Bone Marrow Immuno-scintigraphy (BMIS): A New and Important Tool for the Assessment of Marrow Fibrosis in Renal Osteodystrophy?

Chan-Duck Kim, Sung-Ho Kim, Yong-Lim Kim, Dong-Kyu Cho, Jae-Tae Lee1

One of the classic histologic forms of renal osteodystrophy is osteitis fibrosa, and its distinguishing characteristic is bone marrow (BM) fibrosis, caused by the activation of marrow parenchymal cells. A bone biopsy must be performed in order to establish the diagnosis of renal osteodystrophy. The clinical use of bone biopsy is restricted, however, due to the invasiveness of the procedure. In recent studies, bone scans have provided information useful for the differential diagnosis between osteomalacia and osteitis fibrosa. However, bone scans can not provide information on the bone marrow status. Bone marrow immunoscintigraphy (BMIS) using Tc-99m antigranulocyte antibody (AGA), a highly sensitive test for the detection of bone marrow abnormalities which is also a noninvasive method, has rarely been reported in chronic renal failure (CRF). BMIS can provide information in patients with myelofibrosis. The purpose of this study was to evaluate the usefulness of BMIS in CRF patients with special regards to biochemical parameters.

Nineteen CRF patients (13 men, 6 women; mean age: 48 ± 11 years) in whom bone scintigraphy using Tc-99m MDP (methylene diphosphonate) showed the so-called superscan pattern were included in the study. Their primary renal diseases were chronic glomerulonephritis (n = 14), diabetes (n = 4), and polycystic kidney disease (n = 1). Modes of therapies were continuous ambulatory peritoneal dialysis (CAPD) (n = 13; mean duration: 9.5 months), HD (n = 5; mean duration: 7.8 months), and conservative treatment (n = 1). BMIS using Tc-99m labeled anti-granulocyte monoclonal mouse antibody BW250/183 was performed, and the results were compared with the biochemical parameters of the patients.

According to the presence of BM expansion, which may represent marrow fibrosis, the 19 patients were divided into two groups: Group I (n = 7) with BM expansion and Group II (n = 12) with normal marrow distribution. The biochemical parameters and bone markers of Group I were compared with those of Group II. There was no significant difference in biochemical parameters (blood hemoglobin, serum ferritin, erythropoietin, BUN, creatinine) between the two groups. There were no significants difference in serum calcium, phosphorus, tartate-resistant acid phosphatase (TRAP), and intact parathyroid hormone (iPTH) between the two groups. Serum alkaline phosphatase (ALP) and osteocalcin were significantly (P < 0.05) higher in Group I than in Group II.

These results suggest that patients with bone marrow expansion in BMIS have increased levels of ALP and osteocalcin, indicating an increased osteoblastic activity. BMIS may be useful for the detection of bone marrow expansion due to marrow fibrosis in renal osteodystrophy, and for the evaluation of the extent of bone marrow fibrosis.

Key words

Bone marrow immunoscintigraphy (BMIS), renal osteodystrophy, chronic renal failure, hemodialysis

From:

Division of Nephrology, Department of Internal Medicine and 1Department of Nuclear Medicine, Kyungpook University Hospital, Taegu, Korea.

Introduction

Figure 1: Superscan shown in bone scan using Tc-99m MDP (methylene diphosphonate) in chronic renal failure (CRF) patients (a). Markedly expanded bone marrow (b), and normal pattern of marrow (c) in bone marrow immunoscintigraphy using Tc-99m labeled anti-granulocyte antibody.

Renal osteodystrophy, the term used to describe the skeletal complications of end-stage renal disease, is a multifactorial disorder of bone remodeling. Renal osteodystrophy is classified as osteitis fibrosa, osteomalacia, or mixed, mild, or adynamic disease, according to histologic features. The recognition that renal osteodystrophy encompasses a spectrum of disorders may increase the importance of performing a bone biopsy in order to make an accurate diagnosis. However, the clinical use of a bone biopsy is restricted. In recent studies, the Tc-99m methylene diphosphonate (MDP) bone scan has provided useful information for the diagnosis of renal osteodystrophy, and for the differential diagnosis between dialysis-related osteomalacia and secondary hyperparathyroidism (1). In general, tracer uptake is decreased in patients with pure osteomalacia and increased in patients with pure osteitis fibrosa. This latter abnormal pattern is known as a superscan (Figure 1a).

Osteitis fibrosa, a frequent complication of chronic renal failure, is characterized by increased rates of bone formation and bone resorption due to increased secretion of parathyroid hormone (PTH) (2). A hallmark of osteitis fibrosa is marrow fibrosis, caused by the activation of marrow mesenchymal cells, which differentiate into fibroblast-like cells secreting the fibrous tissue into peritrabecular spaces (3). However, a bone scan can not provide information about bone marrow status. Bone marrow immunoscintigraphy (BMIS) using Tc-99m labeled antigranulocyte antibody is a new, highly sensitive test for detection of bone marrow abnormalities, and a noninvasive procedure. There are few reports of its use in chronic renal failure (4,5). The purpose of this study was to evaluate the usefulness of BMIS in renal osteodystrophy patients with special regard to biochemical parameters and bone markers.

