Bone density, bone markers and bone radiological features in mastocytosis.
Mastocytosis represents a spectrum of disease ranging from urticaria pigmentosa, an increase of dermal mast cells, to systemic mastocytosis involving bone marrow, skeleton, gastrointestinal canal, liver and spleen. Various skeletal manifestations have been observed in patients with mastocytosis  possibly reflecting different amounts of infiltrating mast cells and variation in the active substances they secrete. The major metabolite of histamine, methylimidazoleacetic acid in urine (MeImAA), is established as a good indicator of the mast cell mass in the body . New methods of measuring bone density and bone markers such as osteocalcin [serum bone-Gla-protein (BGP)] have made it possible to detect failure in bone mineral turnover and remodelling. BGP is a vitamin Kdependent gamma-carboxylated protein synthesized by osteoblasts. It seems to be of importance in initiating mineralization and is regarded as a biochemical indicator of bone turnover. The aim of this study was to compare patients with systemic mastocytosis and with urticaria pigmentosa in regard to bone density and biochemistry.
Material and Methods
Patients: Sixteen adult patients, six men and ten women (mean age 50.8 years), with mastocytosis were included in the study. Six patients had systemic mastocytosis and ten had urticaria pigmentosa. Four patients (three men and one woman) with an increased number of mast cells in the bone marrow and increased excretion of the major histamine metabolite in urine had pronounced radiological manifestations in the skeleton. Substantial clinical and laboratory data are presented (Table I). The subjects participating in the study had no endocrine disorder and no therapy involving steroids, oestrogens, vitamin D, parathyroid hormone or calcium supplements.
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The diagnosis of the skin disease was based on the clinical criteria for urticaria pigmentosa, e.g. multiple reddish brown maculae urticating after rubbing. The diagnosis of systemic mastocytosis was based on direct demonstration in bone marrow biopsy of an increased number of mast cells, marrow lesions containing mast cells, lymphocytes and eosinophils  and an increase in urinary excretion of methylimidazoleacetic acid . Clinical data included measurement of the excretion of this major histamine metabolite in urine (Table I). Information about physical activity, tobacco-smoking habits, previous and present physical activity, previous fractures, age at menarche and menopause, number of pregnancies, consumption of milk, cheese, coffee and medications was obtained from a self-administered questionnaire.
Bone mineral measurements: Measurement of bone mineral density (g/[cm.sup.2]) for comparison with age-matched controls was performed in the distal right radius and ulna with singlephoton absorptiometry (SPA) with a radiation source of [sup.125.I] (Osteometer DT 100). In the hip, anterior/posterior spine and total body, the same calculations were made by dual-energy X-ray absorptiometry (DXA) (Lunar DPX, Lunar Radiation Corporation, Madison WI). The DXA-method of bone mineral measurement was described by Fogelman and Ryan . As reference population we used data from a Danish study of 317 men and 1123 women aged 20-80 years randomly sampled from the local population register and measured at the Department of Clinical Chemistry, Glostrup Hospital, Denmark using the SPA-method as described by Christiansen et al..
Biochemical methods: The urinary excretion of methylimidazoleacetic acid (MeImAA) was calculated as MeImAA mmol/mol creatinine . Venous blood was sampled from an antecubital vein after a 30 minute rest in the sitting position. The subjects were asked to fast and not to smoke after 22 h 00 on the evening before the study. All individuals were treated by the same staff and by identical procedures. Serumosteocalcin (S-BGP) (reference interval 2-13,[mu]g/l) was determined by a double-antibody RUA method (International CIS, GIF-sur-Yvette Cedex, France). Serum alkaline phosphatase (S-ALP) (reference interval 0-5.0 [mu]kat/1), serum-tar/rate-resistant acid phosphatase (S-TRAP) (reference interval 0-60 nkat/l) were determined by standard methods . Serum-insulin-like growth factor (IGF-13 (reference interval 0.34-1.9kU/l) was registered on three consecutive days in one patient with severe vertebral fractures (case 4). One patient (case 13) refused venepuncture.
Radiographs, body mass index, bone marrow biopsies and iliac crest bone biopsies: Radiographs of the spine (T4-L5) were assessed by a radiologist for evidence of vertebral fracture in 13 patients of the total 16 patients (three patients were excluded on account of young age and lack of severe symptoms). Anteroposterior and lateral view of the thoracic and lumbar spine were obtained at a standard target-to-film distance of 105 cm. Moderate vertebral fracture was defined as an anterior/posterior (A/P) vertebral height ratio of 0.66 or less. Severe vertebral fracture was defined as a loss of vertebral height of more than 33% at both the anterior and posterior edges compared with the posterior edge of an adjacent vertebral body. These criteria have been suggested as a standard to reduce overdiagnosis of vertebral fractures . Body mass (of subjects wearing underwear only) and height were measured to the nearest 0.1 kg and 0.1 cm, respectively. Body mass index (BMI) was calculated as body weight divided by height squared . Bone marrow from crest biopsies was taken from all 16 subjects with mastocytosis using the long toluidine-blue staining technique for mast cells  and May Grunewald Giemsa staining for smears of bone marrow.
