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M Band (Monoclonal Protein) - Differential Diagnosis Other Than Multiple Myeloma

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Full Classification (WHO-5 / Goldman-Cecil)

I. Premalignant Monoclonal Gammopathies (most common overall)

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II. Malignant Monoclonal Gammopathies

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III. Heavy Chain Diseases (HCDs)

• γ-HCD (Franklin disease) - may mimic lymphoma; palatal edema classic
• α-HCD (Seligmann disease) - most common HCD; malabsorption/diarrhea (Mediterranean lymphoma)
• μ-HCD - resembles CLL; splenomegaly; vacuolated plasma cells

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IV. Cryoglobulinemia

• Type I: Monoclonal Ig (usually IgM or IgG) from plasma cell disorder or Waldenstrom
• Type II (Mixed): Monoclonal IgM + polyclonal IgG - most often Hepatitis C associated
• Type III: Polyclonal - connective tissue diseases

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V. Immunoglobulin Light Chain (AL) Amyloidosis

• Accounts for ~10% of M-protein cases (chart above)
• Free light chains deposit as amyloid in heart, kidneys, liver, nerves
• Often IgG lambda or free lambda
• Distinguished from MM by organ involvement pattern and absence of CRAB criteria

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VI. Other B-cell Lymphoproliferative Disorders That May Produce M Protein

• Chronic Lymphocytic Leukemia (CLL) - small IgM or IgG M band in some cases
• Diffuse Large B-cell Lymphoma (DLBCL)
• Marginal zone lymphoma
• Mantle cell lymphoma
• Follicular lymphoma

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VII. Reactive/Secondary M Proteins (Transient or Persistent)

• Chronic infections: HIV, HCV (Hepatitis C), HBV, tuberculosis, leishmaniasis
• Autoimmune diseases: SLE, RA, Sjogren syndrome
• Liver disease: cirrhosis (beta-gamma bridging can mimic)
• Post organ transplant
• Immunosuppressive therapy

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Memory Aid: SPAM-WC

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TdT-negative, CD3+, CD7+ Lymphoid Malignancy: Differential Diagnosis

Why This Immunophenotype Matters

"Mature αβ T cells express CD2, CD3, CD5, CD7, and either CD4 or CD8. They are negative for TdT and CD1." - Henry's Clinical Diagnosis and Management

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The Core Differentials

1. T-Cell Prolymphocytic Leukemia (T-PLL) - TOP DIFFERENTIAL

• Harrison's Principles of Internal Medicine 22e; Henry's Clinical Diagnosis, p. 766

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2. T-Cell Large Granular Lymphocytic (LGL) Leukemia

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3. Adult T-Cell Leukemia/Lymphoma (ATLL)

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4. Peripheral T-Cell Lymphoma, NOS (PTCL-NOS)

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5. Hepatosplenic T-Cell Lymphoma (HSTL)

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6. Enteropathy-Associated T-Cell Lymphoma (EATL)

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7. Mycosis Fungoides / Sézary Syndrome

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8. Aggressive NK-Cell Leukemia

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Summary Comparison Table

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Diagnostic Approach When TdT- CD3+ CD7+

1. First confirm: Is CD3 surface or cytoplasmic? (cytoplasmic only = NK-cell)
2. Add CD4, CD8, CD56, CD25, CD57, TCRαβ/γδ - narrow the T-cell subtype
3. Check CD7 intensity: CD7 bright = T-PLL; CD7 dim/lost = PTCL/ATLL/MF
4. HTLV-1 serology if CD4+, CD25+
5. EBV if clinical picture suggests NK/T-cell
6. TCR gene rearrangement to confirm clonality
7. Cytogenetics/FISH: inv(14) = T-PLL; isochromosome 7q = HSTL

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T-Cell (and NK-Cell) Neoplasms: Indolent vs. Aggressive

INDOLENT T-Cell Neoplasms

1. Mycosis Fungoides (MF) - Most Common CTCL

• 5-year survival: 88% (classic MF); Folliculotropic MF: 75%
• Epidermotropic CD4+ T-cell lymphoma; presents as patches → plaques → tumors
• Indolent course over years-decades; may transform to aggressive large-cell lymphoma
• Variants (all indolent):
  • Pagetoid reticulosis - 5-year OS ~100%
  • Granulomatous slack skin - 5-year OS ~100%

