome`diques August Pi i Sunyer (IDIBAPS), Barcelona, Spain Services of 3Rheumatology and 4Nuclear Medicine, Hospital Clinic, University of Barcelona, Barcelona, Spain 2

duced by treatment. (Bone 29:447– 452; 2001) Elsevier Science Inc. All rights reserved.

The aim of this study was to investigate the usefulness of biochemical markers of bone turnover for monitoring treatment efficacy of Paget’s disease of bone, and also to evaluate the utility of biological variation data in choosing the best markers for assessment of biochemical response to therapy. Thirty-eight patients with Paget’s disease were included in a prospective study. All received 400 mg/day of oral tiludronate for 3 months. In 31 patients that completed treatment, biochemical markers were measured at baseline and at 1 and 6 months after treatment ended. In serum we determined the levels of total alkaline phosphatase (tAP), bone alkaline phosphatase (bAP), procollagen type I N-terminal propeptide (PINP), and C-terminal telopeptide of type I collagen (sCTx). Urine samples were analyzed for hydroxyproline (Hyp) and for C- and N-terminal telopeptides of type I collagen (CTx and NTx, respectively). Quantitative bone scintigraphy was performed at baseline and at 6 months after discontinuation of therapy. A ratio for monitoring response to treatment was obtained for each marker. This ratio reflected the size of treatment response of the marker in relation to the value of its critical difference. Thus, ratio values of >1 indicated a significant decrease of the marker after therapy. In addition, response to therapy was evaluated according to disease activity. Mean values of all markers of bone turnover decreased significantly after therapy. Serum bAP and PINP and urinary NTx showed the highest percentage reduction (between 58% and 68%). Furthermore, serum bAP and PINP showed the highest ratios for monitoring changes induced by treatment, followed by serum tAP and urinary NTx. sCTx and urinary CTx as well as Hyp showed mean ratios for monitoring changes of <1, indicating a low sensitivity for monitoring treatment. Patients with polyostotic disease showed a continuous decrease in mean values for all markers at 6 months from the end of therapy, whereas, in monostotic patients, there was a trend toward increased levels at this timepoint. In conclusion, serum bAP and PINP were the most sensitive markers for monitoring treatment efficacy in Paget’s disease, although serum tAP and urinary NTx were also sensitive markers for monitoring changes. Data on biological variation are useful for assessing actual changes in-

Key Words: Bisphosphonates; Variability; Critical difference; Procollagen type I N-terminal propeptide (PINP); Bone alkaline phosphatase (bAP); N-terminal telopeptide of type I collagen (NTx). Introduction Paget’s disease of bone is a chronic progressive disorder of the adult skeleton in which localized areas of bone undergo increased and disordered bone remodeling. Normal bone is replaced by a disorganized, enlarged, and weakened osseous structure that is prone to pain, deformity, and fracture.20 Some years ago, only symptomatic patients were treated. However, in recent years, the therapeutic strategy has changed and not only patients with pain or other symptoms, but also young patients, those with increased risk of complications because of the location of involved bones, and patients with evidence of active disease, as shown by elevated levels of biochemical markers of bone turnover, have been considered candidates for treatment.7,13 Likewise, it is important to monitor effectively the disease activity and the degree of disease suppression induced by the antipagetic therapy, and to ascertain the suitability of new courses of treatment aimed at preventing future complications. Markers of bone turnover have been shown to be useful tools in the assessment of Paget’s disease activity, but their clinical usefulness clearly depends on the marker employed. Thus, it has been shown previously that serum procollagen type I N-terminal propeptide (PINP) or bone alkaline phosphatase (bAP) and urinary N-terminal telopeptide of type I collagen (NTx) provide the best biochemical profile for assessing Paget’s disease activity, particularly in low-activity or monostotic disease.2 Nevertheless, the theoretical advantages of these markers compared with traditional markers, such as serum total alkaline phosphatase (tAP) or urinary hydroxyproline (Hyp), in monitoring patients on therapy are unknown. This point is especially important because biological variations among all bone markers are different, thus influencing their value at follow-up assessment. Therefore, the aims of this study were to compare the usefulness of the traditional (serum tAP and urinary Hyp) and new markers of bone turnover (serum bAP, PINP, and C-terminal telopeptide of type I collagen, sCTx, as well as urinary Cterminal telopeptide of type I collagen [CTx and NTx]) in monitoring treatment response in patients with Paget’s disease,

