Multiple Myeloma and Plasma Cell Dyscrasias

Clonal Plasma Cell Proliferation and Genetic Abnormalities

• Neoplastic transformation originates from a single plasma cell clone acquiring sequential genetic mutations that confer growth advantage and resistance to apoptosis
• Primary cytogenetic abnormalities include t(4;14) (FGFR3/IGH translocation), t(14;16) (MAF/IGH), t(14;20) (MAFB/IGH), and del(17p) (TP53 loss)—the latter representing high-risk disease with poor prognosis
• Hyperdiploidy (trisomy of chromosomes 3, 5, 7, 9, 11, 15, 19, 21) represents a separate pathway and generally confers better prognosis than translocations
• Secondary mutations accumulate in KRAS, NRAS, TP53, DIS3, and FAM46C, driving progression from precursor states to aggressive disease
• Activation of NF-κB and MAPK signaling pathways promotes proliferation and survival
• BRAF V600E mutations occur in subset of cases and define a distinct molecular subtype

Bone Marrow Microenvironment and Immune Evasion

• Malignant plasma cells preferentially home to and proliferate within the bone marrow microenvironment, establishing protective niches through interaction with bone marrow stromal cells (BMSCs)
• BMSCs secrete IL-6, FGF, VEGF, and TNF-α, providing essential paracrine growth signals
• Adhesion molecules (VLA-4, ICAM-1, NCAM) mediate tumor-stromal interactions that promote drug resistance
• Malignant cells evade immune surveillance through PD-L1 expression, recruitment of regulatory T cells (Tregs), and suppression of natural killer (NK) cells
• Dysfunction of the immune synapse allows escape from cytotoxic T lymphocytes
• Bone marrow angiogenesis is promoted, supporting nutrient delivery and drug resistance

Monoclonal Protein Production and Organ Damage

• Neoplastic plasma cells produce excessive quantities of monoclonal immunoglobulin (M-protein) with one heavy chain type (IgG, IgA, IgD, IgE, IgM) and one light chain type (kappa or lambda)
• Approximately 20% of cases produce only free light chains (FLC) without intact immunoglobulin, termed "light chain myeloma"
• Light chain proteins are toxic to the proximal renal tubules, causing light chain cast nephropathy (myeloma kidney) through precipitation in acidic, protein-rich environment
• Hyperviscosity from elevated protein concentration causes rheological dysfunction, particularly with IgA and IgM
• Monoclonal proteins may exhibit cryoglobulin properties or act as amyloid precursors (AL amyloidosis)
• Immunoparesis results from suppression of normal immunoglobulin production by malignant clones, predisposing to infection

Osteolytic Bone Disease

• RANKL (receptor activator of NF-κB ligand) secretion by myeloma cells and BMSCs activates RANK on osteoclasts, driving bone resorption
• Osteoprotegerin (OPG) suppression by myeloma cells shifts the RANKL/OPG balance toward resorption
• DKK-1 and sFRP-2 (Wnt pathway antagonists) produced by myeloma cells inhibit osteoblasts, preventing bone formation
• Result is uncoupled bone remodeling with excessive resorption and impaired formation, creating characteristic punched-out lytic lesions
• Hypercalcemia develops from combination of increased osteoclastic resorption and increased tubular reabsorption of calcium mediated by PTHrP production

• Age: Incidence increases exponentially with age; median age at diagnosis 70 years; rare before age 40
• Race/Ethnicity: African Americans have 2-3 fold higher incidence than Caucasians; genetic and socioeconomic factors implicated
• Male gender: Male-to-female ratio approximately 1.4:1
• MGUS and Smoldering Myeloma: Precursor conditions with progression rates of 1% and 10% annually, respectively; represent obligate predecessors to MM
• Chronic antigenic stimulation: Chronic infections (HIV, hepatitis C), chronic inflammation, autoimmune diseases
• Environmental exposures: Radiation exposure (atomic bomb survivors, radiation workers) shows increased risk in some studies
• Chemical exposures: Benzene and pesticide exposure associated with increased risk in occupational cohorts
• Genetic predisposition: Familial clustering occurs; carriers of specific HLA alleles show increased susceptibility
• Obesity and metabolic factors: Some epidemiological associations identified but causality uncertain
• Prior malignancy: Secondary myeloma can develop following chemotherapy or radiation for other cancers (typically latency >5 years)