2. Lymphomatoid Papulosis (LyP)

• 5-year survival: 99% - most indolent T-cell disorder
• CD30+ self-regressing papulonodular skin lesions; wax and wane
• Despite histologic appearance of high-grade lymphoma, it is clinically benign
• ~10-20% develop secondary lymphoma (MF, ALCL, Hodgkin)

3. Primary Cutaneous Anaplastic Large Cell Lymphoma (C-ALCL)

• 5-year survival: 95%
• CD30+ solitary/localized skin nodules or tumors; often self-regressing
• ALK-negative (unlike systemic ALCL); excellent prognosis when skin-limited
• Treat with radiation or surgery; chemo only if disseminated

4. T-Cell Large Granular Lymphocytic (LGL) Leukemia

• Indolent; median survival measured in years
• CD3+, CD8+, CD57+, TCRαβ; large granular lymphocytes with azurophilic granules
• Presents with chronic neutropenia, mild lymphocytosis, splenomegaly
• Strongly associated with rheumatoid arthritis (Felty syndrome overlap)
• Treatment: cyclosporine, low-dose methotrexate, cyclophosphamide

5. NK-Cell Chronic Lymphoproliferative Disorder (Indolent NK-LGL Leukemia)

• CD2+, CD56+; no clonal EBV (distinguishes from aggressive NK leukemia)
• Discovered incidentally; no fever, no hepatosplenomegaly, no pancytopenia
• Indolent; may not require treatment

6. Subcutaneous Panniculitis-Like T-Cell Lymphoma (SPTCL) - αβ type

• 5-year survival: ~87%; Indolent
• αβ TCR type = indolent; γδ TCR type = aggressive (now classified separately as PCGD-TCL)
• Subcutaneous nodules mimicking panniculitis; rimming of fat cells
• Responds well to immunosuppression (steroids, cyclosporine)
• Prognosis worsens if hemophagocytic syndrome (HPS) develops

7. Primary Cutaneous CD4+ Small/Medium T-Cell Lymphoproliferative Disorder

• 5-year survival: ~100%
• Usually solitary facial lesion; low risk of dissemination
• Often managed with local excision alone

8. Primary Cutaneous Acral CD8+ T-Cell Lymphoproliferative Disorder

• 5-year survival: 100% (provisional WHO-5 entity - now classed as lymphoproliferative disorder)
• Localized to acral skin; very indolent

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AGGRESSIVE T-Cell Neoplasms

1. T-Cell Prolymphocytic Leukemia (T-PLL)

• Median survival: ~12 months - one of the most aggressive T-cell leukemias
• CD2+, CD3+ (weak), CD7++ (bright), CD4+ (60%), TdT-negative
• WBC often >100,000/μL; hepatosplenomegaly, skin involvement
• Cytogenetics: inv(14)(q11;q32) in 80%; trisomy 8q
• Treatment: alemtuzumab (anti-CD52) → allogeneic SCT in remission

2. Adult T-Cell Leukemia/Lymphoma (ATLL)

• Aggressive (acute) form: median survival months; chronic/smoldering forms are more indolent
• HTLV-1 driven; endemic in Japan, Caribbean, Central Africa
• CD3+, CD4+, CD25+ (IL-2 receptor), floret/cloverleaf cells
• Hypercalcemia, lytic lesions, skin involvement, lymphadenopathy
• 4 clinical forms: Acute (most common, most aggressive), Lymphomatous, Chronic (indolent), Smoldering (most indolent)

3. Extranodal NK/T-Cell Lymphoma, Nasal Type

• 5-year survival: 16% overall; as low as 7% with multiple risk factors
• EBV-driven; CD2+, CD56+, cytoplasmic CD3+ (surface CD3-)
• Angioinvasive, angiodestructive; "lethal midline granuloma"
• Common in Asia, Mexico, Central/South America
• Risk factors for poor prognosis: B symptoms, advanced stage, elevated LDH, regional LN involvement
• 5-year OS: 81% (0 risk factors) → 7% (3-4 risk factors)

4. Hepatosplenic T-Cell Lymphoma (HSTL)

• Poor prognosis; median OS ~16 months
• TCRγδ (usually); CD3+, CD7+, CD56+, CD4-, CD8-
• Young adults/adolescents; immunosuppressed (post-transplant, IBD on azathioprine/infliximab)
• Massive hepatosplenomegaly without lymphadenopathy; cytopenias
• Sinusoidal infiltration of liver, spleen, BM
• Isochromosome 7q in most cases