Address for correspondence and reprints: Luisa Alvarez, Ph.D., Servicio Bioquı´mica Clı´nica, Hospital Clinic, C/Villarroel 170, 08036 Barcelona, Spain. E-mail: [email protected] © 2001 by Elsevier Science Inc. All rights reserved.

© 2001 by

447

8756-3282/01/$20.00 PII S8756-3282(01)00592-0

448

L. Alvarez et al. Treatment response in Paget’s disease

and to evaluate the utility of the biological variation data for choosing the best markers.

Bone Vol. 29, No. 5 November 2001:447– 452 Table 1. Analytical and biological variation of biochemical markers of bone turnover

Marker

Interassay variation (CVa) (CV%)

Within-subject variation (CVi) (CV%)

Between-subject variation (CVg) (CV%)

Values for critical differences (%)

Serum tAP bAP PINP sCTx

1.5 7.5 7.4 9.2

12.4 4.9 10 12.4

66.2 77.5 41.6 23.6

34.6 24.8 34.5 42.8

Urine Hyp CTx NTx

4.8 6.3 6.3

18.5 24.4 15.8

45.7 59.3 51.2

52.9 69.8 47.1

Patients and Methods Patients and Controls Thirty-eight patients with Paget’s disease, 18 men and 20 women, aged 36 – 86 years (mean ⫾ SEM: 63.6 ⫾ 2.07 years), were studied. In all patients, diagnosis of Paget’s disease was documented by radiography and bone scintigraphy. Liver and kidney function tests were normal in all cases. Patients who had been treated with calcitonin during the previous year, or during the previous 2 years with plycamycin, tiludronate, or any other bisphosphonate, were not included in the study. Also, patients with skull involvement were excluded because it has been shown that this location is associated with differing behavior of biochemical markers.2 All patients began treatment with tiludronate. The indications for treatment were: (i) symptomatic disease; (ii) serum tAP above the upper limit of the normal range; and (iii) locations where progression of the disease could lead to future complications (despite normal values for tAP). Paget’s disease was considered monostotic when the disease affected only a single bone, and polyostotic when two or more bones were involved. All patients provided informed consent for participation, and the ethics committee of the hospital approved the study. Reference values were obtained from a sample of 55 healthy subjects of similar age and gender, with no evidence of any disturbance of calcium metabolism or metabolic bone disease. Study Design This investigation was a prospective open-label, oral dose study. All patients received 400 mg/day of oral tiludronate for 3 months. Patients were carefully instructed to take the tiludronate 2 h after breakfast with 200 mL of water, as food may interfere with intestinal absorption, and not to take dairy products or antacids containing calcium, iron, magnesium, or aluminum within 2 h of treatment. Laboratory assessment was carried out on each patient before the start of treatment and 1 and 6 months after discontinuation of therapy. Bone scintigraphy was performed at baseline and at 6 months after the end of the treatment.

Interassay analytical coefficients of variation were obtained from control values in the pathological range. Data for biological variation (withinand between-subject variations) and values for critical differences were obtained from patients with stable Paget’s disease. KEY: bAP, bone alkaline phosphatase; CTx, C-terminal telopeptide of type I collagen; Hyp, hydroxyproline; NTx, N-terminal telopeptide of type I collagen; PINP, procollagen type I N-terminal propeptide; sCTx, serum CTx; tAP, total alkaline phosphatase.