Cardinal Symptoms

• Bone pain (most common symptom, 70% of patients): Typically involves spine, ribs, pelvis; often sudden onset indicating pathological fracture; results from osteolytic lesions, periosteal irritation, and microfractures
• Fatigue and weakness: Directly correlates with severity of anemia; also attributable to metabolic derangements, renal dysfunction, and disease burden
• Recurrent infections: Due to immunoparesis (suppressed normal immunoglobulin), neutropenia, and hypogammaglobulinemia; bacterial infections predominate (especially Streptococcus pneumoniae, Haemophilus influenzae)
• Symptoms of hypercalcemia: Polyuria, polydipsia, constipation, confusion, lethargy; occurs in 10-15% at presentation, more common at progression
• Renal dysfunction symptoms: Polyuria, nocturia, progressive azotemia from light chain nephropathy
• Neurological symptoms: Radiculopathy from vertebral involvement; spinal cord compression from epidural tumor extension or collapse; peripheral neuropathy from light chains or amyloidosis

Physical Examination Findings

• Pallor: Manifestation of anemia; typically absent at presentation unless severe
• Bone tenderness: Localized pain over affected skeletal sites, particularly spine and ribs
• Splenomegaly (20%): Indicates advanced disease or extramedullary involvement
• Hepatomegaly (10%): Less common than splenomegaly; suggests extramedullary disease
• Lymphadenopathy: Unusual; if present, suggests transformation or secondary pathology
• Signs of hyperviscosity: Retinal hemorrhages, blurred vision, neurological symptoms (slurred speech, confusion, headache)
• Skin manifestations: Occasionally plasmacytomas presenting as nodular skin lesions

Laboratory Abnormalities

• Elevated creatinine and BUN: Light chain nephropathy; prerenal component from hypercalcemia and dehydration
• Elevated calcium: Due to osteoclast-mediated resorption; severity correlates with tumor burden
• Anemia (75%): Usually moderate (hemoglobin 8-10 g/dL); multifactorial etiology including marrow replacement, chronic disease, bleeding
• Elevated LDH: Marker of high tumor burden and aggressive disease; prognostic significance
• Hyperviscosity with IgA or IgM: Can cause clinical symptoms in 5-10% of cases
• Hypoalbuminemia: Reflects hepatic synthetic dysfunction and marrow replacement
• Rouleaux formation on blood smear: Characteristic RBC stacking from elevated immunoglobulin
• Normal or low WBC: Marrow infiltration suppresses normal hematopoiesis; infection risk increases with advanced disease

Specific Laboratory Tests for M-Protein

• Serum protein electrophoresis (SPEP): Demonstrates monoclonal spike (M-spike) in 80% of cases; absent in light chain disease
• Immunofixation electrophoresis (IFE): Identifies heavy and light chain type; more sensitive for small M-proteins
• Serum free light chain (FLC) assay: Abnormal FLC ratio highly sensitive; critical in light chain myeloma; prognostically significant
• 24-hour urine protein electrophoresis (UPEP): Detects Bence Jones protein (light chains); present in 50-80% of cases
• Beta-2 microglobulin: Elevated levels (>2.5 mg/L) indicate high tumor burden; prognostic significance in staging
• Albumin: Low albumin (≤3.5 g/dL) in RISS staging indicates worse prognosis

Bone Marrow Examination (Histology and Morphology)

• Bone marrow aspirate and trephine biopsy: Shows sheets or interstitial infiltration of abnormal plasma cells replacing normal marrow elements
• Morphologic findings of neoplastic plasma cells:
• Increased cytoplasm with abundant rough endoplasmic reticulum (producing immunoglobulin)
• Eccentric nuclei (cartwheel or clock-face appearance)
• Prominent nucleoli indicating high protein synthesis
• Increased mitotic activity in aggressive subtypes
• Plasmacytosis: Abnormal plasma cells >10% diagnostic for symptomatic MM; 5-10% in smoldering disease
• Immunohistochemistry: Malignant cells show monotypic light chain restriction (either kappa or lambda) with surface immunoglobulin; CD38+, CD138+, CD19+/-, CD20-
• Cytogenetic and FISH analysis: Identifies prognostically significant abnormalities (t(4;14), t(14;16), t(14;20), del(17p), del(13q), hyperdiploidy)
• Flow cytometry: Abnormal plasma cell population with aberrant phenotype; increased plasma cells with monotypic surface immunoglobulin

Diagnostic Criteria for Multiple Myeloma (IMWG 2014)

