Waldenström Macroglobulinemia (WM): Clinical, Pathobiology,
Diagnosis
Waldenström Macroglobulinemia คือ:
lymphoplasmacytic lymphoma (LPL) ที่มี IgM
monoclonal gammopathy
สำคัญ:
- เป็น B-cell neoplasm
- ไม่ใช่ classic plasma cell myeloma
- มีทั้ง lymphocyte + plasmacytoid cell + plasma cell
features
Core concept ของ WM
WM มี pathology 2 ส่วนหลัก
1. Tumor infiltration
โดย malignant lymphoplasmacytic cells
ทำให้:
- anemia
- lymphadenopathy
- hepatosplenomegaly
- marrow
failure
2. IgM-mediated disease
IgM monoclonal protein ทำให้:
- hyperviscosity
- neuropathy
- cryoglobulinemia
- cold
agglutinin disease
- organ
deposition
Epidemiology
- rare
disease
- incidence
~3/million/year
- median
age ~70 ปี
- male
predominance
- White
> Black populations
Familial predisposition:
- first-degree
relatives risk สูงขึ้น
Pathobiology แบบเข้าใจง่าย
Cell of origin
เชื่อว่าเกิดจาก:
post-germinal center IgM memory B cell
ที่:
- undergo
somatic hypermutation
- แต่ “ไม่ class-switch”
ดังนั้น:
- ยังสร้าง IgM อยู่
Major mutation
MYD88 L265P
สำคัญที่สุด
พบ:
90% ของ WM
Mechanism:
- activate
NF-kB pathway
- promote
survival signaling
Clinical pearl:
- strongly
supports WM diagnosis
- แต่ไม่ specific 100%
CXCR4 mutation
พบ ~40%
Associated with:
- biologic
heterogeneity
- altered
treatment response
Pathogenic mechanisms ของ IgM
1. Hyperviscosity
IgM เป็น pentamer
ขนาดใหญ่มาก
→ serum
viscosity เพิ่มง่าย
ทำให้:
- sluggish
blood flow
- capillary
dysfunction
2. Autoantibody activity
IgM อาจ attack:
- myelin-associated
glycoprotein (MAG)
→ neuropathy
หรือ:
- RBC
antigens
→ cold agglutinin hemolysis
3. Tissue deposition
IgM/amyloid deposit:
- kidney
- GI
tract
- skin
- nerve
4. Cryoglobulin formation
IgM precipitates in cold temperature
→
vasculitic/ischemic symptoms
Clinical presentation
Common symptoms
|
Manifestation |
Frequency |
|
Weakness/fatigue |
common |
|
Hyperviscosity symptoms |
~31% |
|
Bleeding |
~23% |
|
Neurologic symptoms |
~22% |
|
B symptoms |
~23% |
Important clinical pearl
ประมาณ 25%:
asymptomatic at diagnosis
Hyperviscosity syndrome
Classic hallmark ของ WM
Symptoms
Neurologic:
- headache
- dizziness
- blurred
vision
- tinnitus
- ataxia
- confusion
Bleeding:
- epistaxis
- gum
bleeding
Cardiac:
- heart
failure
Severe:
- coma/stroke
Fundoscopy classic finding
“sausage-link retinal veins”
เกิดจาก venous engorgement
Important thresholds
Symptoms rare if:
- viscosity
<4 cP
Most symptomatic:
- 6 cP
IgM >6000 mg/dL:
→ high risk hyperviscosity
Clinical pearl
Symptomatic hyperviscosity = medical emergency
Treatment:
- plasmapheresis
immediately
Neuropathy
พบ ~20%
Typical pattern:
- distal
symmetric sensory neuropathy
- lower
extremity predominant
- slowly
progressive
Mechanism
Often:
anti-MAG antibody mediated
Differential neuropathy pattern
|
Disease |
Pattern |
|
WM/MGUS |
demyelinating |
|
Amyloid |
axonal |
|
POEMS |
motor-predominant demyelinating |
Bing-Neel syndrome
Rare CNS infiltration by WM cells
Symptoms:
- cranial
neuropathy
- focal
deficits
- altered
mental status
Workup:
- MRI
brain/spine
- CSF
analysis
Poor prognosis
Cryoglobulinemia
IgM precipitates in cold
Symptoms:
- Raynaud
- purpura
- urticaria
- acral
ischemia
Kidney involvement
Rare (~3%)
Unlike MM:
- severe
renal failure less common
Mechanisms:
- IgM