Materials and methods

Patients

We studied 19 chronic renal failure (CRF) patients (13 men, 6 women; mean age 48 ± 11 years) with the superscan bone scan technique. Their primary renal diseases were chronic glomerulonephritis (n = 14), diabetic nephropathy (n = 4), and polycystic kidney disease (n = 1). Modes of therapies were peritoneal dialysis (n = 13; mean duration: 9.5 months), hemodialysis (n = 5; mean duration 7.8 months) and conservative treatment (n = 1).

Study parameters

Blood samples were obtained from all patients. Levels of biochemical parameters, including hemoglobin, blood urea nitrogen (BUN), creatinine, ferritin, and erythropoietin (EPO), were measured. As well, bone markers that include serum intact parathyroid hormone (iPTH), alkaline phosphatase (ALP), osteocalcin, calcium, phosphorus, and tartrate-resistant acid phosphatase (TRAP) were measured. A two-site immunoradiometric assay (normal range: 8 - 76 pg/mL, ELISA-PTH, CIS Biointernational) was used to measure iPTH. Osteocalcin was measured using an immunoradiometric assay (normal range 2.4 to 11.7 ng/mL, Nichols Institute Diagnostics, San Juan Capistrano, CA). All other serum parameters were analyzed using conventional autoanalyzer techniques.

Bone scan

Whole-body bone imaging was performed after intravenous injection of 740 MBq of Tc-99m MDP. Considering the normal uptake of the tracer by bone as zero, the images were scored as follows: 2, absence of tracer uptake by bone, intense background activity due to soft-tissue uptake; 1, decrease in bone uptake in the absence of clear delineation of skeletal structures, with intense soft-tissue back ground; +1, increase in tracer uptake by bone with sharp delineation of the axial skeleton; +2, marked increase in tracer uptake by bone with sharp delineation of the skeleton including upper and lower limbs (1). Tracer uptake by bone was increased in all patients. Thirteen subjects scored +1, and 6 subjects scored +2.

Bone marrow immunoscintigraphy (BMIS)

Bone marrow immunoscintigraphy was performed on all 19 patients. Technetium-99m labeled antigranulocyte monoclonal mouse antibody BW 250/183 (Mab) recognizing the nonspecific cross-reacting antigen 95 (Scintimum Granulozyt® CIS, France) was used after preparation according to the manufacturer's instructions. The radiochemical purity was greater than 95%, and 740 MBq of antibody solution was slowly infused intravenously in each patient. No side effects were observed. Scintigraphy was performed using a dual-head camera for whole-body plain imaging at 6 and 24 hours after injection (6). All scintigraphic studies were reviewed by two experienced nuclear medicine physicians. Abnormal uptake in red bone marrow was defined as uptake greater or less than the range in normal marrow. For scoring peripheral expansion of red bone marrow, the Tc-99m-AGA scintigraphic uptake was divided into 5 grades: grade 0 (normal): uptake seen in 0 to 1/3 of the humeri and femora; grade 1: uptake seen in 1/3 to 1/2 of the humeri and femora; grade 2: uptake seen in 1/2 to 3/4 of the humeri and femora; grade 3: uptake seen in more than 3/4 of the humeri and femora, but not including elbows and knees; grade 4: uptake seen beyond elbows and knees (6,7).

Statistical analysis

All data are presented as mean ± SD. The two-tailed Student's t-test was used for statistical analysis. A P value of < 0.05 was considered significant.

Results

According to the presence of bone marrow expansion, 19 patients were divided into two groups: Group I (n = 7) with bone marrow expansion (Figure 1b) and Group II (n = 12) with normal marrow distribution (Figure 1c). In Group I, three cases each were classed as grades 1 and 2, and one case as grade 3, respectively. The biochemical parameters of Group I were compared with those of Group II. Table I shows the characteristics of patients in both groups. The patients in Group I were 50.2 ± 12.0 years old and in Group II 46.2 ± 11.7 years old. There were no significant differences in sex ratio and age. Diabetic nephropathy was the cause of CRF in 33% of the Group II patients, and in 0% of the Group I patients. Biochemical parameters of the two groups are depicted in Table II. There were no significant differences in hemoglobin, serum ferritin, EPO, BUN, and creatinine between two groups. Biochemical bone markers are shown in Table III. There were no significant differences in serum calcium, phosphorus, TRAP, and iPTH between two groups. However, percentage of serum iPTH levels over 300 pg/mL was 71% (5/7) in Group I, and 50% (6/12) in Group II. Alkaline phosphatase was significantly higher in Group I than in Group II (412.8 ± 227.8 IU/L vs. 247.0 ± 123.3 IU/L, P < 0.05). Osteocalcin was also significantly higher in Group I than in Group II (28.9 ± 12.8 ng/mL vs. 17.2 ± 8.1 ng/mL, P < 0.05).