Biochemical Determinations Blood and 2 h fasting urine samples were obtained on the same day between 8:00 and 10:00 A.M. Serum and centrifuged urine samples were kept frozen at ⫺20°C until analysis. Serum tAP activity was measured by a spectrophotometric kinetic assay, according to the recommendations of the Scandinavian Committee for Clinical Chemistry and Clinical Physiology, using a DAX 72 analyzer (Bayer Diagnostics Technicon, Tarrytown, NY). Serum bAP was assayed using a immunoradiometric method (Hybritech, Liege, Belgium). Serum PINP determinations were made by a radiometric method using a kit from Orion (Espoo, Finland). Serum CTx and urinary CTx and NTx were assayed by enzyme immunoassays (Cis-Bio International, Gif-sur-Yvette, France and Ostex, Seattle, WA). Urinary Hyp was measured by high-performance liquid chromatography. Urine determinations were expressed in relation to creatinine excretion. Measurement of urinary creatinine was performed with a Cobas Mira S analyzer using an assay based on a modified Jaffe method (kit from Roche Diagnostics, Basel, Switzerland). Assessment Criteria

Quantitative Bone Scintigraphy Bone scintigraphy was performed 2 h after an intravenous injection of 740 MBq (20 mCi) of 99m-technetium-hydroxymethylene diphosphonate. Whole-body images were acquired simultaneously in both the anterior and posterior views using a dual-headed gamma camera (Helix, Elscint, Israel) and stored in a 512 ⫻ 512 matrix for quantitative analysis. Radiotracer uptake for each affected bone was estimated as the geometric mean measured from the anterior and posterior scintigraphic views. Moreover, a reference value was obtained as the ratio between the uptake for an unaffected bone (usually the femur) and the area of this bone. Finally, a scintigraphic activity index (SAI), which reflects both the extent and activity of the disease, was obtained by dividing the sum of radiotracer uptake for all the affected bones by the reference value.16

The interassay analytical coefficients of variation, within- and between-subject variations (expressed as coefficient of variation), and values for critical differences (as percentages) for each marker are shown in Table 1. According to the model of Fraser and Harris, the analysis of variance (ANOVA) test was used to estimate the betweensubject biological variation and values for critical differences. Both parameters for each biochemical marker were obtained from a group of 15 patients with stable Paget’s disease.3 The between-subject variation (S2g) was obtained by subtracting the within-subject plus analytical variation (Si2 ⫹ a) from the total variation (S2total)8: 2 2 共S g2兲 ⫽ 共S total 兲 ⫺ 共S i⫹a 兲

Critical differences (also referred to as least significant change and reference change values) were obtained according to8:

⫺59 ⫺26 ⫺40 290 ⫾ 40b,e 5389 ⫾ 558a,f 7532 ⫾ 1394f ⫺44 ⫺23

冑 2 * 冑 (CV2i ⫹ CVa2)

Statistical Analysis Results were analyzed by nonparametric tests, because the distributions of biochemical markers were skewed. Between-group comparisons were performed using the Mann–Whitney U-test, and the Spearman’s rank correlation test was used for correlation studies. Differences between proportions were assessed by chisquare test. All statistical calculations were made using the STATGRAPHICS statistical software package (STSC, Inc., Rockville, MD). Results Percentage variation data expressed in relation to baseline values. KEY: BCE, bone collagen equivalents; Cr, creatinine. See Table 1 for other definitions. a p ⬍ 0.0001, bp ⬍ 0.05 differences vs. control values. c p ⬍ 0.0001, dp ⬍ 0.001, ep ⬍ 0.05 differences vs. baseline values. f p ⬍ 0.05 differences between monostotic and polyostotic patients.

