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Mass-forming extramedullary hematopoiesis in multiple myeloma: 18F-FDG PET/CT is useful in excluding extramedullary myeloma involvement

Abstract

Aims and background

Extramedullary hematopoiesis (EMH), a benign condition, is usually observed in patients with hematologic disorders. We report the first case of mass-forming EMH detected on a 18F-fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) scan in a patient with multiple myeloma (MM).

Methods

A 58-year-old woman underwent workup for bicytopenia, and was diagnosed with MM based on the results of bone marrow aspiration and serum protein electrophoresis. An 18F-FDG PET/CT scan revealed a paravertebral mass with mild FDG avidity, suggesting a tumorous condition.

Results

Biopsy was performed to exclude malignancy and the mass was eventually confirmed as EMH.

Conclusions

Differential diagnosis of a mildly FDG-avid paravertebral mass in MM should include EMH.

Tumori 2016; 102(Suppl. 2): e116 - e118

Article Type: CASE REPORT

DOI:10.5301/tj.5000437

Authors

Minjung Seo, Hawk Kim, Jae-Cheol Jo, Yunsuk Choi, Hee Jeong Cha, Ji-Hun Lim, Seol Hoon Park

Article History

Disclosures

Financial support: None.
Conflict of interest: None.

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Introduction

Extramedullary hematopoiesis (EMH) refers to hematopoiesis occurring outside the bone marrow, and can occur in patients with chronic anemia or myeloproliferative disorders. To our knowledge, it has not been reported in patients with multiple myeloma (MM) except for one interesting image of intracranial EMH (1).

Extramedullary hematopoiesis may occur anywhere in the body, and common sites include the spleen and the liver (2). However, it rarely presents as a posterior mediastinal mass, and clinical diagnosis is challenging in such cases (3).

We report a case of EMH detected by 18F-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT) in a patient with MM.

Case report

A 58-year-old woman was admitted to our center for lower chest and abdominal pain. Her laboratory findings showed bicytopenia with red and white blood cell counts of 5.3 M/μL and 3.12 K/μL, respectively. The hemoglobin and hematocrit levels were 5.3 g/dL and 20.0%, respectively, indicating anemia. The platelet count (220 K/μL) was within the normal range. Bone marrow aspiration and biopsy showed markedly increased plasma cells (Fig. 1, A-B-C). Serum protein electrophoresis showed a monoclonal peak of β2-globulin. Based on these findings, the patient was diagnosed with MM.

(A) Bone marrow aspiration shows increased plasma cells (Wright stain, × 400). (B) Bone marrow biopsy has increased cellularity with increased number of plasma cells (hematoxylin & eosin stain; magnification, × 400). (C) Immunohistochemical stain for CD138 shows increased plasma cells with clustering patterns.

Simple chest radiography showed an abnormal contour of the right paravertebral line. Enhanced chest CT revealed several incidental paravertebral masses at the level of the 7th-9th thoracic vertebrae, with the long axis measuring 4.9 cm. The well-demarcated lesions showed heterogeneous mild enhancement (Fig. 2A).

(A) Enhanced chest computed tomography (CT) and (B) nonenhanced CT portion of 18F-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT) reveal several paravertebral masses at the level of the 7th-9th thoracic vertebrae, with the long axis measuring 4.9 cm. The lesions are well-demarcated and show heterogeneous mild enhancement. (C) PET image of 18F-FDG PET/CT reveals mild FDG avidity (SUVmax = 1.7) in the paravertebral masses.

18F-FDG PET/CT revealed mild FDG avidity (SUVmax = 1.7) in the paravertebral masses (Fig. 2B and C). There were also multiple pathologic fractures involving the ribs, vertebrae, and pelvic bones.

For skeletal and paravertebral mass survey, magnetic resonance imaging (MRI) was performed. Signal intensities along whole vertebrae were heterogeneous, which was consistent with bone marrow infiltrating disease. Several compression fractures were also noted. The paravertebral masses were isointense on T1-weighted and slightly high on T2-weighted images. After gadolinium administration, mild homogenous enhancement was observed (Fig. 3, A-B-C-D).