5. Enteropathy-Associated T-Cell Lymphoma (EATL)

• Median survival 7-11 months; very poor prognosis
• Associated with celiac disease (Type I = classic EATL)
• Type II (now: Monomorphic Epitheliotropic Intestinal T-Cell Lymphoma / MEITL) - not celiac-related; worse prognosis
• Presents with abdominal pain, perforation, malabsorption
• CD3+, CD7+, CD103+, CD8+; TIA-1+

6. Peripheral T-Cell Lymphoma, NOS (PTCL-NOS)

• 5-year survival: 15-30%; aggressive
• Diagnosis of exclusion after ruling out specific subtypes
• CD3+, usually CD4+; loss of CD5/CD7 = worse prognosis
• B symptoms, generalized lymphadenopathy, advanced stage at presentation
• Treatment: CHOP or CHOEP; brentuximab-CHP if CD30+

7. Angioimmunoblastic T-Cell Lymphoma (AITL) / Nodal TFH Lymphoma

• Median OS: 15-36 months; aggressive
• CD4+ TFH-derived: CD3+, CD10+, CXCL13+, PD-1+, BCL6+
• Systemic disease: fever, rash, polyarthritis, hemolytic anemia, polyclonal hypergammaglobulinemia
• EBV+ immunoblasts (risk of secondary EBV+ B-cell lymphoma)
• Mutations: TET2 (76%), DNMT3 (33%), IDH2 (20%)

8. Anaplastic Large Cell Lymphoma (ALCL)

• Two distinct entities with different prognosis:

• "Hallmark cells": horseshoe-shaped nuclei, prominent nucleoli; CD30++ (all types)
• Treatment: CHOP/CHOEP; Brentuximab vedotin (anti-CD30) for relapsed; crizotinib for relapsed ALK+ ALCL

9. Aggressive NK-Cell Leukemia

• Rapidly progressive; median survival weeks-months
• CD2+, CD56+, cytoplasmic CD3+; clonal EBV+
• Young Asians; fever, pancytopenia, hepatosplenomegaly, HPS, multiorgan failure
• del(6), del(17); serum Fas ligand elevated

10. Primary Cutaneous Gamma/Delta T-Cell Lymphoma (PCGD-TCL)

• 5-year survival: 11% - one of the most aggressive CTCLs
• TCRγδ; CD3+, CD56+, cytotoxic markers; CD4-, CD8-
• Disseminated skin lesions with mucosal/visceral involvement
• Formerly confused with SPTCL (now separated)

11. Primary Cutaneous Aggressive Epidermotropic CD8+ Cytotoxic T-Cell Lymphoma

• 5-year survival: 31% - aggressive
• Widespread skin lesions with epidermotropism; may disseminate to viscera
• CD8+, TIA-1+, granzyme B+; CD4-

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Summary Table

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B-Cell Neoplasms: Indolent vs. Aggressive

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INDOLENT B-Cell Neoplasms

1. Chronic Lymphocytic Leukemia / Small Lymphocytic Lymphoma (CLL/SLL) - Most Common Adult Leukemia

• Course: Indolent; median survival 7-10+ years (highly variable by stage)
• Immunophenotype: CD5+, CD19+, CD20 (dim), CD23+, CD10-, cyclin D1-; surface Ig dim
• Genetics: del(13q) = best prognosis; del(11q), del(17p)/TP53 = poor prognosis
• Mutation: IGHV mutated = better prognosis; IGHV unmutated = worse
• Key point: CLL (leukemic) and SLL (nodal) are the same disease; Richter transformation to DLBCL = aggressive conversion (~5-10%)
• Treatment (when needed): BTK inhibitors (ibrutinib, acalabrutinib), BCL-2 inhibitor (venetoclax), anti-CD20 (rituximab/obinutuzumab)
• Cytogenetics: del(13q14) most common; trisomy 12; del(11q); del(17p) - worst

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2. Follicular Lymphoma (FL) - Most Common Indolent Lymphoma

• Course: Indolent; median survival 8-15 years; Grade 1-2 = indolent; Grade 3B = aggressive (treat like DLBCL)
• Immunophenotype: CD10+, CD19+, CD20+, BCL2+, BCL6+, CD5-, CD23-
• Genetics: t(14;18) BCL2/IgH - hallmark translocation (85-90%); BCL2 overexpression prevents apoptosis
• Key features: Follicular architecture; "watch and wait" often appropriate for asymptomatic low-burden disease
• Transformation: ~30% transform to DLBCL over lifetime (histologic transformation = poor prognosis)
• Treatment: Rituximab ± chemotherapy (R-CHOP, R-bendamustine); lenalidomide; PI3K inhibitors for relapsed