⫺34 ⫺23 ⫺48 224 ⫾ 17d 3707 ⫾ 263a 3178 ⫾ 993 ⫺49 ⫺29 184 ⫾ 24d 3458 ⫾ 346b,e 468 ⫾ 93b 5057 ⫾ 508a 5381 ⫾ 1156 186 ⫾ 24.7 2264 ⫾ 242

393 ⫾ 40 45 ⫾ 5a 137 ⫾ 18a 179 ⫾ 13a 172 ⫾ 22a 146 ⫾ 6.8 12.7 ⫾ 0.9 35 ⫾ 3.6 75 ⫾ 5.1 33 ⫾ 4.6

tAP (U/L) bAP (ng/mL) PINP (ng/mL) Hyp (nmol/L 䡠 mg Cr) NTx (nmol/L 䡠 BCE per mmol/L Cr) CTx (␮g 䡠 mmol/L Cr) sCTx (pmol/L) SAI

449

where CVi and CVa are the coefficients of variation of withinsubject biological variation and interassay analytical variation, respectively. Size of treatment response was calculated as the difference between the value at 1 and 6 months after therapy and the baseline value for each marker, and expressed as a percentage. To assess the best markers for monitoring response, a ratio between the size of treatment response and variability for each marker was calculated.6 Thus, the best markers would be those with the greatest percentage changes between baseline and follow-up values and the lowest values of critical difference. In this sense, a ratio of ⬎1 indicates a significant decrease of the bone marker after treatment and a ratio of ⬍1 indicates a nonsignificant response to treatment. Thus, the higher the ratio, the more useful the marker. To evaluate the evolution of bone markers based on disease activity, patients were classified as polyostotic or monostotic, because polyostotic patients have previously shown significantly higher bone scan indices of disease activity compared with monostotic patients.2

472 ⫾ 101a,f 5980 ⫾ 803a,f

⫺57 ⫺72 ⫺72 ⫺50 ⫺66 966 ⫾ 208 135 ⫾ 33a,f 345 ⫾ 82a,f 282 ⫾ 33a,f 387 ⫾ 74a,f ⫺41 ⫺62 ⫺57 ⫺47 ⫺52 200 ⫾ 12 15 ⫾ 1.3c 51 ⫾ 7.9d 89 ⫾ 6c 70 ⫾ 10.7b,d 175 ⫾ 13 14 ⫾ 1.1c 40 ⫾ 6.2c 94 ⫾ 9d 52 ⫾ 7.6b,c

⫺52 ⫺65 ⫺68 ⫺44 ⫺65

a,d

% % 1 month

c a

Baseline Controls Marker

Critical difference ⫽ 1.96 *

791 ⫾ 143a,f 7884 ⫾ 1024d,f 14,295 ⫾ 3703f

⫺60 ⫺76 ⫺73 ⫺50 ⫺66 274 ⫾ 33 25 ⫾ 4.9a,e 73 ⫾ 13a,c 121 ⫾ 12a,d,f 98 ⫾ 12a,d

%

310 ⫾ 38 31 ⫾ 5.3a,e,f 104 ⫾ 28a,e,f 151 ⫾ 19a,e,f 139 ⫾ 37a,e,f

a,e

6 months %

a,e,f

1 month

L. Alvarez et al. Treatment response in Paget’s disease

6 months

Baseline

a,f

Polyostotic Monostotic

Table 2. Biochemical markers of bone turnover and scintigraphic activity index (SAI) in patients with monostotic and polyostotic Paget’s disease at baseline and after 1 and 6 months from the end of treatment (data expressed as mean ⫾ SEM)