Heterogeneous signal intensities along whole vertebrae are seen on magnetic resonance imaging, which was compatible with bone marrow infiltrating disease. (A) Several compression fractures are also noted. (B, C) The paravertebral masses are isointense on T1-weighted and slightly high on T2-weighted images. (D) There is mild homogenous enhancement after contrast injection.

To exclude posterior mediastinal malignancy, percutaneous needle aspiration was performed. Histologic analysis indicated EMH (Fig. 4). A final diagnosis of MM with thoracic EMH was made. The patient is currently being treated with thalidomide.

Histologic findings show myeloid, erythroid hematopoietic cells and megakaryocytes (hematoxylin & eosin stain; magnification, × 400).

Discussion

Extramedullary hematopoiesis, a compensatory mechanism for impaired hematopoiesis, is usually reported in thalassemia, sickle cell anemia, myelofibrosis, and myelodysplasia (2). It is a rare finding in MM (1) and its presentation as a thoracic paravertebral mass is even more unusual (3). To our knowledge, this is the first case of EMH presenting as a paravertebral mass that was detected by 18F-FDG PET/CT in a patient with MM.

Differential diagnoses of paravertebral masses include neurogenic tumors, paravertebral abscesses, and malignant neoplasms. Histologic confirmation is the gold standard for diagnosis. However, it is an invasive procedure with a risk of hemorrhage, particularly in EMH. An adequate noninvasive workup may be clinically useful in the evaluation of the paravertebral masses (4).

Among the noninvasive imaging techniques, the ones most commonly used for diagnosis of EMH are CT and MRI. On chest X-rays, such masses show a lobulated, double-contour cardiac silhouette. They are reported as lobulated homogenous paravertebral masses with smooth margins and may or may not be enhanced on CT scans (5). On MRI, EMH masses may show intermediate T1 and T2 signal intensities (6). They may appear heterogeneous or homogeneous, depending on the level of adipose cell infiltration (7). The imaging findings in our case were consistent with all of the above EMH characteristics.

The characteristics of EMH on 18F-FDG PET/CT have not yet been established, with only 2 cases reported to date (8, 9). There is currently no report regarding 18F-FDG PET/CT scans of EMH mimicking malignancy in MM. In one report describing thoracic EMH diagnosed upon 18F-FDG PET/CT in a thalassemia patient, the authors found a 13-cm paravertebral mass at the posterior-inferior mediastinum with mild FDG avidity (SUVmax = 2.5) (8). Another report of a thalassemia patient revealed multiple paravertebral thoracic masses with mild to moderate FDG avidity (SUVmax not indicated) (9). Although the reported data are limited and apply to thalassemia, our findings are consistent with those of previous reports. All these findings suggest that EMH presenting as a paravertebral mass shows mild FDG avidity, making this a characteristic that may be helpful in differentiating it from other malignancies with high FDG avidity.

Patients with EMH usually have a known underlying condition. The patient in our case was diagnosed with MM after presenting with bicytopenia. The patient's findings suggest that the cause of EMH was anemia. If a paravertebral mass is found in such patients and it shows mild FDG avidity on 18F-FDG PET/CT, EMH may be included in the differential diagnosis.

In conclusion, EMH as a paravertebral mass may be detected in MM and is likely to show mild FDG avidity. When paravertebral masses are incidentally detected in patients with MM, 18F-FDG PET/CT might be useful in the differential diagnosis if histologic confirmation is clinically impossible.

Disclosures

Financial support: None.
Conflict of interest: None.
References
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Authors

Affiliations

  • Department of Nuclear Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan - Korea
  • Department of Hematology and Cellular Therapy, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan - Korea
  • Department of Pathology, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan - Korea
  • Department of Laboratory Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan - Korea

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