Systemic mastocytosis

Introduction

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 [1] 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 [2]. 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.

[TABULAR DATA I OMITTED]

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 [3] and an increase in urinary excretion of methylimidazoleacetic acid [2]. 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 [4]. 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.[5].

Biochemical methods: The urinary excretion of methylimidazoleacetic acid (MeImAA) was calculated as MeImAA mmol/mol creatinine [3]. 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 [6]. 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 [7]. 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 [8]. Bone marrow from crest biopsies was taken from all 16 subjects with mastocytosis using the long toluidine-blue staining technique for mast cells [9] and May Grunewald Giemsa staining for smears of bone marrow.

Trans-iliac crest bone biopsies after tetracycline labelling [10] 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 [11].

Results

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 [12].

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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