Kahlers disease
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"multiple myeloma" AND treatment
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Kahler's Disease (Multiple Myeloma)
Kahler's disease is the eponymous name for multiple myeloma, named after the Austrian physician Otto Kahler who described the condition in 1889. It is a malignant neoplasm of plasma cells (terminally differentiated B lymphocytes) that accumulate in the bone marrow and produce a monoclonal immunoglobulin (M protein).
Epidemiology
- Approximately 30,000 new cases/year in the United States
- Median age at diagnosis: 70 years
- More common in males and in people of African descent (for unknown reasons)
- One of the most common lymphoid malignancies
Pathogenesis
Myeloma arises from a clonal expansion of malignant plasma cells. Key molecular events include:
- Chromosomal translocations fusing the IgH locus (chromosome 14) to oncogenes like cyclin D1 and cyclin D3, driving increased cell proliferation
- IL-6 from bone marrow stromal fibroblasts and macrophages supports myeloma cell proliferation
- Late-stage disease may show MYC translocations, particularly in aggressive cases
- Myeloma cells upregulate RANKL on stromal cells, activating osteoclasts and inhibiting osteoblasts - the net result is bone resorption
Pathophysiology - "CRAB" End-Organ Damage
The hallmark complications are summarized by the mnemonic CRAB:
| Letter | Complication | Mechanism |
|---|---|---|
| C | Hypercalcemia | RANKL-driven osteoclast activation + bone resorption |
| R | Renal failure | Bence Jones protein casts in distal tubules; light chain (AL) amyloid deposits; hypercalcemia-related |
| A | Anemia | Bone marrow replacement by plasma cells; normocytic normochromic type |
| B | Bone lesions | Lytic "punched-out" defects; pathologic fractures |
A myeloma-defining event also includes any of three biomarkers: clonal bone marrow plasma cells >60%, serum free light chain (FLC) ratio >100, or >1 focal lesion on MRI.
Immunoparesis is another major consequence - myeloma cells suppress normal B cell function. Despite elevated total immunoglobulin (from M protein), production of functional antibodies is depressed, putting patients at high risk for bacterial infections (a leading cause of death).
M Protein Profile
| Immunoglobulin Type | Frequency |
|---|---|
| IgG | 60% |
| IgA | 20-25% |
| Light chain only (Bence Jones) | ~20% |
| IgM, IgD, IgE | Rare |
| Non-secretory | ~1% |
Morphology & Imaging
Bone lesions:
- Multiple "punched-out" lytic defects, 1-4 cm in diameter, with no reactive sclerosis
- Most common sites: vertebral column, ribs, skull, pelvis, femur, clavicle, scapula
- Negative on bone scan (no reactive bone formation) - unlike metastatic carcinoma
- Pathologic fractures most common in vertebral column and femur
Bone marrow biopsy:
- Plasma cells >30% of cellularity (typically)
- Cells with "clock-face" chromatin, eccentric nucleus, perinuclear halo ("hof")
- Abnormal features: prominent nucleoli, Russell bodies (cytoplasmic immunoglobulin inclusions)
Myeloma kidney:
- Proteinaceous casts of Bence Jones proteins in distal tubules, surrounded by multinucleate giant cells
- Adjacent tubular epithelial necrosis/atrophy
- AL amyloid in glomeruli and vessel walls
Diagnostic Criteria (IMWG 2014)
Diagnosis of active multiple myeloma requires:
- Clonal bone marrow plasma cells ≥10% OR histologically proven plasmacytoma
- Plus either:
- Evidence of CRAB end-organ damage attributable to the plasma cell disorder, OR
- One of the myeloma-defining biomarkers (above)
Key laboratory tests:
- Serum protein electrophoresis (SPEP): tall, narrow-based M spike in gamma region
- Serum immunofixation to identify M protein type
- Serum free light chain assay: abnormal κ/λ ratio (normal 0.26-1.65)
- 24-hour urine for Bence Jones proteins
- Bone marrow biopsy
- Skeletal survey (X-ray) or whole-body low-dose CT/PET-CT
Staging
The Revised International Staging System (R-ISS) is based on:
- Serum β2-microglobulin and albumin levels
- Cytogenetic risk (e.g., del 17p, t(4;14), t(14;16) = high risk)
- LDH
Spectrum of Plasma Cell Disorders
| Entity | Plasma cells | M protein | End-organ damage |
|---|---|---|---|
| MGUS | <10% marrow | <3 g/dL | None |
| Smoldering myeloma | 10-59% marrow | ≥3 g/dL | None |
| Active myeloma | ≥10% OR any | Any | CRAB or biomarkers |
| Solitary plasmacytoma | Solitary lesion | Minimal | None elsewhere |
Treatment
Transplant-eligible patients (~50%)
- Induction (3-4 months): VRd (bortezomib + lenalidomide + dexamethasone) is the standard; adding daratumumab (DVRd) is considered in high-risk disease
- Stem cell collection (GCSF ± plerixafor)
- Autologous SCT: high-dose melphalan 200 mg/m² conditioning
- Maintenance: lenalidomide 10 mg/day (long-term); bortezomib added in high-risk disease
Transplant-ineligible patients
- DRd (daratumumab + lenalidomide + dexamethasone) or VRd at adjusted doses
- VCD (bortezomib + cyclophosphamide + dexamethasone) as alternative
Drug classes and mechanisms
| Drug Class | Agents | Mechanism |
|---|---|---|
| Proteasome inhibitors | Bortezomib, carfilzomib, ixazomib | Block 26S proteasome → NF-κB downregulation → apoptosis |
| IMiDs | Thalidomide, lenalidomide, pomalidomide | Immunomodulation, anti-angiogenesis, direct anti-myeloma effects |
| Anti-CD38 mAb | Daratumumab | Targets CD38 (highly expressed on myeloma cells) |
| Anti-SLAMF7 mAb | Elotuzumab | Targets SLAMF7 on myeloma cells |
| CAR-T therapy | Ide-cel (idecabtagene vicleucel) | Targets BCMA; used for relapsed/refractory after 4+ prior lines |
| Alkylating agents | Melphalan, cyclophosphamide | DNA cross-linking |
CAR-T note: Recent meta-analyses (2024) show significant activity for ide-cel and ciltacabtagene autoleucel in relapsed/refractory disease, but risks include cytokine release syndrome, neurotoxicity, and prolonged cytopenias. A 2024 meta-analysis comparing CAR-T vs bispecific antibodies in 3rd-line and beyond myeloma (PMID 39551604) is relevant for current practice decisions.
Prognosis
- Median overall survival: approximately 5 years with modern therapy
- Patients with multiple bone lesions, if untreated: rarely survive >6-12 months
- Smoldering myeloma may not require treatment for many years
- Multiple myeloma remains incurable with current therapy but remarkable progress has been made - Goldman-Cecil Medicine, 2024
Key Associations / Pearls
- Bence Jones proteins in urine = free light chains (not detected by standard urine dipstick)
- Rouleaux formation on peripheral blood smear due to elevated globulins
- Hyperviscosity syndrome (particularly with IgM) - blurred vision, bleeding, neurologic changes
- Amyloidosis (AL type) - certain light chains deposit as amyloid, worsening renal dysfunction
- Absence of M protein does NOT exclude diagnosis (1% nonsecretory myeloma)
- Unlike metastatic bone disease, myeloma lesions are cold on bone scan
Sources: Robbins & Kumar Basic Pathology, Goldman-Cecil Medicine, Katzung's Basic and Clinical Pharmacology 16e, Campbell's Operative Orthopaedics 15e
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