Trans-iliac crest bone biopsies after tetracycline labelling  were performed with a Burchardt instrument in the two men with the most severe mastocytosis and vertebral fractures and a BMD in the hip of 2.5 SD below the norm in order to exclude osteomalacia. The bone specimens were fixed in 70% ethanol and dehydrated with alcohol in increasing concentrations. Undecalcified sections were cut after being dehydrated and embedded in methylmethacrylate. The samples were sectioned in a hard sectioning Jung microtome Model K. Sections 5 [mu]m thick were stained according to Goldner's modification of Masson tricome staining. For evaluation of in vivo tetracycline labelling, 20 [mu]m-thick sections were cut.
Statistical analysis: Associations were evaluated first by linear regression. Correlation coefficients and significance were calculated. Fisher's two-sided permutation test was used to assess differences between groups .
Case 2: A 35-year-old physically active professional cook had noticed pain in the back after heavy lifts and had radiographic evidence of severe vertebral compressions. The patient showed a bone density of 57% of age matched controls in lumbar spine and 61% in the hip (Figure 1) an increased number of mast cells in bone marrow at crest biopsy and moderately increased urinary excretion of MeImAA (Table I). Iliac crest bone biopsy revealed no osteomalacia but moderate osteoporosis with normal trabecular volume but decreased osteoid surfaces and osteoid volume and increased mineral apposition rate (Table II). Normal S-BGP and increased level of S-ALP pointed to high bone turnover and increased resorption verified by a level of 60 nkatal/l in S-TRAP.
Case 4: A 40-year-old physician had urticaria pigmentosa and severe back pain and vertebral fractures sustained after heavy lifts (Table I). Bone marrow crest biopsy showed a slight increase in the number of mast cells and excretion of MeImAA indicated systemic mastocytosis. The patient had a rapid progression of the vertebral deformity with several severe vertebral fractures and low bone density especially in trabecular bone in the lumbar spine (50% of age-matched controls) and in the right hip (75% of age-matched controls) (Figure 1). Iliac crest bone biopsy demonstrated increased osteoid area, normal apposition rate and the marrow showed a varied and active structure of cells but no osteomalacia (Table II). Normal levels of S-BGP but increased S-ALP suggested increased formation inadequately compensating for resorption (Table I). IGF-1 was registered on three consecutive days at 0.29, 0.31 and 0.31kU/1 (reference interval 0.34-1.9kU/I). This finding confirmed a low level of IGF-1 corresponding with a low degree of bone formation .
Table II. Iliac bone biopsy in two men with mastocytosis and severe vertebral fractures and bone density 2.5 SD or more below control mean Case No. 2 4 Mineral apposition rate ([mu]m/day) 0.81 0.88 Osteoid surfaces (%) 6 15 Osteoid volume (%) 0 0 Trabecular bone volume (%) 15 19 Percentage of bone surface covered with osteoclasts 0 1 Reference datum for mineral apposition rate is 0.65[+ or -] 0.10 [mu]m/day .
Case 5: A 47-year old general labourer and ski runner with a 20-year history of urticaria pigmentosa had noticed aching pain in the back after exertion resulting in vertebral fractures (Table I). Excretion of MeImAA indicated systemic mastocytosis with moderately increased mast cell mass. Iliac crest biopsy showed mast cells, eosinophils and lymphocytes. Radiography of the thoraco-lumbar spine revealed osteopenia with one moderate vertebral fracture and some sclerosis. His trabecular bone density was 63% of age-matched controls in the lumbar spine and 73% of controls in the right hip. The mainly cortical bone of the distal radius was normal (Figure 1).
Case 14: A 72-year old woman had a 30-year history of mast cell disease in the skin, increased number of mast cells in the bone marrow and a large amount of MeImAA in her urine (Table I). She had back pain and radiographs showed osteosclerosis in the thoracic and lumbar spine as well as in the hip. Trabecular bone density was high in the lumbar spine at 229% of controls and in the hip at 152% of controls but cortical bone density in the distal radius was low at 68% of controls (Figure 2). Urinary MeImAA (Table I) was high. Many years of continuous smoking may have affected the formation of cortical bone in spite of a Body Mass Index of 27.0 (Table I).
