Leukopenia

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Chapter 125 Leukopenia

Marked developmental changes in normal values for the total white blood cell (WBC) count occur during childhood (Chapter 708). The mean WBC count at birth is high, followed by a rapid fall beginning at 12 hr until the end of the 1st wk. Thereafter, values are stable until 1 yr of age. A slow, steady decline in the WBC count continues throughout childhood until reaching the adult value during adolescence. Leukopenia in adolescents and adults is defined as a total WBC count <4,000/µL. Evaluation of patients with leukopenia, neutropenia, or lymphopenia begins with a thorough history, physical examination, family history, and screening laboratory tests (Table 125-1).

Table 125-1 DIAGNOSTIC APPROACH FOR PATIENTS WITH LEUKOPENIA

EVALUATION ASSOCIATED CLINICAL DIAGNOSES
INITIAL EVALUATION
• History of acute or chronic leukopenia  
• General medical history Congenital syndromes (Shwachman-Diamond, Wiskott-Aldrich, Fanconi anemia, dyskeratosis congenita, glycogen storage disease type Ib, disorders of vesicular transport)
• Physical examination: stomatitis, gingivitis, dental defects, congenital anomalies
• Spleen size Hypersplenism
• History of drug exposure Drug-associated neutropenia
• Complete blood count with differential and reticulocyte counts Neutropenia, aplastic anemia, autoimmune cytopenias
IF ANC <1,000/µL
EVALUATION OF ACUTE ONSET NEUTROPENIA
• Repeat blood counts in 3-4 weeks Transient myelosuppression (e.g., viral)
• Serology and cultures for infectious agents Active or chronic infection with viruses (e.g., EBV, CMV), bacteria, mycobacteria, rickettsia
• Discontinue drug(s) associated with neutropenia Drug-associated neutropenia
• Test for antineutrophil antibodies Autoimmune neutropenia
• Measure quantitative immunoglobulins (G, A, and M), lymphocyte subsets Neutropenia associated with disorders of immune function
IF ANC <500/µL ON 3 SEPARATE TESTS
• Bone marrow aspiration and biopsy, with cytogenetics Severe congenital neutropenia, Shwachman-Diamond syndrome, myelokathexis; chronic benign or idiopathic neutropenia
• Serial CBCs (3/week for 6 weeks) Cyclic neutropenia
• Exocrine pancreatic function Shwachman-Diamond syndrome
• Skeletal radiographs Shwachman-Diamond syndrome, cartilage-hair hypoplasia, Fanconi anemia
IF ABSOLUTE LYMPHOCYTE COUNT <1000/µL
• Repeat blood counts in 3-4 weeks Transient leukopenia (e.g., viral)
IF ALC <1000/µL ON 3 SEPARATE TESTS
• HIV-1 antibody test HIV-1 infection, AIDS
• Quantitative immunoglobulins (G, A, and M), lymphocyte subsets Congenital or acquired disorders of immune function
IF THERE IS PANCYTOPENIA
• Bone marrow aspiration and biopsy Bone marrow replacement by malignancy, fibrosis, granulomata, storage cells
• Bone marrow cytogenetics Myelodysplasia, leukemia
• Vitamin B12 and folate levels Vitamin deficiencies

ANC, absolute neutrophil count; CBC, complete blood count; CMV, cytomegalovirus; EBV, Epstein-Barr virus.

Neutropenia

Neutropenia is an absolute neutrophil count (ANC), calculated as the WBC count × % of neutrophils and bands, more than 2 standard deviations below the normal mean. Normal neutrophil counts must be stratified for age and race. For whites over the age of 12 mo, the lower limit of normal for the neutrophil count is 1,500/µL, and for blacks over 12 mo old, the lower limit of normal is 1,200/µL. The relatively lower limit in blacks probably reflects a relative decrease in neutrophils in the storage compartment of the bone marrow. Neutropenia may be characterized as mild neutropenia, with an ANC of 1,000-1,500/µL; moderate neutropenia, with an ANC of 500-1,000/µL; or severe neutropenia, with an ANC <500/µL. This stratification aids in predicting the risk of pyogenic infection; only patients with severe neutropenia have significantly increased susceptibility to life-threatening infections.

