Solitary Bone Plasmacytoma: The Unusual Case with Involvement of Adjacent Disc Space


 Background: Solitary plasmacytoma of the bone (SPB) is a rare manifestation of plasma cell tumor that usually presents as a osteolytic lesion mainly localized within the axial skeleton and the back pain is a common clinical feature.Case presentation: This case report discussed a 57-year-old male presented with low back pain caused by SBP. In this case, there is an even rarer phenomenon presented as osteolytic destruction in T7 to T9 vertebral bodies with involvement of adjacent disc spaces. This case report provided a comprehensive description of the radiographic assessment, medical management, and differential diagnosis.Conclusions: This is the first discussion focusing on differential diagnosis between spinal neoplasm and infectious diseases about SBP with involvement of adjacent disc space.


Background
The most common complaints of patients with spinal disease is back pain, which has a series underlying cause such as infection and neoplasm.. Consequently, differentiating these causes of back pain is paramount to con rm diagnosis and administrate medical management.. This case report describes a patient presented with low back pain caused by a solitary bone plasmacytoma (SBP). SBP is characterized by a localized proliferation of neoplastic plasma cells in the absence of signi cant bone marrow plasma cell in ltration, which occurs primarily in red marrow-containing bones such as vertebrae, femurs, pelvis, and ribs [1][2][3]. To the best of our knowledge, there is only one report in the literature describing SBP in vertebra with involving adjacent disc space [4]. The differential diagnosis of vertebral lesion with adjacent disc space involvement usually considers spinal infection, but the possibility of a SBP associated with adjacent disk space involvement is seldom considered. This case report provides a comprehensive description of the case suffered SBP in thoracic vertebral region, which involved adjacent disc space, and discusses the differential diagnosis from spinal infection.

Case Presentation
A 57-year-old male was admitted with a chief complaint of intermittent pain in the back for the past 2 year. The pain was non-radiating and not responding to conservative medical management. His past medical history and ndings of a physical examination were unremarkable. Results of his blood chemistry and routine blood tests were within normal limits. A urine analysis showed normal values. Old tuberculin (OT) test and brucellosis agglutination test were negative. His lateral spine radiograph showed osteolytic destruction from T7 to T8 with intervertebral space stenosis. A computed tomography scan (CT) revealed slight expansile osteolytic destruction in T8 with sclerosis margin, extension to T7 and T9 and adjacent disc space destruction. Magnetic resonance imaging (MRI) showed the lesion involved primarily the T8 vertebral body rightly, directive contiguous extension to T7-T9 with disc space destruction. The lesion appeared mildly isointense on T1 weighted images, hyperintense on T2 weighted images, and intense homogeneous enhancement on T1 weighted post IV Gad contrast images (Fig. 1).
Upon performing transpedicular needle biopsy from T8 showed a small amount of fragments of bone trabeculae and denatured collagenous bers with in ammatory exudates (Fig. 2). As spine existing instability, surgery was scheduled with discussion at multidisciplinary meeting without preoperative con rmation of diagnosis. Under general anesthesia, the patient was subjected to the posterior fusion procedure from T6-T1 and open biopsy of the lesion at the 20th day after hospitalization. The open biopsy samples were sent to pathology and the histological ndings indicated a large amount of plasma cell in ltration (Fig. 3). Immunohistochemical studies showed sheets of lambda positive CD38, CD138 positive plasma cells (Fig. 4). Postoperative positron emission tomography-CT (PET-CT) with 18-urodeoxyglucose showed a highly hypermetabolic lesion in T7 to T9 with a standard uptake value of 10.9 but did not detect any other lesions or distant metastasis other than a T7 to T9 lesion (Fig. 5). The peripheral smear and bone marrow aspirate were within the normal limits. Urine Bence-Jones protein was negative. Based on the pathology results, laboratory studies and no other sites of bone involvement of imaging data, the patient was diagnosed with SBP. Forty-ve days after the operation, the oncology course of treatment was administered with a total of 4000 Gy to the T7-T9 vertebral levels over a 20 day period.Over a 2-month follow-up, the patient has been pain-free.