Myeloma Defining Events (MDE)

1. 1.Clonal bone marrow plasma cells ≥60%
2. 2.Serum free light chain ratio ≥100 (involved/uninvolved)
3. 3.>1 focal lesion on MRI of bone marrow

CRAB Criteria (End-Organ Damage)

• Calcium elevation (serum calcium >11.5 mg/dL or 2.65 mmol/L above upper normal limit)
• Renal insufficiency (creatinine clearance <40 mL/min or serum creatinine >2 mg/dL)
• Anemia (hemoglobin <10 g/dL or >2 g/dL below lower normal limit)
• Bone lesions (≥1 osteolytic lesion on skeletal survey, CT, or PET-CT)

Imaging Findings

• Skeletal survey (X-rays): Shows characteristic "punched-out" lytic lesions (well-demarcated round areas of bone loss without sclerotic margins) in skull, ribs, spine, pelvis
• Bone lesions: Predominantly lytic (bone resorption without new bone formation), distinguishing MM from other malignancies
• Spine involvement: Vertebral body destruction, collapse, and pathological fractures; may show epidural soft tissue masses
• MRI: Superior sensitivity for detection of marrow involvement and spinal cord compression; shows focal lesions (areas of high tumor burden) and diffuse infiltration (poor prognostic factor)
• PET-CT: Increasingly used for prognostic stratification; high SUV correlates with aggressive disease
• CT: Useful for characterizing complex bone lesions and detecting extramedullary disease

Gross Pathology

• Bone marrow: Homogeneous tan-white discoloration reflecting massive plasma cell infiltration; normal yellow fatty marrow replaced
• Involved bones: Pale, chalky appearance with punched-out defects visible on cross-section
• Extramedullary plasmacytomas (if present): Tan-white firm masses, typically in soft tissues around spine

Laboratory Panel Summary

• Complete metabolic panel: Assess renal function, calcium, albumin
• Complete blood count: Evaluate anemia, leukopenia, thrombocytopenia
• Coagulation studies: Assess for acquired defects (particularly with light chain disease)
• SPEP/IFE/FLC assay: Characterize monoclonal protein
• LDH and beta-2 microglobulin: Prognostic markers
• Bone marrow biopsy with flow, FISH, cytogenetics

Initial Approach and Risk Stratification

• Assess transplant eligibility: Age, comorbidities, performance status determine candidacy for high-dose chemotherapy with autologous stem cell transplant (ASCT), which remains standard of care in eligible patients
• Determine disease risk: High-risk features (del(17p), t(4;14), t(14;16), ≥3 focal lesions on MRI, elevated LDH) guide intensity and choice of agents
• Manage complications immediately: Address hypercalcemia, renal failure, anemia, infection, bone disease before initiating systemic therapy

First-Line Treatment in Transplant-Eligible Patients

• Induction therapy (3-4 months prior to ASCT):
• Bortezomib (proteasome inhibitor) + lenalidomide (IMiD) + dexamethasone (VRd) is preferred standard
• Daratumumab (anti-CD38 monoclonal antibody) addition to VRd (DVRd) improves outcomes
• Alternative: Bortezomib + dexamethasone if lenalidomide contraindicated
• Rationale: Proteasome inhibitors disrupt NF-κB pathway and trigger apoptosis; IMiDs enhance immune function and have direct anti-myeloma activity
• Mobilization and stem cell harvest: Performed after completion of induction therapy
• High-dose chemotherapy: Single or tandem autologous stem cell transplant
• Melphalan 200 mg/m² is standard conditioning agent
• Tandem ASCT offers benefit in some high-risk populations and younger patients
• Post-transplant consolidation: Further chemotherapy or targeted therapy may be added based on response
• Maintenance therapy:
• Lenalidomide monotherapy improves progression-free and overall survival
• Bortezomib-based regimens alternative in high-risk disease
• Duration: Until progression or intolerance