Discussion

Although nonspecific, BMIS using antigranulocyte antibody offers an advantage over standard bone-marrow colloidal scans since it allows for complete visualization of the whole-body bone-marrow distribution. Because the whole-body distribution of bone marrow, including bone marrow replacement and peripheral red-bone-marrow expansion, is completely visualized, bone-marrow immunoscintigraphy using Tc-99m-labeled antigranulocyte antibody has been used successfully for diagnosis and staging of several neoplastic diseases, selecting bone-marrow biopsy sites, and evaluating the extent of intramedullary and extramedullary lesions (46,8). Bone marrow immunoscintigraphy can provide useful information in patients with diseases such as multiple myeloma, leukemia, myelofibrosis, aplastic anemia, bone infarct, with bone marrow transplants, and with infectious and inflammatory processes of the bone (911). The antigranulocyte monoclonal antibody is distributed in a homogeneous pattern in healthy persons, without expansion beyond the proximal thirds of the long bones of the arms and legs in adults. Bone-marrow expansion in adults is associated with myelofibrosis, myeloid metaplasia, and infectious, inflammatory, or malignant disease of the bone. It can be secondary to central-marrow depletion (5). Increased erythropoiesis can also result in bone marrow expansion as in sickle cell anemia and chronic hemolytic states (12,13).

Myelofibrosis occurs not only as a primary idiopathic process, but also as a secondary process induced by a number of neoplasms (14), toxic exposures, systemic disease including renal osteodystrophy, and exposure of experimental animal models to a variety of agents. Renal osteodystrophy, manifested in part by increased bone fibrosis and sclerosis, has been attributed to complex interactions between two hormones, parathyroid hormone and 1,25(OH)2D3 (2,3). Significant fibrosis has been documented and quantified in bone marrow biopsy specimens of patients with renal osteodystrophy receiving long-term dialysis. Bone marrow biopsy is an accurate diagnostic method for detecting myelofibrosis, but its clinical application is limited due to the invasiveness of the procedure. On the other hand, BMIS, a noninvasive method, is valid for diagnosing secondary myelofibrosis in renal osteodystrophy (15). Bone marrow immunoscintigraphy reveals low uptake in the central marrow but expanded peripheral-marrow uptake in patients with myelofibrosis. In our study, among 19 patients with superscan in a bone scan, 7 patients (37%) presented bone marrow expansion in BMIS which may represent marrow fibrosis.

The pathogenesis of bone-marrow fibrosis in renal osteodystrophy is unknown. Fibroblasts may be stimulated by some factors, such as elevated PTH or chemoattractants originating from osteoclasts and/or osteoblasts. Because primary hyperparathyroidism can also lead to secondary myelofibrosis, uremic toxins or other factors associated with end-stage renal disease seem to play a minor role in the development of bone marrow fibrosis (15). Fibrosis of hyperparathyroidism, rather than representing reparative, inert tissue, consists of osteoblast-like cells, probably precursors of osteoblasts derived by parahormone-stimulated proliferation of ALP-positive stromal cells of bone marrow, and of TRAP-positive mononuclear cells, probably preosteoclasts (16). The present study showed that ALP and osteocalcin levels were increased in the bone marrow expansion group. These results suggest that marrow fibrosis in renal osteodystrophy is associated with increased osteoblastic activity.

The anemia of renal failure is a complex disorder determined by a variety of factors. However, decreased erythropoiesis is an important determinant of the anemia of chronic renal failure. Our results show that there were no significant differences between hemoglobin, ferritin, and EPO levels of the two groups, and there was no evidence of chronic hemolysis or blood loss. It may suggest that bone marrow expansion in BMIS is not associated with anemia of CRF.

In patients with uremia, the dose of erythropoietin needed to achieve an adequate hematocrit response may depend on the severity of secondary hyperparathyroidism and the extent of bone marrow fibrosis (17). Because it may not be possible to evaluate the extent of myelofibrosis even after a bone marrow biopsy, we suggest that the extent of bone marrow fibrosis can be estimated by bone marrow expansion grading in BMIS.

In conclusion, BMIS may be useful for the detection of bone marrow expansion due to marrow fibrosis in renal osteodystrophy and for estimates of the extent of bone marrow fibrosis.

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Corresponding author:
Dong-kyu Cho, md, Division of Nephrology, Department of Internal Medicine, Kyungpook University Hospital, Samduck-dong 50, Jungku, Taegu 700-412, South Korea.