Bone Vol. 29, No. 5 November 2001:447– 452

At Entry Seven patients withdrew from treatment during the first month. Ultimately, 31 patients were evaluated, including 17 patients (7 men and 10 women) with monostotic disease and 14 (9 men and 5 women) with polyostotic disease. All patients (monostotic and polyostotic) showed higher mean baseline values for all markers compared with controls. As expected, patients with polyostotic disease showed higher mean values for all bone markers than monostotic patients (Table 2). The scintigraphic activity index ranged from 545 to 40,966 (mean ⫾ SEM; 9201.1 ⫾ 1671.6), with significantly lower values in monostotic than in polyostotic patients (5381 ⫾ 1156 vs. 14,295 ⫾ 3073, p ⬍ 0.001). Follow-up Whole group. Among markers of bone formation, serum PINP and bAP showed the most marked decrease after treatment, with reductions of ⬎60%, at both timepoints (Figure 1). The percentage reduction of both markers differed significantly from that of tAP (p ⫽ 0.001). Among markers of bone resorption, urinary NTx showed the highest response after therapy, with a reduction of 68% (Figure 1). This percentage reduction was significantly different from that of the other resorption markers. The scintigraphic activity index decreased by 44% at 6 months after the end of the treatment (9201 ⫾ 1671 vs. 5044 ⫾ 908, p ⬍ 0.05). None of the patients showed disappearance of uptake on skeletal scintigraphy.

450

L. Alvarez et al. Treatment response in Paget’s disease

Bone Vol. 29, No. 5 November 2001:447– 452

Ratios for Monitoring Changes in Follow-up Serum bAP and PINP were the markers with the highest ratios throughout the study, in both polyostotic and monostotic patients (Figure 2). Among markers of bone resorption, urinary NTx was the marker that presented the highest ratios. Conversely, urinary and serum CTx were the markers with the lowest ratios throughout the study (Figure 2). Furthermore, serum bAP and PINP showed ratios of ⬎2, reflecting both a significant treatment response and low variability, whereas Hyp, CTx, and sCTx showed ratios of ⬍1, suggesting higher variability than the size of the treatment response. Individually, at 1 month after the end of treatment, a ratio of ⬎1 was obtained in 96% of patients for PINP and bAP and in 81% of patients for tAP. The remaining 19% of patients with tAP ratios of ⬍1 had mild disease activity (serum tAP 301 ⫾ 15.46 U/L). Among resorption markers, 85% of patients had ratios of ⬎1 for NTx, 40% of patients for Hyp, and ⬍16% for CTx and sCTx. There was a trend toward higher ratios for monitoring response in polyostotic patients at 6 months, whereas, in monostotic patients, the highest ratios were observed at 1 month (Figure 2). In this patients group, only PINP showed an index ratio of ⬎1 (mean ratio 1.139) between 1 and 6 months after therapy. Correlation Between Bone Markers and Quantitative Bone Scan Indices At entry, all markers correlated significantly with scintigraphic index, whereas, at 6 months, only collagen-related markers were correlated significantly. PINP and NTx were the markers with the highest correlation coefficients, at entry and at 6 months after the end of treatment (Table 3). There was no correlation, however, between the percentage change of scintigraphic indices and percentage change of biochemical markers throughout the study. Figure 1. Mean percentage (⫾ SEM) of variation of biochemical markers of bone turnover in relation to baseline values in patients with Paget’s disease at 1 and 6 months from the end of treatment with tiludronate (#significant difference compared with other markers of the group).

Monostotic and Polyostotic Patients. The mean values as well as the percentage reduction in bone markers and scintigraphic indices throughout the study for monostotic and polyostotic patients are shown in Table 2. At 1 and 6 months after the end of treatment, the mean values for all bone formation markers decreased significantly in both groups of patients. Nevertheless, differences vs. the control group still persisted in polyostotic patients, whereas monostotic patients differed only in serum tAP (Table 2). Except for sCTx, all resorption markers decreased significantly after treatment in monostotic as well as in polyostotic patients. sCTx showed a significant diminution in monostotic patients only at 1 month (Table 2). Patients with polyostotic disease showed a continuous decrease in mean levels of all bone markers for up to 6 months after the end of the treatment, whereas, in monostotic patients, there was a trend toward increased levels at this time (Table 2). In this of patients group, serum PINP was the only marker showing significant differences in mean values at 6 months when compared with the 1 month values (51.79 ⫾ 7.9 vs. 40 ⫾ 6.2 ng/mL, p ⬍ 0.018). The scintigraphic activity index decreased in both monostotic and polyostotic patients, although there were no significant differences from baseline values (Table 2).

