What conditions cause neutropenia with lymphocytosis?

Neutropenia with Lymphocytosis: Differential Diagnosis

The most important cause to consider when neutrophils are low and lymphocytes are high is Large Granular Lymphocyte (LGL) leukemia, a chronic lymphoproliferative disorder that characteristically presents with this specific pattern of cytopenias. 1

Primary Hematologic Causes

Large Granular Lymphocyte Leukemia (Most Common)

• LGL leukemia is characterized by clonal expansion of cytotoxic T-cells or NK cells with chronic neutropenia present in up to 80% of cases 1
• The lymphocytes are typically CD3+, CD8+, CD57+ with cytoplasmic azurophilic granules 2, 3
• Patients often present with moderate lymphocytosis, neutropenia (frequently <0.5 × 10⁹/L), splenomegaly without lymphadenopathy, and a chronic stable course 4
• STAT3 mutations are now recognized as relevant pathogenic features 1
• The neutropenia results from multiple mechanisms including humoral autoantibodies, bone marrow infiltration, and cell-mediated cytotoxicity 5, 6, 1
• Approximately 76% of T-cell expansions are clonal as demonstrated by molecular studies 2

Chronic Lymphocytic Leukemia (CLL)

• CLL commonly presents with lymphocytosis and varying degrees of cytopenias including neutropenia 7, 8
• Patients with CLL have compromised immune function related to both the disease and therapy 7
• The disease is characterized by clonal B-cell proliferation, though neutropenia may occur from marrow infiltration or autoimmune mechanisms 8

Felty's Syndrome

• The association of rheumatoid arthritis with idiopathic neutropenia and lymphocytosis, found in over 90% of cases with HLA-DR4 2
• Approximately 19-42% of Felty's syndrome patients have evidence of LGL expansions 2
• These patients may have CD3+CD8+CD57+ T-cell lymphocytosis overlapping with LGL syndrome 2

Secondary Causes

Medication-Induced

• Azathioprine and 6-mercaptopurine cause bone marrow toxicity leading to leukopenia in approximately 3% of patients 9
• Risk is highest in individuals with thiopurine-methyltransferase (TPMT) deficiency 9
• Mycophenolate mofetil commonly causes combined leukopenia and thrombocytopenia 9
• Ganciclovir and trimethoprim-sulfamethoxazole frequently induce leukopenia 9
• Isolated lymphopenia during azathioprine therapy may result from lymphocytotoxic effects; dose reduction is recommended if lymphocyte count falls below 0.5 × 10⁹/L 9

Infectious Causes

• Cytomegalovirus (CMV) infection in transplant recipients can present with concurrent anemia and leukopenia 9
• Viral infections (HSV, RSV, parainfluenza, influenza) may cause initial neutropenia in immunocompromised patients 10

Hypersplenism

• Hypersplenism leads to neutropenia through increased sequestration and peripheral destruction of white blood cells 9
• In cirrhotic patients, moderate leukopenia occurs in approximately 2.7% of non-neutropenic presentations 9

Chronic Inflammatory Conditions

• Persistent leukocytosis (which may include relative lymphocytosis with neutropenia) can occur with autoimmune diseases, chronic infections, and inflammatory bowel disease 11

Diagnostic Approach

Essential Laboratory Evaluation

• Complete blood count with differential to quantify absolute neutrophil and lymphocyte counts 10
• Peripheral blood smear examination for large granular lymphocytes with azurophilic granules 3
• Flow cytometry immunophenotyping: look for CD3+, CD8+, CD57+ phenotype characteristic of LGL 2, 3
• TCR gene rearrangement studies or TCR V-beta chain analysis to detect clonal T-cell populations 2
• STAT3 mutation testing in suspected LGL leukemia 1
• Bone marrow examination if diagnosis remains unclear 4

Additional Testing Based on Clinical Context

• Rheumatoid factor and anti-CCP antibodies if Felty's syndrome suspected 2
• TPMT genotyping if patient on thiopurine medications 9
• CMV PCR in transplant recipients 9
• Exclude concurrent hematologic malignancies through appropriate workup 9

Clinical Significance and Management Implications

Infection Risk Stratification

• Neutropenia severity correlates with infection risk: greatest when absolute neutrophil count <100/mcL 10
• Duration of neutropenia and rate of decline are critical prognostic factors 10
• Approximately 50-60% of febrile neutropenic patients have established or occult infection 10

Common Pitfalls

• Do not assume benign reactive lymphocytosis without excluding clonal LGL proliferation 4
• The finding of clonal chromosome abnormalities suggests neoplastic origin, though spontaneous regression can occur in some cases 4
• LGL leukemia may have a chronic stable course for years, but patients remain at risk for serious bacterial infections due to persistent neutropenia 4, 3
• Autoimmune mechanisms (anti-neutrophil antibodies) may contribute but are not the sole cause of neutropenia in LGL 5, 6