deposition
- amyloid
- cryoglobulinemia
- infiltration
Important pearl
Light chain cast nephropathy:
- much
less common than MM
GI involvement
Rare
Mechanisms:
- IgM
deposition
- amyloid
- lymphatic
obstruction
Symptoms:
- malabsorption
- diarrhea
- protein-losing
enteropathy
Bone lesions
Important distinction from MM
WM:
- osteolytic
lesions rare
MM:
- lytic
lesions common
If:
- IgM
monoclonal protein + lytic lesions
→ think:
IgM myeloma
especially if:
- t(11;14)
CBC findings
Anemia
Common (~40%)
Mechanisms:
- marrow
infiltration
- inflammation/hepcidin
- iron
deficiency
- hyperviscosity
plasma expansion
- hemolysis
Peripheral smear
Classic:
- marked
rouleaux formation
Thrombocytopenia/leukopenia
Usually mild
Mechanisms:
- marrow
infiltration
- hypersplenism
- immune
destruction
Bleeding tendency
เกิดจาก:
- hyperviscosity
- platelet
dysfunction
- clotting
interference
Coagulation abnormalities
Common:
- prolonged
thrombin time
Mechanism:
IgM interferes fibrin polymerization
Bone marrow findings
Essential for diagnosis
Marrow:
- hypercellular
- lymphoplasmacytic
infiltrate
Classic:
- Dutcher
bodies
Immunophenotype
Typical WM:
|
Marker |
Expression |
|
CD19 |
+ |
|
CD20 |
+ |
|
CD22 |
+ |
|
CD25 |
+ |
|
CD5 |
usually - |
|
CD10 |
- |
|
CD23 |
- |
|
CD138 |
plasma cell component |
SPEP findings
Classic:
- monoclonal
IgM spike
Need:
- immunofixation
confirmation
Serum viscosity testing
Indications:
- hyperviscosity
symptoms
- IgM
>4 g/dL
Diagnostic criteria for WM
ต้องมีทั้งหมด:
1. Serum IgM monoclonal gammopathy
ทุกระดับได้
2. Bone marrow infiltration ≥10%
โดย:
- lymphoplasmacytic
lymphoma
3. Typical immunophenotype
Important pearl
MYD88 mutation:
- supports
diagnosis
- not
mandatory
Differential diagnosis
IgM MGUS
Criteria:
- IgM
<3 g/dL
- marrow
<10%
- asymptomatic
Progression:
~1.5%/year
Smoldering WM
Meets WM criteria แต่:
- asymptomatic
- no
organ damage
No treatment initially
IgM myeloma
Important distinction
Suggestive:
- lytic
lesions
- t(11;14)
- CD56+
- no
MYD88 mutation
Marginal zone lymphoma
More likely:
- bulky
lymphadenopathy
- splenomegaly
- extranodal
disease
CLL
Immunophenotype:
- CD5+
- CD23+
- FMC7-
Mantle cell lymphoma
Usually:
- cyclin
D1+
- t(11;14)
- CD5+
AL amyloidosis
Suggestive:
- nephrotic
syndrome
- cardiomyopathy
- macroglossia
- purpura
WM vs MM — high-yield comparison
|
Feature |
WM |
MM |
|
Cell origin |
lymphoplasmacytic B cell |
plasma cell |
|
M protein |
IgM |
IgG/IgA/light chain |
|
Bone lesion |
rare |
common |
|
Hyperviscosity |
common |
uncommon |
|
Neuropathy |
common |
less common |
|
MYD88 |
common |
absent |
|
t(11;14) |
absent |
common in IgM MM |
|
Renal failure |
less common |
common |
|
Hypercalcemia |
rare |
common |
High-yield take-home points
- WM =
LPL + IgM monoclonal gammopathy
- MYD88
L265P พบ >90%
- Hyperviscosity
syndrome เป็น hallmark
- IgM
causes disease via:
- hyperviscosity
- autoantibody
activity
- tissue
deposition
- cryoglobulinemia
- Neuropathy
มัก demyelinating
- Bone
lesions rare → ถ้ามีคิดถึง IgM MM
- Diagnosis
requires:
- IgM
monoclonal protein
- marrow
infiltration ≥10%
- LPL
phenotype
- Important
differential:
- IgM
MGUS
- IgM
myeloma
- marginal
zone lymphoma
- CLL
- mantle
cell lymphoma
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