Single-Center Experience of Solitary Bone Plasmacytoma of the Vertebral Column in Comparison with Extramedullary Plasmacytoma of the Skull Base

Background Plasmacytomas are rare monoclonal B cell neoplasms, which can be subdivided into multiple myeloma (MM), solitary bone plasmacytoma (SBP), and extramedullary plasmacytoma (EMP). The upper aerodigestive tract and surrounding skull base region, due to rich lymphatics, is the most common site for EMP (accounts for 80% of head and neck cases). For SBP and EMP, there is a strong tendency for eventual conversion to MM. This study aimed to characterize and compare disease presentation, course and progression of SBP of the skull base with that of EMP of the vertebral column.

Design This is a single-center retrospective study that encompasses all patients with diagnosed solitary bone plasmacytoma or extramedullary plasmacytoma treated from 2000 to 2017.

Results A total of 24 patients with either SBP or EMP were identified. There were 12 patients with EMP of the skull or skull base, and 12 patients with SBP of the vertebral column. For the entire cohort, there were 20 male patients (83%) and 4 female patients. Average age at diagnosis was 55 years. Twenty-one of the 24 patients (88%) were current or former smokers at the time of diagnosis, with an average of 27 pack years. Most common presenting symptom for patients with SBP of the vertebral column included eight with pain (66.7%) and eight (66.7%) with lower extremity weakness. Among those with EMP, common presenting symptoms included mass effect and diplopia; only three patients (12.5%) presented with pain. Initial imaging modality for diagnosis included CT with or without MRI. Eight patients with SBP (66.7%) and four (33.3%) patients with EMP had initial surgical debulking. All patients with SBP and 11 patients with EMP (91.7%) were treated with radiation. Chemotherapy was more common in the SBP group (11, 91.6%) in comparison to the EMP group (5, 41.6%). Eleven patients with SBP (91.7%) and 7 with EMP (58.3%) eventually developed MM. Among SBP patients, two (16.7%) were initially diagnosed with MGUS and four (33.3%) had delayed development of MM at an average time of 7.8 months. Among EMP patients, one (8.3%) was initially diagnosed with MGUS and three (25%) had delayed development of MM at an average time of 17.3 months. Bone marrow transplant procedures were performed in four EMP patients (33.3%) with MM and one SBP patient (8.3%) with MM. Four patients with SBP (33.3%) and two with EMP (16.7%) were deceased at last follow-up, with an average follow-up length of 38 months.

Conclusion Plasmacytomas are a rare clinical entity with predilection for appearing as SBP in the vertebral column or EMP in the skull base region. While morphologically similar, the two categorizations do differ in regard to clinical presentation. SBP patients in our cohort were more prone to presenting with pain. More of the SBP patients eventually converted to multiple myeloma at a shorter time interval. SBP patients were not as likely to be BMT candidates in comparison to EMP patients. Our ultimate goal for this project would be to perform tissue microarray analysis to demonstrate potential biomarker differences that could serve as pharmacologic targets.