Discussion
SPB is a rare hematologic malignancy, which is de ned by the presence of a single osteolytic lesion due to monoclonal plasma cell in ltration, with or without soft-tissue extension [2]. The median age at the diagnosis is 55 years and males are more frequently affected than females. The lesion is often present for many years as a single lesion; however, it can eventually progress to multiple plasmacytomas within 3 years [5]. The most common site of SBP involving is the vertebrae, especially thoracic vertebrae, and the back pain is a common clinical feature due to lesion compression [6,7]. Diagnostic criteria of a SPB include pathological proven solitary lesion, normal bone marrow with no evidence of clonal plasma cells, normal skeletal survey and MRI ( or CT ) of spine and pelvis ( except for the primary solitary lesion ), absence of end-organ damage [1]. Our case meets all these criteria for the diagnosis of SPB. Nonetheless, clinical aspects overlap, thus making directed diagnostic and therapeutic strategies di cult. Besides the above criteria of diagnosis, imaging studies play an important role in the diagnostic, treatment considerations and prognostic aspects [1]. However, imaging studies may not always provide a conclusive diagnosis. SBP has an osteolytic appearance on plain radiographs, and an expansile osteolytic lesion with marked enhancement on CT or MRI [2]. In the published nding, SBP of spine could show curved coarse trabeculae with hypertrophic sclerosis, forming"mini brain sign"which had certain characteristics. This appearance may be correlated with the less aggressive nature of SBP comparing with other malignant tumors that aggressively destroy the bone with no radiological evidence of bone repair features such as sclerosis and thickening [8,9]. In our case, we could not observe this similar signs. To the best of our knowledge, most studies did not report the imaging presentation of SBP involving adjacent disc space, there was only one reported case of SBP with involving adjacent disc space by direct extension [4]. Afonso and colleagues reported a 41-year-old woman with SBP, her spine CT revealed areas from T12 to L2 with vertebrae and disc space destruction. The case report mainly focused on lesion's CT and MRI ndings, without describing differential diagnosis in diseases with involving adjacent disc space, such as spinal neoplasms and infections.
Usually spinal lesions associated with a poorly de ned vertebral body endplate, involvement of intervertebral disc space, presence of paravertebral abscesses and involvement of two contiguous vertebral bodies are suggestive of spinal infection, whereas spinal lesions associated,well-preserved disc space, destroyed vertebral bodies with solid extraosseous soft tissue, or non consecutive multifocal involvement of spine are suggestive of spinal neoplasm [10,11]. However, one study found 2% malignant spinal lesions with disc involvement [12], SBP with adjacent disc space destruction may be due to aggressive traits of primary plasmacytoma presenting in ltration and destruction of adjacent bone, muscle, fat and vascular encasement. [13,14]. In an approach to such patients with involving adjacent disc space, differential diagnosis should include neoplasm and bacterial infection. In some conditions of spinal infections, patients' symptoms with no fever can be very similar to those of other spinal lesions, and imaging ndings can be non-speci c or atypical, laboratory examinations including white blood cell count (WBC), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are inconclusive, thus differential diagnosis is warranted [15,16]. In these cases, biopsy is paramount to con rm diagnosis.
However, a study reported the presumed aetiology in 18% of the cases was not con rmed on pathological examination [17]. A recent metanalysis reported the sensitivity of CT-guided percutaneous needle aspiration biopsy was 52.2% (95% CI, 45.8-58.5) for the diagnosis of spinal infections [18]. Additionally, the presentation of disc involvement is nonspeci c feature of spinal infection, but is compatible with solid neoplasms, as shown the case in the present report. Hence, differential diagnosis between spinal neoplasms and infections is more di cult and complicated. The diagnostic approach for the patients with spinal lesions should include a complete medical history, physical examination, necessary laboratory examinations and imaging evaluations during which possible risk factors for infection and neoplasm must be investigated and identi ed. Spine imaging evaluation should be essential to careful observation at or around the each portion of vertebral bodies, such as facet joints, epidural space, and muscular structures of spine. In some cases, repeat or open biopsy may be required as it is the only reliable method to distinguish neoplasms and infections.

Conclusions
In conclusion, there is a few of report in the literature depicting SPB with disc involvement regarding to the differential diagnosis from spinal infections. Our case report may help recognition of this rare sign of the disease, thus avoiding misdiagnosis and inadequate treatment.

Declarations
Ethics approval and consent to participate Not applicable. Figure 1 Lateral spine radiograph demonstrated osteolytic destruction of T7 and T8 vertebral body with intervertebral space stenosis (a). Mid-sagittal CT of thoracic spine suggested slight expansile osteolytic destruction in T8 vertebral body with sclerosis margin, extension to T7 and T9 vertebral body and adjacent disk-space destruction (b). The corresponding thoracic spine MRI revealed the lesion exhibiting mildly isointense on T1 weighted images (c), hyperintense on T2 weighted images(d), and intense homogeneous enhancement on T1 weighted post IV Gad contrast images (e).

Figure 2
Hematoxylin and eosin (H&E) stained biopsy specimen showed a small amount of fragments of bone trabeculae and denatured collagenous bers with in ammatory exudates (100×).   PET-CT scan showed the hypermetabolic lesion in T7 to T9.