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3. Marginal Zone Lymphomas (MZL) - Three Subtypes, All Indolent

• Immunophenotype (all): CD19+, CD20+, CD5-, CD10-, CD23-, BCL2+, surface Ig bright

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4. Hairy Cell Leukemia (HCL)

• Course: Indolent; very good prognosis with treatment (CR rates ~90%)
• Immunophenotype: CD19+, CD20+ (bright), CD11c+, CD25+, CD103+, CD123+, CD200+, Annexin A1+ (specific marker); cyclin D1+ (weak)
• Genetics: BRAF V600E mutation in ~100% of classic HCL (absent in HCL-variant and other B-cell LPDs)
• Morphology: "Hairy" cytoplasmic projections; TRAP (tartrate-resistant acid phosphatase) positive
• Presentation: Pancytopenia, massive splenomegaly, monocytopenia, "dry tap" on BM biopsy
• Treatment: Purine analogues (cladribine, pentostatin) = highly effective; BRAF inhibitor (vemurafenib) for refractory cases

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5. Lymphoplasmacytic Lymphoma (LPL) / Waldenstrom Macroglobulinemia (WM)

• Course: Indolent; median survival 5-10 years
• Hallmark: IgM monoclonal protein + hyperviscosity syndrome (headache, visual changes, bleeding, Raynaud's)
• Mutation: MYD88 L265P mutation in ~90% - key diagnostic mutation; CXCR4 mutations in ~30%
• Immunophenotype: CD19+, CD20+, CD25+, CD138 (plasma cell component), surface IgM+, CD5-, CD10-
• Key features: Lymphoplasmacytic morphology; BM infiltration; hyperviscosity requires urgent plasmapheresis
• Treatment: BTK inhibitors (ibrutinib), rituximab ± chemotherapy; plasmapheresis for hyperviscosity

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6. Splenic Diffuse Red Pulp Small B-Cell Lymphoma

• Course: Indolent; rare entity
• Often BRAF V600E negative (distinguishes from HCL); villous lymphocytes

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7. Nodular Lymphocyte-Predominant Hodgkin Lymphoma (NLPHL) (B-cell origin)

• Course: Indolent; excellent prognosis (>90% 10-year OS)
• CD20+, CD45+, CD79a+; CD15-, CD30- (distinguishes from classic HL)
• "Popcorn cells" / LP cells; CD4+ T-cell rosetting
• ~5% transform to DLBCL (usually LP cell transformation)

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8. Primary Cutaneous Marginal Zone Lymphoma

• 5-year OS: ~99% - extremely indolent
• Skin-limited; rarely disseminates
• Associated with Borrelia burgdorferi in some European cases

9. Primary Cutaneous Follicle Centre Lymphoma

• 5-year OS: ~95% - indolent
• CD10+, BCL6+, BCL2 usually negative (unlike nodal FL)
• Localized skin lesions; radiation often curative

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AGGRESSIVE B-Cell Neoplasms

1. Diffuse Large B-Cell Lymphoma (DLBCL) - Most Common Aggressive Lymphoma

• Course: Aggressive; but ~60-70% curable with R-CHOP
• Immunophenotype: CD19+, CD20+, CD79a+; variable CD10, BCL6, IRF4/MUM1
• Molecular subtypes (cell of origin):
  • GCB (Germinal Center B-cell): CD10+, BCL6+; t(14;18) BCL2; better prognosis
  • ABC/Non-GCB (Activated B-cell): IRF4/MUM1+; NF-κB activation; CARD11, MYD88 mutations; worse prognosis
• Special subtypes:
  • Double-hit (DHL): MYC + BCL2 rearrangements - very aggressive
  • Triple-hit (THL): MYC + BCL2 + BCL6 - worst prognosis
  • Double-expressor: Overexpression of MYC + BCL2 protein (without rearrangement)
  • Primary DLBCL of CNS: CD10-, BCL6+, MUM1+; treated with HD-MTX-based regimens
  • Primary mediastinal (thymic) large B-cell lymphoma (PMBCL): young women; CD30+, CD23+; distinct from DLBCL
  • EBV+ DLBCL: Older patients; aggressive
  • Primary testicular DLBCL: High CNS relapse risk; requires CNS prophylaxis
• Treatment: R-CHOP; CAR-T (axicabtagene, tisagenlecleucel) for relapsed/refractory