Discussion This study has shown that serum bAP, and to a lesser extent PINP, are the most sensitive markers for monitoring bisphosphonate treatment in Paget’s disease. Thus, both markers showed the highest percentage reduction as well as the highest ratios for monitoring treatment response throughout the study. Among resorption markers, urinary NTx showed the greatest reduction and the best ratios for monitoring. It has recently been reported that determination of serum bAP and PINP, as markers of bone formation, and urinary NTx, as a marker of bone resorption, provide the best biochemical approach to ascertain the extent and activity of Paget’s disease.2 The present study provides additional information by showing that these markers are also the most sensitive for monitoring treatment efficacy. Until now, most studies have assessed biochemical response or remission after therapy with measurements of serum tAP and occasionally urinary Hyp.12,19 Furthermore, therapeutic strategies have been based on changes in serum tAP levels after a course of therapy.21 Thus, although important advances in Paget’s disease treatment have been achieved in recent years, the conventional parameters for measuring bone turnover are still used, irrespective of disease activity and extension. In isolated studies, when more sensitive markers such as serum bAP and urinary NTx have been included in the evaluation of bisphosphonate therapy, greater reductions in their levels have been described when compared with classical markers.4,14,15,17,18 The assessment of biological variability of bone markers in Paget’s disease makes it possible to evaluate the magnitude of the fluctuations that will reflect a true change in the disease

Bone Vol. 29, No. 5 November 2001:447– 452

L. Alvarez et al. Treatment response in Paget’s disease

451

Figure 2. Ratios for monitoring response for each marker at 1 and 6 months from the end of treatment with tiludronate in monostotic and polyostotic patients.

activity. These data allow proper assessment and comparison of the usefulness of bone markers in monitoring therapy. Previous studies have shown a higher variability for urinary markers, and thus it was suggested that serum markers would be better for monitoring purposes. We confirm this by means of evaluating their biochemical response after treatment and demonstrating that they have the highest ratio values for monitoring changes, indicating the usefulness of serum bAP and PINP in the follow-up of pagetic patients after therapy. It should be pointed out, however, that serum tAP also showed both high percentages

of response and high ratios for monitoring changes, indicating its utility in the follow-up of treatment for Paget’s disease, especially in patients with high disease activity. Thus, nearly 20% of patients showed monitoring ratios of ⬍1 after therapy, and all these patients had mild Paget’s disease. These data are of interest, both in terms of cost-benefit, because the determination of serum tAP is inexpensive, and in practicability, because the test is easy to perform. Among resorption markers, urinary NTx showed high sensitivity in evaluating responses and monitoring therapy. Previous

Table 3. Correlation between biochemical markers of bone turnover and scintigraphic activity index (SAI) at baseline and at 6 months from the end of therapy tAP

bAP

PINP

Hyp

NTx

CTx

sCTx

SAI Baseline

0.686 (0.0004)

0.772 (0.0001)

0.886 (0.0001)

0.705 (0.0003)

0.863 (0.0001)

0.589 (0.0027)

0.5838 (0.0042)

SAI 6 months

0.236 (0.22)

0.37 (0.0643)

0.716 (0.0005)

0.4734 (0.013)

0.6525 (0.0009)

0.563 (0.0041)

0.6386 (0.0018)

Spearman rank correlation coefficients. Significance level values in parentheses. See Table 1 for definitions.

