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AJR 2002; 179:1235-1237
© American Roentgen Ray Society

Original Report

FDG Positron Emission Tomography in Patients with Systemic Mastocytosis

Georg Zettinig1, Alexander Becherer1, Monika Szabo1, Martin Uffmann2, Robert Dudczak1, Peter Valent3 and Kurt Kletter1

1 Department of Nuclear Medicine, University of Vienna, Währinger Gürtel 18-20, A-1090 Wien, Austria.
2 Department of Radiology, University of Vienna, A-1090 Wien, Austria.
3 Department of Internal Medicine I, University of Vienna, A-1090 Wien, Austria.

Received March 30, 2002; accepted after revision June 17, 2002.

 
Address correspondence to G. Zettinig.


Abstract
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 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
OBJECTIVE. Systemic mastocytosis is a hematologic neoplasm characterized by abnormal accumulation and growth of mast cells in one or more organ systems. We analyzed five patients with systemic mastocytosis referred for FDG positron emission tomography who had biopsy-proven mast cell infiltrates in various organs.

CONCLUSION. Our findings indicate that FDG positron emission tomography is not useful for staging and follow-up of aggressive systemic mastocytosis.


Introduction
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 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Systemic mastocytosis is a hematologic neoplasm characterized by abnormal accumulation and growth of mast cells in one or more organs. The clinical picture is variable, ranging from asymptomatic or indolent courses to highly aggressive cases with a short survival rate [1, 2]. In aggressive systemic mastocytosis, the proliferation of mast cells leads to consecutive organ failure, and the patients can show a variety of clinical signs and symptoms such as hepatosplenomegaly; lymphadenopathy; impaired liver function; liver fibrosis; ascites; osteolytic, sclerotic, or osteoporotic bone lesion fractures; bone marrow fibrosis; or decrease in bone marrow function [3]. Systemic mastocytosis can either present as an isolated hematologic disease or be accompanied by other hematologic malignancies such as myeloproliferative or myelodysplastic syndrome or acute leukemia [1].

Staging of systemic mastocytosis includes bone marrow biopsy, radiography of the chest and the skeleton, bone scanning, sonography of the abdomen, and endoscopy of the gastrointestinal tract [4,5,6]. A more extensive staging may be required in cases of suspected aggressive disease [7].

Positron emission tomography (PET) with FDG is an excellent imaging tool for various lymphohematopoietic neoplasms. However, to the best of our knowledge, no data report FDG PET features in patients with this disease. The aim of this retrospective analysis was to evaluate FDG PET in aggressive systemic mastocytosis.


Materials and Methods
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 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
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We analyzed five patients (three men and two women; age range, 23-53 years; median age, 47 years) with systemic mastocytosis who were referred for FDG PET to our department between 1998 and 2001. Four of the patients were imaged before any treatment at the initial staging of the disease, and one patient had PET while undergoing treatment with interferon-{alpha}. The diagnosis was established according to published criteria [3] on the basis of bone marrow biopsy, complete differential blood count, and other clinical and laboratory parameters. All patients had extended workups including radiography of the bones, upper gastrointestinal tract investigation, and sonography of the liver and spleen. All patients were examined for signs of progressive infiltration of mast cells into lymphohematopoietic organs and for other hematologic abnormalities [3].

Aggressive systemic mastocytosis was diagnosed in three patients. In two of them, the disease was associated with chronic myelomonocytic leukemia. In one patient, smoldering systemic mastocytosis was diagnosed, and the remaining patient had indolent systemic mastocytosis. Bone marrow biopsy showed a mast cell infiltration with a range between 15% and 70%. Biopsy-proven infiltration of the liver was found in two patients, and three patients showed cutaneous mast cell infiltrates. Three patients had radiologically diagnosed skeletal lesions. Larger osteolyses were biopsied, confirming the presence of mast cell infiltrates. One patient had generalized lymphadenopathy; and in four patients, splenomegaly was diagnosed.

All images were performed on a dedicated fullring PET scanner (Advance; General Electric Medical Systems, Milwaukee, WI) following the same protocol. Patients received a median activity of 365 MBq (range, 350-380 MBq) of FDG IV after fasting for at least 6 hr. At the time of radiotracer application, the patients' median glucose level was 94 mg/dL (range, 67-128 mg/dL). Forty minutes after injection, an emission scan from the upper legs to the head was obtained. Scanning time was 5 min per step, and acquisition was performed in two-dimensional standard mode with a matrix size of 128 x 128. Images were reconstructed as filtered back-projection using a Hanning filter with a cutoff of 12. The PET scans were interpreted independently by three nuclear medicine physicians.