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2. Mantle Cell Lymphoma (MCL)

• Course: Aggressive but generally incurable; median survival 3-7 years
• The exception: Indolent/leukemic non-nodal MCL = truly indolent subset (SOX11-negative)
• Hallmark: t(11;14) BCL1/IgH → cyclin D1 overexpression (virtually diagnostic)
• Immunophenotype: CD5+, CD19+, CD20+, cyclin D1+, SOX11+, CD10-, CD23-
• "Blastoid variant" = most aggressive form
• High risk for GI involvement (lymphomatous polyposis)
• Treatment: Aggressive regimens (R-CHOP/R-DHAP alternating); BTK inhibitors (ibrutinib) for relapsed; auto-SCT consolidation

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3. Burkitt Lymphoma (BL)

• Course: Extremely aggressive; but highly curable with intensive chemotherapy (~80-90% cure in children)
• The fastest-growing human tumor - doubling time ~24-48 hours; Ki-67 ~100%
• Genetics: t(8;14) MYC/IgH (80%); t(2;8) or t(8;22) - ALL involve MYC
• Immunophenotype: CD10+, CD19+, CD20+, BCL6+, BCL2- (key!), TdT-, Ki-67 ~100%
• 3 clinical variants:
  • Endemic (African): EBV-driven; jaw/facial bones; children
  • Sporadic: Ileocecal mass; abdominal; children/young adults; EBV in ~30%
  • Immunodeficiency-associated: HIV; EBV in ~40%
• "Starry sky" appearance on histology (macrophages ingesting apoptotic tumor cells)
• Treatment: Intensive short-duration chemotherapy (R-CODOX-M/IVAC, R-hyperCVAD); tumor lysis syndrome prophylaxis mandatory

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4. High-Grade B-Cell Lymphoma with MYC and BCL2/BCL6 Rearrangements (Double/Triple Hit)

• Course: Very aggressive; 2-year OS ~30-50%
• Formally separated from DLBCL in WHO classification
• Often presents as de novo or as transformation of FL
• Treatment: More intensive than R-CHOP required (DA-EPOCH-R preferred); early auto-SCT

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5. Primary Mediastinal (Thymic) Large B-Cell Lymphoma (PMBCL)

• Course: Aggressive but potentially curable (~80% long-term survival)
• Young women; bulky anterior mediastinal mass; SVC syndrome
• CD30+, CD23+, MHC class II loss; CD10-, surface Ig-
• Genetically similar to nodular sclerosis Hodgkin lymphoma
• Treatment: DA-EPOCH-R (dose-adjusted); avoids routine radiation if PET-negative at end of therapy

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6. Plasmablastic Lymphoma

• Course: Very aggressive; poor prognosis (median OS ~15 months)
• Associated with HIV/immunosuppression; EBV+
• Plasma cell differentiation: CD138+, CD38+, MUM1+; CD20- (loses B-cell markers)
• High MYC expression; Ki-67 very high
• Involves jaw, oral cavity, GI tract

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7. Primary Effusion Lymphoma (PEL)

• Course: Very aggressive; median OS ~6 months
• HHV-8 (KSHV) driven; EBV co-infection common
• HIV/immunosuppressed patients
• Presents as lymphomatous effusion (pleural, pericardial, peritoneal) WITHOUT a tumor mass
• CD19-, CD20- (loses B-cell markers); CD138+, CD38+, HHV-8+

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8. Intravascular Large B-Cell Lymphoma

• Course: Aggressive; often fatal if unrecognized
• Tumor cells confined to lumens of small vessels; no tumor mass
• Presents with CNS/neurological symptoms, skin lesions, fever, cytopenias
• Random skin biopsy may be diagnostic

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9. CNS B-Cell Lymphoma (Primary CNS Lymphoma - PCNSL)

• Course: Aggressive; median OS 2-5 years with treatment
• Almost always DLBCL histology; CD10-, BCL6+, MUM1+ (ABC subtype)
• Periventricular lesions; steroid "melting sign"
• Treatment: High-dose methotrexate-based regimens; avoid whole-brain radiation if possible (neurotoxicity)

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Summary Classification Table

INDOLENT

AGGRESSIVE

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Important "Middle Ground" - Context-Dependent Behavior

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