452

L. Alvarez et al. Treatment response in Paget’s disease

studies have supported the high sensitivity of NTx, with percentage reductions of around 80% during the first few months of therapy.4,14,18 These data suggest the usefulness of this marker preferentially at an early stage of antiresorptive therapy, and in patients with a purely osteolytic lesion. Conversely, serum and urinary CTx showed low percentages of response and also the lowest monitoring ratios. Previous studies have indicated an alteration of the degree of ␤-isomerization of collagen type I in Paget’s disease that can be modified with treatment of the disease.9,10 Because urinary and serum CTx measured the ␤-isomerized fragments of the carboxyterminal telopeptides of collagen I,5,9 a progressive replacement of woven bone by lamellar bone with higher degree of ␤-isomerization after treatment cannot be ruled out. Biochemical markers of bone turnover showed different patterns of response after therapy depending on the extent and activity of the disease. Thus, in polyostotic patients, the tendency of mean values, as well as the percentage decrease of bone markers, was to continue decreasing at 6 months from the end of treatment, whereas, in monostotic patients, markers tended to increase during this time. This might be explained by the mechanism of action of bisphosphonates, as they accumulated in bone with subsequent release from the mineralized matrix. Moreover, it has been suggested that the proportion of bisphosphonates retained by bone is related to the skeletal turnover.1,11 Thus, in patients with Paget’s disease, the activity and extension of bone lesions may influence long-term response to bisphosphonates at least 6 months after treatment. Although in nearly 50% of the patients bone markers decreased to normal values after therapy, in none of them did pagetic lesions disappear according to bone scan. This observation suggests that a cure for this disease cannot be achieved with our therapeutic regimen. These data are consistent with the trend toward increases in bone markers at 6 months from the end of therapy in monostotic patients. The differing response of markers to bisphosphonate therapy, depending on the activity of the disease, can be helpful in understanding the mechanism of action of these drugs and for selecting optimal doses. We conclude that the use of serum bAP and PINP may help the clinician to formulate therapeutic strategies for pagetic patients. Serum tAP, however, may also be a useful marker in monitoring treatment, especially in more active disease. We also conclude that the use of critical difference values of bone markers is mandatory for assessing true changes induced by treatment, and thus they may be considered as real threshold values in clinical practice. Taking into account both observations, the new markers improve follow-up assessment in patients being treated, a relevant finding as new and powerful medications become available.

Acknowledgments: The authors are grateful to Montserrat Portas for her technical assistance and to Andy Hawker for reviewing the English.

Bone Vol. 29, No. 5 November 2001:447– 452

3.

4.

5.

6. 7. 8. 9.

10.

11. 12.

13. 14.

15.

16.

17.

18.

19.

20.

21.

References 1. Adami, S. and Zamberlan, N. Adverse effects of bisphosphonates. A comparative review. Drug Safety 14:158 –170; 1996. 2. Alvarez, L., Peris, P., Pons, F., Guan˜ abens, N., Herranz, R., Monegal, A., Bedini, J. L., Deulofeu, R., Martinez de Osaba, M. J., Mun˜ oz-Go´ mez, J., and Ballesta, A. M. Relationship between biochemical markers of bone turnover

