Changes in biochemical parameters of bone turnover and bone mineral density in post-pregnancy osteoporosis

Changes in biochemical parameters of bone turnover and bone mineral density in post-pregnancy osteoporosis

Changes in biochemical parameters of bone turnover and bone mineral density in post-pregnancy osteoporosis Shigeichiro Honjo, MD, PhD, and Hideki Mizu...

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Changes in biochemical parameters of bone turnover and bone mineral density in post-pregnancy osteoporosis Shigeichiro Honjo, MD, PhD, and Hideki Mizunuma, MD, PhD Maebashi, Gunma, Japan A lactating 32-year-old woman in whom severe back pain developed 5 months after delivery is described. Cross-linked carboxyterminal telopeptide of type I collagen and pyridinoline, which are parameters of bone resorption, was markedly elevated with low bone mineral density. A high level of bone resorption was associated with post-pregnancy osteoporosis. (Am J Obstet Gynecol 2001;185:246-7.)

Key words: Post-pregnancy osteoporosis, cross-linked carboxyterminal telopeptide of type I collagen, pyridinoline, bone resorption

We managed a case of post-pregnancy osteoporosis with severe back pain for 18 months. To make diagnosis, magnetic resonance imaging and a bone biopsy were performed. Parameters of bone turnover and bone mineral density were examined before and during treatment with vitamin D and calcium. Case report A 32-year-old woman came to the hospital in July, 1997, with severe back pain. She had delivered her first infant at term through cesarean delivery 5 months before her visit. This back pain prevented her from sitting, standing, and walking. She had not experienced any back pain during her pregnancy. Dual energy x-ray absorptiometry, magnetic resonance imaging, radiographs of the spine, and a bone biopsy of lumbar vertebra (L3) were performed intensively to determine the cause of the pain. Calcitonin, intact-parathyroid hormone, biochemical parameters of bone formation and bone resorption such as bone Gla protein, carboxyterminal propeptide of type I procollagen, bone type alkaline phosphatase, pyridinoline, deoxypyridinoline, and cross-linked carboxyterminal telopeptide of type 1 collagen were measured for assessing the level of bone turnover. Dual energy x-ray absorptiometry showed a bone mineral density of her L2 to L4 spine of 0.687 g/cm2 (–4.06 standard deviation score from control subjects of the same age). Radiographs of the spine did not show any marked deformities; however, magnetic resonance imaging showed diffuse and patchy hypointense lesions in the bone mar-

From the Department of Obstetrics and Gynecology, Gunma University School of Medicine. Received for publication September 14, 2000; accepted December 30, 2000. Reprint requests: Shigeichiro Honjo, MD, PhD, Department of Obstetrics and Gynecology, Gunma University School of Medicine, 472-6 KamiShinden-machi, Maebashi, Gunma, 371-0821, Japan. Copyright © 2001 by Mosby, Inc. 0002-9378/2001 $35.00 + 0 6/1/113910 doi:10.1067/mob.2001.113910

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Table. Changes in levels of biochemical parameters and BMD during treatment Time since treatment (mo) Baseline

6

12

18

Parameters for bone formation BGP (ng/mL) 4.1 2.0 4.4 4.1 B-ALP (U/L) 94 92 45 24 P1CP (ng/mL) 146.5 66.8 70.4 67.5 Parameters for bone resorption Pyr (nmol/mmol Cr) 50.1* 32.1* 27.2 18.7 D-Pyr (nmol/mmol Cr) 6.3 5.1 3.5 4.5 1CTP (ng/mL) 6.5* 4.2 4.0 3.3 BMD (g/cm2) 0.687 0.707 0.729 0.769 BGP, Bone Gla protein; B-ALP, bone type alkaline phosphatase; P1CP, carboxyterminal propeptide of type I procollagen; Pyr, pyridinoline; Cr, creatinine; D-Pyr, deoxypyridinoline; 1CTP, cross-linked carboxyterminal telopeptide of type 1 collagen; BMD, bone mineral density. *Higher than normal limits.

row of the lumbar spine. A bone biopsy specimen showed trabecular thinning and loss of trabeculae. Baseline levels of calcitonin and intact-parathyroid hormone were normal: 20 pg/mL and 37 pg/mL, respectively. Baseline levels of cross-linked carboxyterminal telopeptide of type I collagen and pyridinoline were higher than normal limits. Baseline levels of the other parameters were normal (Table). Treatment was initiated with vitamin D (1 α OHD3) and calcium soon after examination. On follow-up, the back pain had markedly diminished 12 months after treatment. Bone mineral density of L2 to L4 increased rapidly from 0.687 g/cm2 to 0.769 g/cm2 (–3.17 standard deviation score from controls of the same age) 18 months after treatment, and the levels of all biochemical parameters except bone Gla protein showed time- dependent decreases. Comment We found that the baseline levels of cross-linked carboxyterminal telopeptide of type I collagen and pyridino-

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line, the parameters of bone resorption, were markedly elevated while those of bone formation were within normal limits in our patient with post-pregnancy osteoporosis. It indicated that the high level of bone resorption occurred, which was most likely responsible for the extremely low bone mineral density and severe back pain. Post-pregnancy osteoporosis is a rare but potentially serious condition leading to back or hip pain and fractures. A previous study1 showed the changes in levels of calcium regulatory hormones or parameters of bone turnover in lactating women. However, the pathogenesis and biochemical features of post-pregnancy osteoporosis have not been clearly elucidated. Magnetic resonance imaging was performed because of a concern about severe back pain, even though no remarkable deformities could be detected in the radiographs of the spine. Magnetic resonance imaging is a precise and useful procedure in mak-

ing diagnosis when radiographs do not show any remarkable findings, as in our patient.2 On the other hand, a bone biopsy was performed to confirm the diagnosis and to exclude a metastasis of malignant tumor or other metabolic diseases. This case represents clearly the elevated bone resorption as a likely pathogenesis of post-pregnancy osteoporosis, and the usefulness of cross-linked carboxyterminal telopeptide of type I collagen and pyridinoline as diagnostic markers in post-pregnancy osteoporosis. REFERENCES

1. Cross NA, Hillman LS, Allen SH, Krause GF. Changes in bone mineral density and markers of bone remodeling during lactation and postweaning in women consuming high amounts of calcium. J Bone Miner Res 1995;10:1312-20. 2. Smith R, Athanasou NA, Ostlere SJ, Vipond S. Pregnancy-associated osteoporosis. QJM 1995;88:865-78.