In a patient with a 14‑month history of lymphocytosis, recent polychromasia, and five months of dizziness and vertigo, does the monoclonal B‑cell lymphocytosis (CD5‑positive, CD10‑negative, kappa‑restricted, absolute count ~2,600/µL) explain these symptoms, and what diagnostic work‑up and management steps are recommended?

The Monoclonal B-Cell Lymphocytosis Does Not Explain the Dizziness and Vertigo

Your patient's dizziness and vertigo are almost certainly unrelated to the monoclonal B-cell lymphocytosis (MBL) and require separate neurologic or vestibular evaluation. The MBL itself requires observation only, without treatment.

Why the MBL is Not Causing Symptoms

The flow cytometry confirms high-count MBL (absolute monoclonal B-cell count 2,626/µL, which is >0.5 × 10⁹/L but <5 × 10⁹/L) with a CLL-like immunophenotype (CD5+, CD10-, CD23 predominantly negative, kappa-restricted) 1, 2, 3. However, several critical points argue against MBL as the cause of her neurologic symptoms:

• Hyperviscosity does not occur in CLL/MBL: The guidelines explicitly state that "symptoms associated with leukocyte aggregates that develop in patients with acute leukemia rarely occur in patients with CLL" 1. Her absolute lymphocyte count (4,040/µL) and WBC (7,630/µL) are far too low to cause hyperviscosity syndrome.

• Constitutional symptoms are not part of MBL: By definition, MBL exists "in the absence of lymphadenopathy or organomegaly, cytopenias, or disease-related symptoms" 1. If significant symptoms were present, this would be CLL, not MBL.

• The polychromasia is mild: The +1 polychromasia likely represents a normal reticulocyte response or mild hemolysis, but there's no evidence of severe anemia (hemoglobin not provided but no mention of anemia in your presentation). This degree of polychromasia would not cause dizziness.

Atypical Immunophenotype Warrants Attention

The flow cytometry shows an unusual pattern that differs from typical CLL:

• CD23 predominantly negative (typical CLL is CD23+)
• Dim CD49d and FMC7 positive (FMC7 is typically negative in CLL)
• CD200 positive (helps distinguish from mantle cell lymphoma)

This immunophenotype raises the possibility of atypical CLL-like MBL rather than classic CLL-like MBL 3, 4. The CD5+/CD10-/CD23-negative pattern requires exclusion of mantle cell lymphoma, though the CD200 positivity argues against this diagnosis 2, 3.

Recommended Diagnostic Work-Up

For the MBL (Priority: Rule Out Mantle Cell Lymphoma)

1. FISH panel immediately: Specifically looking for t(11;14) to exclude mantle cell lymphoma, plus del(11q), del(13q), del(17p), and trisomy 12 for prognostic stratification 1, 3

2. Consider cyclin D1 testing if FISH unavailable or equivocal, given the atypical CD23-negative phenotype 3

3. Physical examination: Carefully assess for lymphadenopathy (nodes >1 cm) and splenomegaly (>6 cm below left costal margin). If present, this would be CLL or lymphoma, not MBL 1

4. No bone marrow biopsy needed: This is not indicated for MBL diagnosis or management 3

For the Dizziness/Vertigo (Separate Evaluation Required)

1. Complete metabolic panel and hemoglobin/hematocrit: Assess for anemia severity, electrolyte abnormalities, or renal dysfunction

2. Reticulocyte count and direct Coombs test: Evaluate the polychromasia - is this hemolysis or appropriate marrow response? 3

3. Serum protein electrophoresis (SPEP): Although hypergammaglobulinemia "does not by itself constitute a basis for initiating therapy" 1, paraproteinemia can occur and rarely cause hyperviscosity in other B-cell disorders

4. Neurologic/vestibular evaluation: The five-month duration of dizziness and vertigo requires dedicated assessment (MRI brain if central causes suspected, vestibular function testing if peripheral)

Management Algorithm

Immediate Actions

• Observation only for MBL 1, 2, 3. No treatment is indicated. Early treatment does not prolong survival and may increase risk of secondary malignancies 1

• Pursue alternative diagnosis for dizziness: This is the priority for symptom relief

Follow-Up Schedule for MBL

Every 3-6 months monitoring with:

• Physical examination (lymph nodes, liver, spleen)
• Complete blood count with differential
• Assessment for constitutional symptoms 5, 2

Criteria to Escalate from MBL to CLL Requiring Treatment

Treatment would only be indicated if she develops any of the following 1:

1. Progressive marrow failure: New or worsening anemia/thrombocytopenia
2. Massive splenomegaly: ≥6 cm below left costal margin, or progressive/symptomatic
3. Massive lymphadenopathy: ≥10 cm longest diameter, or progressive/symptomatic
4. Progressive lymphocytosis: >50% increase over 2 months OR lymphocyte doubling time <6 months (only if ALC >30 × 10⁹/L)
5. Autoimmune cytopenias: Poorly responsive to corticosteroids
6. Constitutional symptoms: ≥10% weight loss in 6 months, significant fatigue (ECOG PS ≥2), fevers >38°C for ≥2 weeks, or night sweats >1 month

Critical Pitfalls to Avoid

Do not treat based on lymphocyte count alone 1. The absolute lymphocyte count is not an indication for treatment in CLL/MBL.

Do not attribute all symptoms to MBL: This is an asymptomatic condition by definition. Her dizziness requires separate investigation.

Do not miss mantle cell lymphoma: The CD23-negative phenotype is atypical and mandates FISH for t(11;14) 3.

Monitor for infections and second malignancies: High-count MBL carries increased risk of both, even without progression to CLL 6, 4, 7. Ensure age-appropriate cancer screening and vaccinations are current.

Prognosis

High-count MBL progresses to CLL requiring treatment at approximately 1-2% per year 2, 3, 6, 7. The overall survival is similar to age-matched controls, though patients with higher-risk biologic features may have slightly reduced survival 7. The presence of atypical immunophenotype may alter this risk, pending FISH results.