Skeletal involvement: The bone density of subjects with urticaria pigmentosa seems to be normal but patients with systemic manifestations varied in having osteoporosis with vertebral fractures and decreased bone density or osteosclerosis with increased bone density. There was no significant correlation between urinary excretion of MeImAA and bone density in lumbar spine, hip, distal radius or total body (Table III) or with the indices of bone turnover (Table IV). Body Mass Index (BMI) was not significantly related to MeImAA excretion (Table III) or radiographic features (Table IV). MeImAA excretion was significantly higher (p < 0.01) in patients with increased density of trabecular bone (Figure 3) suggesting that histamine may enhance bone formation.
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Bone indices: The level of S-ALP was significantly (p < 0.05) higher in the three men with osteoporosis (cases 2, 4 and 5, Table I). They had low or normal values of S-BGP and slightly increased excretion of MeImAA. One woman with sclerotic changes in trabecular bone (case 14 in Table I) had high MeImAA excretion and an increased level of S-BGP compatible with osteosclerosis due to a high degree of bone formation. The high level of S-ALP was also compatible with enhanced bone formation.
Patients with systemic mastocytosis have increased numbers of mast cells in the bone marrow and radiographic lesions indicating skeletal involvement [1, 13, 14]. We have observed different types of skeletal lesions in patients with a moderate degree of systemic infiltration of mast cells compared with patients with a significant load of mast cells in the body. Three male patients with low bone density in both cortical and trabecular bone had sustained vertebral fractures. One female patient with sclerotic changes in trabecular bone of pelvis and thoraco-lumbar spine had an increased level of bone density in trabecular bone and low bone density in distal radius. Thus combinations of different patterns of skeletal involvement may occur and bone density measurement of trabecular (hip and lumbar spine) and cortical distal forearm (distal radius and ulna) bone can give contradictory results . Except for the distal forearm in men, the study showed a tendency to increased bone density in subjects with high excretion of MeImAA (Table III) suggesting that histamine may protect against osteoporosis (Figure 3).
The effect of mast cell mediators on osteoporosis and osteosclerosis in mastocytosis is not well understood. The various metabolites of the mast cells such as histamine, prostaglandin D2 and heparin may have different effects on bone remodelling to generate both osteoporosis and osteosclerosis [1, 15-22]. Our three male patients with vertebral fractures had only moderately increased amounts of mast cells in the body as assessed by only moderately increased MeImAA excretion. These patients had osteoporosis, while a female patient with a high excretion of MeImAA and elevated S-BGP had osteosclerosis of trabecular bone. The findings might indicate that mast cell mediators with influences on osteoclasts are dominant in patients with a moderate increase of mast cells, while the osteoblast-stimulating effect of histamine, reflected in high S-BGP, prevails in patients with high histamine metabolite excretion (Table I, Figure 2). Iliac crest bone biopsy in two subjects with osteoporosis confirmed active cell structure and increased bone turnover compared with individuals without bone disease . Earlier histomorphometric analyses of bone have shown that individual mast cells have been found near to or associated with osteoclasts or osteoblasts . The bone mediators of mast cells possibly participate in the regulation of bone remodelling or on the maturation of osteoclastic and osteoblastic precursors .
Bone markers S-BGP and S-ALP seemed to be higher in both men and women with increased excretion of MeImAA (Table III). In men with MeImAA less than 5mmol/mol creatinine, S-TRAP tended to be high which corresponds to increased resorption of bone (Table III); it was also high in subjects with osteoporosis (Table IV). S-BGP is increased in women without previous fractures  and increases with age especially after menopause . It is increased in patients with diseases associated with bone sclerosis  a finding which corresponds well with the patient presented as case 14 in the present study.
This study confirmed earlier reports that systemic mastocytosis can affect bone remodelling in various ways and demonstrated the need for radiography of bone and measurement of bone density in different sites as the disease may affect cortical and trabecular bone in different ways. Bone markers such as S-BGP, S-ALP, S-TRAP and IGF-1, iliac crest bone biopsy and histological measurements indicate high bone turnover in systemic mastocytosis. However, the number of patients studied is rather small; further work is needed to investigate how the different metabolites and immunological reactions associated with mast cells actually influence the osteoblasts and osteoclasts and their precursors in the bone remodelling process. Treatment with inhibitors of bone resorption such as oral bisphosphonates have been shown to be effective in systemic mastocytosis .
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This study was made possible by grants from the Swedish Council for Planning and Co-ordination of Research and the Swedish Medical Research Council.
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Authors' addresses C. Johansson, D. Mellstrom Department of Geriatric Medicine, Vasa Hospital, S-411 33 Goteborg, Sweden
G. Roupe Department of Dermatology,
G. Lindstedt Department of Clinical Chemistry,
Goteborg University, Sweden
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|Author:||Johansson, Christer; Roupe, Gosta; Lindstedt, Goran; Mellstrom, Dan|
|Publication:||Age and Ageing|
|Date:||Jan 1, 1996|
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