bubble_chart Overview

Plasmacytoma is a primary and systemic malignant tumor originating from the bone marrow, derived from B lymphocytes, and characterized by differentiation towards plasma cells. Solitary bone plasmacytoma is rare and can be cured.

bubble_chart Pathological Changes

1. Grossly, myeloma resembles tumors composed entirely or almost entirely of cells, appearing gray or red in color, soft in texture, and medullary, sometimes with cystic changes. The tumor tissue extensively infiltrates the medullary cavity, forming rounded tumor nodules that gradually enlarge and fuse. Some disseminated sexually transmitted disease lesions and most solitary sexually transmitted disease lesions can form massive tumor masses, often accompanied by hemorrhage, cystic changes, and necrosis. The tumor tissue penetrates the cortical bone and expands outward. In the spine, tumor expansion can compress the spinal cord and nerve roots.

2. Microscopically, the tumor tissue consists of densely packed cell clusters with almost no intercellular matrix.

The tumor cells can be identified as plasma cells, at least partially. These cells have abundant cytoplasm, deeply stained, basophilic, and well-defined boundaries. The nuclei are round, eccentric, and exhibit a clear perinuclear halo (a highly developed Golgi apparatus). The chromatin is clumped and distinctly oriented toward the nuclear membrane (cartwheel or leopard-skin pattern nuclei). Occasionally, square or triangular crystals may be observed within or outside the cytoplasm under electron microscopy. Surrounding these more or less typical plasma cells are some larger cells, which may be binucleated. Mitotic figures can be seen. Tumors with these characteristics are well-differentiated plasmacytomas.

In other cases, the tumor cells exhibit high atypia and are highly atypical. Large or giant cells predominate, with deeply stained cytoplasm and abundant vacuoles. The nuclei show marked pleomorphism, hyperchromasia, large nucleoli, and pathological mitotic figures. Giant cells containing multiple nuclei or bizarre nuclei may also be observed. These atypical cells are scattered among well-differentiated cells that can still be recognized as plasma cells.

bubble_chart Clinical Manifestations

The incidence rate is very high, higher than that of osteosarcoma. It is more common in males, with a male-to-female ratio of 1.5:1. It predominantly occurs in adults or the elderly, typically manifesting after the age of 40–50, rarely before 30, and never before adolescence.

Plasmacytoma is a systemic tumor originating from the bone marrow and will eventually involve most bones in the body, particularly areas with red marrow in adulthood. These regions include the spongy bones of the trunk, the skull, and the metaphyses of long bones, especially the spongy bones around the hip and shoulder joints.

The skeletal dissemination of plasmacytoma does not occur simultaneously or uniformly. At a certain stage of plasmacytoma, some bones are prone to invasion while others are not, or lesions may only be visible under a microscope.

It is not uncommon for the initial stage [first stage] of the disease to present as a single lesion confined to one bone segment. Such a plasmacytoma is termed solitary plasmacytoma. Although a single lesion may persist for years, sustained solitary plasmacytoma is rare, as almost all cases eventually disseminate to the skeleton and lead to death. The most common sites for solitary plasmacytoma are the spine (one or two vertebrae), followed by the trunk bones and the proximal femur.

The initial symptoms are vague or poorly localized and may persist for weeks or months, including grade I bone pain, constitutional weakness, weight loss, or grade I anemia. Patients often complain of lower back pain, which may extend to the chest. Spinal pain is often aggravated by movement, and paravertebral muscles may contract. Tapping the spinous process can induce pain. In some cases of lower lumbago, tumor tissue from multiple myeloma may compress nerve roots, causing radiating pain in the sciatic nerve or foot. With grade I trauma or no apparent cause, spinal pain can become very severe, indicating a pathological vertebral fracture. When vertebrae are extensively invaded, progressive or sudden spinal cord compression may lead to paraplegia, with or without vertebral compression fractures.

Pain and pathological fractures are uncommon as initial symptoms and usually occur in the advanced stages of the tumor.

In the advanced stage, symptoms may include swelling of superficial bones (ribs, sternum, clavicle), progressive weight loss, anemia, fever, high blood nitrogen, bleeding tendency, hypercalcemia and hyperuricemia, macroglossia due to extramedullary tumors and amyloidosis, and, in rare cases, renal insufficiency, which may progress to uremia in severe cases.

bubble_chart Auxiliary Examination

I. Laboratory Examination

1. Bone Marrow Smear

In the initial stage [first stage] of plasmacytoma, when the diagnosis is unclear, a bone marrow smear can often confirm the diagnosis, but a negative result does not rule out the possibility of plasmacytoma. If the smear shows 3% plasma cells, plasmacytoma should be suspected; if there are 10% plasma cells, the likelihood of plasmacytoma is high, though this can also be caused by diffuse or metastatic increases in plasma cells due to liver infections or bone metastases from cancer. If the percentage of plasma cells is even higher, up to 70%, and atypical plasma cells are observed alongside typical ones—such as those with large or double nuclei, or immature and atypical plasma cells—a diagnosis of plasmacytoma can be confirmed. The more advanced the disease, the higher the cytological detection rate.

2. Serum Protein

In most cases, serum globulin levels increase, and the albumin/globulin ratio is inverted. Even if total globulin levels are not elevated, immunoelectrophoresis may reveal a narrow, sharp peak in the α or γ globulin region, caused by an increase in monoclonal immunoglobulin. Electrophoretic changes are present in almost all disseminated cases, but may be absent in the initial stage [first stage], particularly in solitary plasmacytomas. In rare cases, serum electrophoresis shows no abnormalities, while urine electrophoresis does.