Etiology

Acute neutropenia evolving over a few days often occurs when neutrophil use is rapid and production is compromised. Chronic neutropenia lasting months or years can arise from reduced production, increased destruction, or excessive splenic sequestration of neutrophils. Neutropenia may be classified by whether it arises secondary to factors extrinsic to marrow myeloid cells (Table 125-2), which is common; as an acquired disorder of myeloid progenitor cells (Table 125-3), which is less common; or, more rarely, as an intrinsic defect affecting proliferation and maturation of myeloid progenitor cells (Table 125-4).

Table 125-2 CAUSES OF NEUTROPENIA EXTRINSIC TO MARROW MYELOID CELLS

CAUSE ETIOLOGIC FACTORS/AGENTS ASSOCIATED FINDINGS
Infection Viruses, bacteria, protozoa, rickettsia, fungi Redistribution from circulating to marginating pools, impaired production, accelerated destruction
Drug-induced Phenothiazines, sulfonamides, anticonvulsants, penicillins, aminopyrine Hypersensitivity reaction (fever, lymphadenopathy, rash, hepatitis, nephritis, pneumonitis, aplastic anemia), antineutrophil antibodies
Immune neutropenia Alloimmune, autoimmune Variable arrest from metamyelocyte to segmented neutrophils in bone marrow
Reticuloendothelial sequestration Hypersplenism Anemia, thrombocytopenia, neutropenia
Bone marrow replacement Malignancy (lymphoma, metastatic solid tumor, etc.) Presence of immature myeloid and erythroid precursors in peripheral blood
Cancer chemotherapy or radiation therapy to bone marrow Suppression of myeloid cell production Bone marrow hypoplasia, anemia, thrombocytosis

Table 125-3 ACQUIRED DISORDERS OF MYELOID CELLS

CAUSE ETIOLOGIC FACTORS/AGENTS ASSOCIATED FINDINGS
Aplastic anemia Stem cell destruction and depletion Pancytopenia
Vitamin B12 or folate deficiency Malnutrition; congenital deficiency of B12 absorption, transport, and storage; vitamin avoidance Megaloblastic anemia, hypersegmented neutrophils
Acute leukemia, chronic myelogenous leukemia Bone marrow replacement with malignant cells Pancytopenia, leukocytosis
Myelodysplasia Dysplastic maturation of stem cells Bone marrow hypoplasia with megaloblastoid red cell precursors, thrombocytopenia
Prematurity with birthweight <2 kg Impaired regulation of myeloid proliferation and reduced size of postmitotic pool Maternal preeclampsia
Chronic idiopathic neutropenia Impaired myeloid proliferation and/or maturation None
Paroxysmal nocturnal hemoglobinuria Acquired stem cell defect secondary to mutation of PIG-A gene Pancytopenia, thrombosis

