Presentation
A patient with a history of multiple myeloma presents with left arm swelling and pain.
Patient Data
There is mass-like enlargement of the triceps, brachialis, and biceps muscles with soft tissue nodularity in the subcutaneous fat anterolateral in the mid portion of the upper arm.
There is a focal area of soft tissue replacement of the marrow of the humerus, which is suspicious for a small focus of myeloma given the history, but there is no bony destruction of the cortex or contiguous extension outside the bone into the soft tissues.
The deep subcutaneous nodularity and intramuscular mass/masses appear to be separate processes from the small bony tumor in the humerus.
There is a small bone-confined tumor/myeloma within the marrow of the mid-humerus, corresponding to the CT finding. No bony destruction or invasion into the soft tissues.
However, this is mass-like enlargement from discrete enhancing masses within the intramuscular compartments of the upper arm involving the triceps, biceps, and brachialis that is T1 isointense, T2 hyperintense, and markedly enhancing with an expansile appearance. These masses also demonstrate extension outside the musculature into the deep subcutaneous space, corresponding to the CT findings.
There is a solid-appearing mass-like lesion within the soft tissue of the left upper extremity.
Pathology findings (FNA):
Aspirate smears and core biopsies consist of sheets of relatively uniform plasma cells. The plasma cells are diffusely positive for CD138 with aberrant expression of CD3. CD20 and cyclin D1 are negative. Kappa light chain in situ hybridization (ISH) is positive. Lambda ISH is negative.
Impression:
Plasma cell neoplasm with kappa light chain restriction and aberrant expression of CD3.
Case Discussion
Multiple myeloma is a malignant clonal expansion of plasma cells that accounts for 10% of hematologic malignancies 1. Typically, multiple myeloma can arise from a clinically insignificant proliferation of plasma cells known as monoclonal gammopathy of undetermined significance 1. The worldwide incidence of multiple myeloma is between 0.54 and 6.3 per 100,000 and accounts for 2% of cancer diagnoses in the US 2-3. The incidence of multiple myeloma is on the rise, with a 126% increase in incidence over the last thirty years 3.
Extramedullary involvement in multiple myeloma is an aggressive form of multiple myeloma defined by the ability of the plasma cells to clone independently of the bone marrow environment 4. Extramedullary involvement is often restricted to soft tissue plasmacytomas that have no contact with bony structures; however, no set criteria have been defined 4. In patients with diagnosed multiple myeloma, the incidence rates of extramedullary involvement range from 0.5% to 4.8% 4. Multiple myeloma patients with extramedullary involvement often have poorer outcomes when compared to patients without, which increases the importance of early detection 4. Retrospective studies have revealed a lower survival outcome for patients with plasmacytomas (both paraskeletal and no bony contact) when compared to patients without any extramedullary involvement (63% vs. 80% 5-year overall survival) 4-5.
In our case, the patient had a diagnosis of multiple myeloma (without remission) one year prior to presenting to our hospital. Our patient presented with left arm swelling and pain and underwent imaging and a biopsy. The nonspecific signs on the CT/ultrasound combined with the history of multiple myeloma led to MRI imaging and a biopsy. The biopsy was positive for a soft tissue plasma cell neoplasm of the upper arm with kappa light chain restriction and aberrant expression of CD3. The patient started treatment with Daratumumab.
Future radiologists encountering a soft tissue mass on imaging in a patient with a history of multiple myeloma should include extramedullary myelomatous deposits in the differential diagnosis.
This case was edited and provided by Ashwin Hampole, MD.
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