3. Bence-Jones Proteinuria

Detection using urine protein electrophoresis and immunoprotein electrophoresis is more sensitive than the traditional method of heating urine. The positive rate for Bence-Jones proteinuria is not high and may be seen in cases of plasmacytoma secreting light-chain globulins (K or L chains).

4. Hypercalcemia

Myeloma proliferation often causes diffuse bone resorption, leading to elevated blood calcium levels.

Hyperuricemia and azotemia are common. Hyperuricemia results from increased nucleic acid metabolism and can occur in all patients with excessive bone marrow proliferation. Azotemia is caused by renal damage from myeloma.

5. Peripheral Blood Changes

Manifested as anemia. White blood cell counts are generally unchanged, but in rare cases, significant leukocytosis may occur, even with large numbers of plasma cells—such cases are considered plasma cell leukemia.

II. X-ray Findings

Imaging findings have a latent period, and the extent of anatomical and imaging manifestations is disproportionate. Even when tumor tissue has diffusely invaded the bone marrow cavity, with no significant resorption of trabecular or cortical bone, imaging results may be negative.

Myeloma tumor tissue can destroy bone tissue, creating obvious porous changes, which appear as widespread osteoporosis and thinning of cortical bone on imaging, especially in the initial stage [first stage] of the disease and when the tumor invades the spine.

In the advanced stage of myeloma, tumor tissue not only extensively invades the medullary cavity but also forms disseminated tumor nodules. Initially small, these nodules grow and may fuse, determining the typical imaging features of plasmacytoma: small moth-eaten lesions, round punctate osteolysis, foamy changes from fused osteolytic areas, and extensive osteolytic lesions in the advanced stage. Typical osteolytic cavities lack sclerotic margins, while tumor tissue erodes cortical bone from within, thinning or even eliminating it in some areas.

The skull may show fine porous changes, resembling clustered styes, with a ground-glass appearance. As the disease progresses, multiple disseminated round osteolytic lesions of varying sizes may appear, progressively enlarging and fusing. The osteolytic areas have typical punched-out margins, giving the skull a hazy appearance on imaging.

In the spine, plasmacytoma can manifest as significant osteoporosis, with vertebral bodies showing compression changes, presenting a biconcave deformity, relative thickening of the intervertebral spaces, and increased curvature. In severe osteoporosis, osteolytic lacunae may be present. Typically, osteolytic lacunae can also be located in the posterior arches of the vertebral bodies and the ribs. The cortical bone of the spine and ribs may be very thin, with some areas showing grade I bubble-like expansion, and partial cortical bone interruption. Multiple compressed vertebral bodies are common. Lesions in the pelvis may exhibit similar changes.

In long bones, plasmacytoma may present as osteoporosis, moth-eaten destruction, and honeycomb or foam-like osteolysis. The tumor tissue infiltrates the cortical bone from the inner side, causing it to thin. The osteolytic lesions may fuse and enlarge, destroying the cortical bone and leading to pathological fractures, which primarily occur in the metaphysis, especially the proximal ends of the limbs. In advanced stages, the diaphysis may also be more or less invaded by tumor tissue.

In solitary plasmacytoma of bone, imaging shows a localized large osteolytic area. The osteolytic lesions may be of homogeneous origin, with or without cortical bone invasion; sometimes, they are formed by the fusion of multiple punctate osteolytic lesions; in other cases, they may cause bone expansion, presenting as thin soap-bubble-like osteolytic cavities.

Bone scans may be negative, even when imaging clearly reveals large lesions that appear positive.

bubble_chart Treatment Measures

The treatment is chemotherapy, and the most effective chemotherapeutic drugs are cyclophosphamide and melphalan, which can be combined with corticosteroids (prednisone), vincristine, doxorubicin, and other antitumor drugs.

When there is a large and localized osteolytic lesion, radiotherapy can relieve pain, alleviate spinal cord compression symptoms, and prevent pathological fractures. Young patients may undergo allogeneic bone marrow transplantation.

Surgery is suitable for spinal cord decompression in cases of initial paralysis and for the treatment and prevention of pathological fractures (osteosynthesis, bone cement fixation, prosthetic or joint prosthesis replacement).

Solitary myeloma is often treated with radiotherapy or surgical resection (wide excision) due to its characteristics, and a combination of radiotherapy and surgery may also be used.

bubble_chart Differentiation

The diagnosis of typical and advanced stage plasmacytoma is straightforward, but early-stage plasmacytoma is difficult to diagnose. In the early stages, plasmacytoma may be painless, with only mild or indistinct signs, a condition that can persist for months or even years.

Clinically, if patients over 40 years old present with skeletal dull pain or diffuse low back pain, lack of strength, pallor, or grade I weight loss, the possibility of myeloma should be suspected.

To confirm plasmacytoma, commonly required examinations include X-rays of the skull, spine, pelvis, and proximal limbs; bone scans; serum protein electrophoresis and immunoprotein electrophoresis (calcemia, uricemia); testing for Bence-Jones proteinuria and 24-hour urine protein electrophoresis (renal clearance rate); bone marrow aspiration from the sternum and iliac bone; and in cases of significant osteolysis, spinal cord compression, or solitary plasmacytoma, open or needle biopsy may be performed.

Serum immunoprotein electrophoresis is the most critical diagnostic test, revealing abnormal globulins in most cases, with solitary and diffuse plasmacytoma diseases rarely showing negative results. Urine protein electrophoresis may be positive even when serum protein electrophoresis is negative.

Bone marrow aspiration may yield negative results in the initial stage [first stage] of the disease or in solitary sexually transmitted disease cases. Bone marrow aspiration results may only show undifferentiated atypical components, and relying solely on these findings could lead to a misdiagnosis of lymphoma.