Results
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 Materials and Methods
 Results
Discussion
 References
 
All biopsy-proven lesions had normal findings on FDG uptake, and in the radiologically diagnosed osteolytic lesions, radiotracer distribution findings were also normal. The patients with splenomegaly also had a normal FDG metabolism, with the exception of one patient who showed slightly increased radiotracer uptake in the enlarged spleen.

The only abnormal finding was a moderately increased radiotracer accumulation in the proximal humeri of three patients that showed no correlation with other imaging methods (Figs. 1A,1B,1C,1D and 2A,2B,2C).



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  		Fig. 1A. —52-year-old woman with aggressive systemic mastocytosis with splenomegaly; biopsy-proven mast cell infiltration of liver; and multiple skeletal mast cell infiltration of pelvis, both femora, spine, ribs, and scapulae. One day before positron emission tomography (PET), pathologic fracture of right femoral neck was diagnosed, leading to right-sided hip replacement 5 days after PET. Histology of femoral head revealed 50% bone marrow infiltration. In this patient, aggressive systemic mastocytosis was associated with chronic myelomonocytic leukemia. Coronal maximum-intensity-projection FDG PET image shows no signs of infiltration in known lesions. However, moderate radiotracer accumulation was present in both proximal humeri (arrows) that was also seen in two other patients and did not show any correlation with other imaging methods.

 


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  		Fig. 1B. —52-year-old woman with aggressive systemic mastocytosis with splenomegaly; biopsy-proven mast cell infiltration of liver; and multiple skeletal mast cell infiltration of pelvis, both femora, spine, ribs, and scapulae. One day before positron emission tomography (PET), pathologic fracture of right femoral neck was diagnosed, leading to right-sided hip replacement 5 days after PET. Histology of femoral head revealed 50% bone marrow infiltration. In this patient, aggressive systemic mastocytosis was associated with chronic myelomonocytic leukemia. Radiographs show inhomogeneous pattern with mixed small osteolytic and osteoblastic areas in pelvis, both femora (B), and spine (C), as typically seen in mast cell infiltration. Note right femoral neck fracture.

 


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  		Fig. 1C. —52-year-old woman with aggressive systemic mastocytosis with splenomegaly; biopsy-proven mast cell infiltration of liver; and multiple skeletal mast cell infiltration of pelvis, both femora, spine, ribs, and scapulae. One day before positron emission tomography (PET), pathologic fracture of right femoral neck was diagnosed, leading to right-sided hip replacement 5 days after PET. Histology of femoral head revealed 50% bone marrow infiltration. In this patient, aggressive systemic mastocytosis was associated with chronic myelomonocytic leukemia. Radiographs show inhomogeneous pattern with mixed small osteolytic and osteoblastic areas in pelvis, both femora (B), and spine (C), as typically seen in mast cell infiltration. Note right femoral neck fracture.

 


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  		Fig. 1D. —52-year-old woman with aggressive systemic mastocytosis with splenomegaly; biopsy-proven mast cell infiltration of liver; and multiple skeletal mast cell infiltration of pelvis, both femora, spine, ribs, and scapulae. One day before positron emission tomography (PET), pathologic fracture of right femoral neck was diagnosed, leading to right-sided hip replacement 5 days after PET. Histology of femoral head revealed 50% bone marrow infiltration. In this patient, aggressive systemic mastocytosis was associated with chronic myelomonocytic leukemia. In comparison with adjacent ribs, radiograph shows only subtle changes in left proximal humerus.

 


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  		Fig. 2A. —53-year-old man with aggressive systemic mastocytosis with splenomegaly, ascites, and biopsy-proven mast cell infiltration of liver, skin, and skeleton. Sagittal gradient-echo T1-weighted MR image (TR/TE, 180/4) of lumbar spine shows hypointense bone marrow compared with intervertebral disks, suggesting deposition of mast cells and partial replacement of fatty marrow.

 


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  		Fig. 2B. —53-year-old man with aggressive systemic mastocytosis with splenomegaly, ascites, and biopsy-proven mast cell infiltration of liver, skin, and skeleton. Sagittal inversion recovery MR image (500/30) shows hyperintense bone marrow indicating replacement of normal fat.