Table 125-4 INTRINSIC DISORDERS OF MYELOID PRECURSOR CELLS

SYNDROME INHERITANCE (GENE) CLINICAL FEATURES (INCLUDING STATIC NEUTROPENIA UNLESS OTHERWISE NOTED)
PRIMARY DISORDERS OF MYELOPOIESIS
Cyclic neutropenia AD (ELA2) Periodic oscillation (21-day cycles) in ANC
Severe congenital neutropenia AD (ELA2, GFI1, others) Risk of MDS and AML
X-linked (WAS) Neutropenic variant of Wiskott-Aldrich syndrome
Kostmann syndrome AR (HAX1) Neurological abnormalities, risk of MDS and AML
DISORDERS OF RIBOSOMAL FUNCTION
Shwachman-Diamond syndrome AR (SBDS) Pancreatic insufficiency, variable neutropenia, other cytopenias, metaphysical dysostosis
Dyskeratosis congenita Telomerase defects: XL (DKC1), AD (TERC), AR (TERT) Nail dystrophy, leukoplakia, reticulated hyperpigmentation of the skin; 30-60% develop bone marrow failure
DISORDERS OF GRANULE SORTING
Chédiak-Higashi syndrome AR (LYST) Partial albinism, giant granules in myeloid cells, platelet storage pool defect, impaired natural killer cell function, hemophagocytic lymphohistiocytosis
Griscelli syndrome, type II AR (RAB27a) Partial albinism, impaired natural killer cell function, hemophagocytic lymphohistiocytosis
Cohen syndrome AR (COH1) Partial albinism
Hermansky-Pudlak syndrome, type II AR (AP3P1) Cyclic neutropenia, partial albinism
p14 deficiency probable AR (MAPBPIP) Partial albinism, decreased B and T cells
DISORDERS OF METABOLISM
Glycogen storage disease, type 1b AR (G6PT1) Hepatic enlargement, growth retardation, impaired neutrophil motility
G6Pase, catalytic subunit 3, deficiency AR (G6PC3) Structural heart defects, urogenital abnormalities, venous angiectasia
Barth syndrome XL (TAZ1) Episodic neutropenia, dilated cardiomyopathy, methylglutaconic aciduria
Pearson’s syndrome Mitochondrial (DNA deletions) Episodic neutropenia, pancytopenia; defects in exocrine pancreas, liver, and kidneys
NEUTROPENIA IN DISORDERS OF IMMUNE FUNCTION
Common variable immunodeficiency Familial, sporadic (TNFRSF13B) Hypogammaglobulinemia, other immune system defects
IgA deficiency Unknown (Unknown or TNFRSF13B) Decreased IgA
Severe combined immunodeficiency AR, XL (multiple loci) Absent humoral and cellular immune function
Hyper-IgM syndrome XL (HIGM1) Absent IgG, elevated IgM, autoimmune cytopenia
WHIM syndrome AD (CXCR4) Warts, hypogammaglobulinemia, infections, myelokathexis
Cartilage-hair hyperplasia AR (RMKP) Lymphopenia, short-limbed dwarfism, metaphysical chondrodysplasia, fine sparse hair
Schimke immuno-osseous dysplasia probable AR (SMARCAL1) Lymphopenia, pancytopenia, spondyloepiphyseal dysplasia, growth retardation, renal failure

AD, autosomal dominant; AML, acute myelogenous leukemia; ANC, absolute neutrophil count; AR, autosomal recessive; MDS, myelodysplasia; XL, X-linked.

Infectious Causes

Transient neutropenia often accompanies or follows viral infections (Table 125-5). Neutropenia associated with common childhood viral disease occurs during the 1st 1-2 days of illness and may persist for 3-8 days. It usually corresponds to a period of acute viremia and is related to virus-induced redistribution of neutrophils from the circulating to the marginating pool. Neutrophil sequestration possibly occurs after virus-induced tissue damage. Moderate to severe neutropenia may also be associated with a wide variety of other infectious causes. Bacterial sepsis is a particularly serious cause of neutropenia and neonates are particularly vulnerable to developing neutropenia because of a deficient pool of reserve neutrophils in the bone marrow.

Table 125-5 INFECTIONS THAT ARE ASSOCIATED WITH NEUTROPENIA

VIRAL

Respiratory syncytial virus

Dengue fever

Colorado tick fever

Mumps

Viral hepatitis

Infectious mononucleosis (Epstein-Barr virus)

Influenza

Measles

Rubella

Varicella

Cytomegalovirus

Human immunodeficiency virus

Sandfly fever

BACTERIAL

Pertussis

Typhoid fever

Paratyphoid fever

Tuberculosis (disseminated)

Brucellosis

Tularemia

Gram-negative sepsis

Psittacosis

FUNGAL

Histoplasmosis (disseminated)

PROTOZOA

Malaria

Leishmaniasis (kala-azar)

RICKETTISIAL

Rocky Mountain spotted fever

Typhus fever

Rickettsialpox

From Boxer LA, Blackwood RA: Leukocyte disorders: quantitative and qualitative disorders of the neutrophil, part 1, Pediatr Rev 17:19–28, 1996.

Chronic neutropenia often accompanies infection with Epstein-Barr virus, cytomegalovirus, or HIV. The neutropenia associated with AIDS probably arises from a combination of impaired neutrophil production, the accelerated destruction of neutrophils mediated by antineutrophil antibodies, and sometimes effects of antiretroviral or other drugs.

