Renal Excretion of ""Tc-Diphosphonate in Osteomalacia J. D. MACFARLANE, B.M.; M. R. A. KHAIRI, M.D.; M. RICCIARDONE, B.S.; H. N. WELLMAN, M.D.; and C. C. JOHNSTON, Jr., M.D. Indiana University School of Medicine; Indianapolis, Indiana INTEREST IN BONE SCANNING in metabolic bone disease has led to the identification of pseudofractures in osteomalacia (1), the assessment of the severity of renal osteodystrophy (2), and the suggestion that calculation of bone to soft-tissue ratios may help distinguish patients with bone disease from normal control persons (3). These techniques are relatively crude and do not necessarily indicate the real skeletal accretion or whole body retention of the radionuclide. During a study of sequential bone to soft-tissue ratios in patients with various bone diseases, we estimated the renal excretion of 99mTc-ethane-1 -hydroxy- 1, 1-diphosphonate (99mTc-EHDP). We report here our findings from a study of the renal excretion of 99mTc350

March 1979 • Annals of Internal Medicine • Volume 90 • Number 3

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E H D P in a patient with osteomalacia and compare her results with those obtained in four patients with idiopathic osteoporosis. A 51-year-old white woman was first seen at this center in December 1976. She had been extensively evaluated elsewhere because of a malabsorption syndrome dating back to 1965. Major features included intestinal lactase deficiency, protein-losing enteropathy, and fat malabsorption. In addition, she had a monoclonal gammopathy, uveitis, clubbing, and osteopenia. She had not had intestinal surgery or anticonvulsant or laxative medication. Increasing limb pain and proximal muscle weakness led to hospital admission. Because of her clinical features, deficient diet, and pelvic pseudofracture, osteomalacia was suspected and confirmed by bone biopsy. A bone scan was done using 21.9 mCi of Osteoscan® (99mTc-EHDP) (Procter and Gamble, Cincinnati, Ohio) and sequential assessment of bone (lumbar spine) to soft-tissue ratios every 2 minutes in the first 30 minutes and thereafter at 30-minute intervals up to 4 h. Qualitative assessment of skeletal appearances was made from multiple views obtained during the 4th h. Starting at the time of ""Tc-EHDP injection, three consecutive 8-h urine collections were obtained, and the percentage of the administered dose excreted was assessed by comparing the radioactivity in urine aliquots with an aliquot from a 10-mCi standard of the agent prepared at the time of original injection. This obviated the need for calculations based on decay. At the level of excretion found, the error is about ± 2%, no doubt less than the error inherent in obtaining three 8-h urine collections. The patient improved after receiving appropriate calcium and vitamin D replacement therapy. She was re-evaluated 13 months later, with her informed consent, and a second bone scan, urine excretion measurement, and a bone biopsy were done. Relevant results from these investigations, both before and after therapy, are included in Table 1. Renal function was normal on both occasions. Qualitative assessment of the initial bone scan revealed a diffusely increased skeletal uptake at 4 h with no focal abnormalities. The kidneys showed an apparently reduced uptake of the nuclide. The second bone scan at 4 h showed no significant changes from the pretreatment scan except that the soft-tissue background uptake was possibly a little greater. The early bone soft-tissue ratios were not strikingly different. The ratios at 4 h are included in Table 1, as are details of the urinary radionuclide, excretions. Four patients with idiopathic osteoporosis, and no biochemical or histologic evidence of osteomalacia, underwent an identical urinary excretion assessment and bone scan with 9 9 m Tc-EHDP. The 24-h radionuclide excretions in these patients ranged from 65.7% to 85.2% of the administered dose (mean, 77.5%). The reproducibility of urinary excretions estimation was tested in one of these patients, and results agreed within 3.5%. The major part of the renal excretion of 9 9 m Tc-EHDP occurs in the first few hours. The percentage of administered radioactivity appearing in the urine in 24 h in six normal subjects given a 1-mCi dose was 79.2 ± 7.24% (4). The mean 24-h excretion (77.5%) in* our four osteoporotic patients was similar, as was the excretion, after replacement therapy, in the patient with osteomalacia. Before therapy, however, the amount excreted was much less (32.16%), and this finding suggests that the osteomalacic skeleton was avid for the radionuclide. This observation is supported both by the qualitative appearances of the bone scans and by the change in the lumbar spine to soft-tissue ratio after therapy. This phenomenon is also supported by other studies that show a special affinity of technetium polyphosphate compounds for immature col-

Table 1 . Laboratory Investigations, Bone Biopsy Data, and Urinary Radionuclide Excretion Results

Feature

Normal Range

Blood urea nitrogen, mg/dl 10-20 Creatinine, mg/dl

Renal excretion of 99mTc-diphosphonate in osteomalacia.

Renal Excretion of ""Tc-Diphosphonate in Osteomalacia J. D. MACFARLANE, B.M.; M. R. A. KHAIRI, M.D.; M. RICCIARDONE, B.S.; H. N. WELLMAN, M.D.; and C...
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