 


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  		Fig. 2C. —53-year-old man with aggressive systemic mastocytosis with splenomegaly, ascites, and biopsy-proven mast cell infiltration of liver, skin, and skeleton. Sagittal FDG positron emission tomography image shows normal radiotracer distribution.

 


Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Our analysis of FDG PET in five patients who were well-staged with systemic mastocytosis, including three with aggressive disease, showed normal FDG findings for all known lesions. The reason for the completely normal FDG metabolism in all lesions of our patients remains unclear. Mast cells in patients with aggressive systemic mastocytosis can be quite immature [8], and FDG PET has been well established as an excellent imaging tool for a variety of malignancies. The most important hematologic indication for FDG PET is lymphoma [9]. FDG PET is well established for monitoring patients with both aggressive and indolent subtypes of this disease with the exception of lymphomas that do not occur as bulky diseases, such as lymphomas of the mucosa-associated lymphoid tissue. This subtype is not visualized on FDG PET [10]. The value of FDG PET also seems to be limited in other hematologic disorders with diffuse tissue infiltration such as leukemia; our two patients with associated chronic myelomonocytic leukemia had a normal radiotracer distribution. The diffuse proliferation of mast cells might have been the cause of FDG PET failing to reveal organ infiltration in our patients.

Although the incidence of systemic mastocytosis in the general population is rare, these patients are normally referred to specialized centers for further treatment. Our hospital is a tertiary referral center, and we see approximately 10 patients with newly diagnosed systemic mastocytosis per year. Only a minor subset of them have aggressive disease; in those patients with organopathies, we must determine whether the organopathies are caused by aggressive growth of mast cells. Various imaging methods are available [4,5,6,7], but in individual patients, the diagnosis may remain unclear. In addition, aggressive systemic mastocytosis may be accompanied by other hematologic malignancies such as myeloproliferative or myelodysplastic syndrome or acute leukemia [1].

Improved staging methods for systemic mastocytosis are required, but FDG PET could not reveal any documented lesion in our patients. The identical findings of normal FDG metabolism in all lesions of all our patients indicate that FDG PET is not useful for imaging organ infiltration in aggressive systemic mastocytosis. FDG PET should therefore not be included in the clinical staging process in these patients.


References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Valent P. Biology, classification and treatment of human mastocytosis. Wien Klin Wochenschr 1996;108:385 -397[Medline]
  2. Metcalfe DD. Classification and diagnosis of mastocytosis: current status. J Invest Dermatol 1991;96:2S -4S[Medline]
  3. Valent P, Horny HP, Escribano L, et al. Diagnostic criteria and classification of mastocytosis: a consensus proposal. Leuk Res 2001;25:603 -625[Medline]
  4. Rosenbaum RC, Frieri M, Metcalfe DD. Patterns of skeletal scintigraphy and their relationship to plasma and urinary histamine levels in systemic mastocytosis. J Nucl Med 1984;25:859 -864[Abstract/Free Full Text]
  5. Huang TY, Yam LT, Li CY. Radiological features of systemic mast-cell disease. Br J Radiol 1987;60:765 -770[Abstract]
  6. Avila NA, Ling A, Worobec AS, Mican JM, Metcalfe DD. Systemic mastocytosis: CT and US features of abdominal manifestations. Radiology 1997;202:367 -372[Abstract/Free Full Text]
  7. Avila NA, Ling A, Metcalfe DD, Worobec AS. Mastocytosis: magnetic resonance imaging patterns of marrow disease. Skeletal Radiol 1998;27:119 -126[Medline]
  8. Parwaresch MR, Horny HP, Lennert K. Tissue mast cells in health and disease. Pathol Res Pract 1985;179:439 -461[Medline]
  9. Becherer A, Mitterbauer M, Jaeger U, et al. Positron emission tomography with [18F]2-fluoro-D-2-deoxyglucose (FDG-PET) predicts relapse of malignant lymphoma after high-dose therapy with stem cell transplantation. Leukemia 2002;16:260 -267[Medline]
  10. Hoffmann M, Kletter K, Diemling M, et al. Positron emission tomography with fluorine-18-2-fluoro-2-deoxy-D-glucose (F18-FDG) does not visualize extranodal B-cell lymphoma of the mucosa-associated lymphoid tissue (MALT)-type. Ann Oncol 1999;10:1185 -1189[Abstract/Free Full Text]

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This Article
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