and bone scintigraphic indices in assessment of Paget’s disease activity. Arthritis Rheum 40:461– 468; 1997. Alvarez, L., Rico´ s, C., Peris, P., Guan˜ abens, N., Monegal, A., Pons, F., and Ballesta, A. M. Components of biological variation of biochemical markers of bone turnover in Paget’s disease of bone. Bone 26:571–576; 2000. Blumsohn, A., Naylor, K. E., Assiri, A. M. A., and Eastell, R. Different responses of biochemical markers of bone resorption to bisphosphonate therapy in Paget disease. Clin Chem 41:1592–1598; 1995. Bonde, M., Garnero, P., Fledelius, C., Qvist, P., Delmas, P. D., and Christiansen, C. Measurement of bone degradation products in serum using antibodies reactive with an isomerized form of an 8 amino acid sequence of the C-telopeptide of type 1 collagen. J Bone Miner Res 12:1028 –1034; 1997. Braga de Castro Machado, A., Hannon, R., and Eastell, R. Monitoring alendronate therapy for osteoporosis. J Bone Miner Res 14:602– 607; 1999. Delmas, P. D. and Meunier, P. J. The management of Paget’s disease of bone. N Engl J Med 336:558 –566; 1997. Fraser, C. G. and Harris, E. K. Generation and application of data on biological variation in clinical chemistry. Crit Rev Clin Lab Sci 27:409 – 437; 1989. Garnero, P., Fledelius, C., Gineyts, E., Serre, C., Vignot, E., and Delmas, P. D. Decreased ␤-isomerization of the C-terminal telopeptide of type I collagen ␣1 chain in Paget’s disease of bone. J Bone Miner Res 12:1407–1415; 1997. Garnero, P., Gineyts, E., Schaffer, A. V., Seaman, J., and Delmas, P. D. Measurement of urinary excretion of non-isomerized and ␤-isomerized forms of type I collagen breakdown products to monitor the effects of the bisphosphonate zoledronate in Paget’s disease. Arthritis Rheum 41:354 –360; 1998. Kanis, J. A., Gertz, B. J., Singer, F., and Ortolani, S. Rationale for the use of alendronate in osteoporosis. Osteopor Int 5:1–13; 1995. Khan, S. A., McCloskey, E. V., Eyres, K. S., Nakatsuka, K., Sirtori, P., Orgee, J., Coombes, G., and Kanis, J. A. Comparison of three intravenous regimens of clodronate in Paget disease of bone. J Bone Miner Res 11:178 –182; 1996. Meunier, P. J. Paget’s disease: Treatment results and expectations with present therapies. J Bone Miner Res 14(Suppl. 2):70 –73; 1999. Papapoulos, S. E. and Fro¨ lich, M. Prediction of the outcome of treatment of Paget’s disease of bone with bisphosphonates from short-term changes in the rate of bone resorption. J Clin Endocrinol Metab 81:3993–3997; 1996. Pedrazzoni, M., Alfano, F. S., Gatti, C., Fantuzzi, M., Girasole, G., Campanini, C., Basini, G., and Passeri, M. Acute effects of bisphosphonates on new and traditional markers of bone resorption. Calcif Tissue Int 57:25–29; 1995. Pons, F., Alvarez, L., Peris, P., Guan˜ abens, N., Vidal-Sicart, S., Monegal, A., Pavia, J., Ballesta, A. M., Mun˜ oz-Go´ mez, J., and Herranz, R. Quantitative evaluation of Paget’s disease activity. Nucl Med Commun 20:525–528; 1999. Randall, A. G., Kent, G. N., Garcia-Webb, P., Bhagat, C. I., Pearce, D. J., Gutteridge, D. H., Prince, R. L., Stewart, G., Stuckey, B., Will, R. K., Retallack, R. W., Price, I. R., and Ward, L. Comparison of biochemical markers of bone turnover in Paget disease with Pamidronate and a proposed model for the relationships between measurements of the different forms of pyridinoline cross-links. J Bone Miner Res 11:1176 –1184; 1996. Reid, I. R., Nicholson, G. C., Weinstein, R. S., Hosking, D. J., Cundy, T., Kotowicz, M. A., Murphy, W. A., Yeap, S., Dufresne, S., Lombardi, A., Musliner, T. A., Thompson, D. E., and Yates, J. Biochemical and radiologic improvement in Paget’s disease of bone treated with alendronate: A randomized, placebo-controlled trial. Am J Med 101:341–348; 1996. Roux, C., Gennari, C., Farrerons, J., Devogelaer, J. P., Mulder, H., Kruse, H. P., Picot, C., Titeux, L., Reginster, J. Y., and Dougados, M. Comparative prospective, double-blind, multicenter study of the efficacy of tiludronate and etidronate in the treatment of Paget’s disease of bone. Arthritis Rheum 38:851– 858; 1995. Siris, E. S. Paget’s disease of bone. In: Favus M. J. Ed. Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 4th Ed. Philadelphia: Lippincott Williams & Wilkins, 1999; 415– 425. Siris, E. S. Goals of treatment for Paget’s disease of bone. J Bone Miner Res 14(Suppl. 2):49 –52; 1999.

Date Received: July 11, 2000 Date Revised: May 10, 2001 Date Accepted: May 10, 2001