First-Line Treatment in Transplant-Ineligible Patients

• Backbone therapy:
• VRd (bortezomib + lenalidomide + dexamethas

Disease-related emergencies

• Hypercalcemic crisis (emergency): RANKL-driven osteoclast resorption plus volume depletion; signaled by confusion, polyuria, shortened QT. Treat with aggressive isotonic saline, calcitonin for rapid effect, and an IV bisphosphonate (or denosumab if renal function is poor) alongside anti-myeloma therapy.
• Spinal cord compression (emergency): epidural plasmacytoma or vertebral collapse; signaled by new bilateral leg weakness, saddle anesthesia, or bladder dysfunction. Emergent whole-spine MRI plus IV corticosteroids, then radiation or surgical decompression.
• Hyperviscosity syndrome (emergency): high-molecular-weight paraprotein (IgM > IgA > IgG) raises serum viscosity; signaled by sausage-link retinal veins, blurred vision, mucosal bleeding, and obtundation. Plasmapheresis is the immediate intervention.
• Cast nephropathy / acute kidney injury (urgent): filtered free light chains precipitate with Tamm-Horsfall protein in distal tubules; signaled by rising creatinine with bland sediment and a dipstick-negative but UPEP-positive proteinuria. Hydration, correction of hypercalcemia, avoidance of NSAIDs, and prompt bortezomib-based therapy per IMWG renal recommendations.
• Infection: immunoparesis and neutropenia predispose to encapsulated organisms and are a leading cause of death; any fever with neutropenia is an emergency requiring empiric broad-spectrum antibiotics.

Other disease complications

• Pathologic fracture and vertebral compression: uncoupled remodeling; bone-modifying agents (zoledronic acid, pamidronate, or denosumab) are recommended for all patients with myeloma bone disease by ASCO/NCCN.
• AL amyloidosis: misfolded light chains deposit as beta-pleated sheets; signaled by nephrotic-range proteinuria, restrictive cardiomyopathy with low-voltage ECG, macroglossia, periorbital purpura, and acquired factor X deficiency.
• Plasma cell leukemia / extramedullary disease: aggressive terminal transformation with circulating plasma cells.

Treatment-related complications

• Bortezomib: painful distal sensory neuropathy and varicella-zoster reactivation—antiviral prophylaxis is standard.
• Lenalidomide/thalidomide: high venous thromboembolism risk (thromboprophylaxis required) plus teratogenicity managed under a REMS program; long-term use adds secondary primary malignancy risk.
• Carfilzomib: heart failure and hypertension.
• Daratumumab: binds CD38 on RBCs, causing a pan-reactive indirect antiglobulin test—notify the blood bank before transfusion; it can also masquerade as an IgG-kappa M-spike.
• High-dose melphalan: prolonged cytopenias, mucositis, later therapy-related MDS/AML.
• Bisphosphonates/denosumab: osteonecrosis of the jaw (dental evaluation first) and hypocalcemia.

• The classic stem: an older, often African American patient with progressive back pain, anemia, renal insufficiency, and hypercalcemia. Elevated total protein with low albumin (a wide gap between total protein and albumin) is the tip-off; an unexplained low anion gap points to a cationic IgG paraprotein.
• Best next step after suspicion: SPEP with serum immunofixation plus a serum free light chain assay, then bone marrow biopsy with FISH. Urine dipstick detects albumin only, so Bence Jones light chains are dipstick-negative—order UPEP with immunofixation, not a dipstick.
• Imaging distractor to avoid: a radionuclide bone scan is typically negative because myeloma lesions are purely osteolytic with suppressed osteoblasts. Use low-dose whole-body CT, PET-CT, or MRI rather than a bone scan.
• Back pain plus any new neurologic deficit = emergent MRI of the whole spine and corticosteroids for possible cord compression—do not wait for the skeletal survey.
• Amyloid AL association examiners love: periorbital purpura and macroglossia, with tissue Congo red staining showing apple-green birefringence under polarized light. Nephrotic syndrome plus low-voltage ECG in a patient with an M-protein is AL until proven otherwise.
• Waldenström macroglobulinemia is the standard distractor: IgM from lymphoplasmacytic lymphoma, MYD88 L265P, hyperviscosity and lymphadenopathy, but no lytic bone lesions and no hypercalcemia. Hyperviscosity is treated with plasmapheresis.
• MGUS versus myeloma: MGUS has <10% clonal plasma cells, an M-protein below the smoldering threshold, and no CRAB or myeloma-defining event; per IMWG, management is observation with serial monitoring, not chemotherapy. Progression risk is roughly 1% per year.
• Solitary plasmacytoma of bone is treated with definitive radiation therapy, not systemic induction—but a full marrow and imaging workup must first exclude occult multiple myeloma.
• Hypercalcemia sequence: isotonic saline first, then calcitonin for speed and a bisphosphonate for durability; treat the myeloma to fix the cause.