Drug-Induced Neutropenia

Drugs constitute one of the most common causes of neutropenia (Table 125-6). The incidence of drug-induced neutropenia increases dramatically with age; only 10% of cases occur among children and young adults, and the majority of cases among adults over age 65 yr. Drug-induced neutropenia has several underlying mechanisms (immune-mediated, toxic, idiosyncratic, hypersensitivity reactions) that are distinct from the severe neutropenia that predictably occurs after administration of cytoreductive cancer drugs or radiotherapy.

Drug-induced neutropenia due to immune mechanisms usually develops abruptly, is accompanied by fever, and lasts for about 1 wk after discontinuation of the drug. The process likely arises from effects of drugs such as propylthiouracil or penicillin that act as haptens to stimulate antibody formation, or drugs such as quinine that induce immune complex formation. Other drugs, including the antipsychotic drugs such as the phenothiazines, can cause neutropenia when given in toxic amounts, but some individuals, such as those with pre-existing neutropenia, may be susceptible to levels at the high end of the usual therapeutic range. Late-onset neutropenia can occur after rituximab therapy. Idiosyncratic reactions, for example to chloramphenicol, are unpredictable with regard to dose or duration of use. Hypersensitivity reactions are rare and may involve arene oxide metabolites of aromatic anticonvulsants. Fever, rash, lymphadenopathy, hepatitis, nephritis, pneumonitis, and aplastic anemia are often associated with hypersensitivity-induced neutropenia. Acute hypersensitivity reactions such as those caused by phenytoin or phenobarbital may last for only a few days if the offending drug is discontinued. Chronic hypersensitivity may last for months to years. Drug-induced neutropenia may occasionally be asymptomatic despite severely reduced numbers of neutrophils and is noted only because of regular monitoring of WBC counts during drug therapy.

Neutropenia commonly and predictably follows the use of anticancer drugs or radiation therapy, especially radiation therapy directed at the pelvis or vertebrae, secondary to cytotoxic effects on rapidly replicating myeloid precursors. A decline in the WBC count typically occurs 7-10 days after administration of the anticancer drug and may persist for 1-2 wk. The neutropenia accompanying malignancy or following cancer chemotherapy is frequently associated with compromised cellular immunity, thereby predisposing patients to a much greater risk of infection (Chapter 171) than found in disorders associated with isolated neutropenia.

Autoimmune Neutropenia of Infancy (ANI)

This benign condition is diagnosed more frequently as techniques for detection of antineutrophil antibodies have become more available. The exact incidence of ANI remains unknown, but because of its benign nature, the disorder may be more common than currently appreciated. In 1 study, ANI occurred with an annual incidence of approximately 1/100,000 among children between infancy and 10 yr. All patients recognized as having ANI have severe neutropenia on presentation, with an ANC usually <500/µL, but the total WBC count is generally within normal limits. Monocytosis or eosinophilia may occur but does not affect the low rate of infection. The age at diagnosis is usually between 5 and 15 mo, with a female to male ratio of 6:4. None of the affected children has evidence of other autoimmune diseases. Children with ANI present with minor infections such as otitis media, gingivitis, respiratory tract infections, gastroenteritis, and cellulitis. The diagnosis often is considered only after the blood count reveals neutropenia. Occasionally, children may present with more severe infections, including pneumonia, sepsis, or abscesses. Longitudinal studies of infants with ANI demonstrate a median duration of disease of ≈7-24 mo. The diagnosis is established by the presence of antineutrophil antibodies in serum.

Treatment is not generally necessary, but rhG-CSF may be useful in providing temporary remission in infants with severe infections or requiring surgical intervention.

Ineffective Myelopoiesis

Intrinsic Disorders of Myeloid Precursors

The isolated disorders of proliferation and maturation of myeloid precursor cells are rare. Table 125-4 presents a classification based on genetics and molecular mechanisms; selected disorders are discussed in the next sections.

Primary Disorders of Granulocytopoiesis

Cyclic neutropenia, an autosomal dominant disorder, is characterized by regular, periodic oscillation in the number of peripheral neutrophils from normal to neutropenic values with a mean oscillatory period of 21 ± 3 days. During the neutropenic phase, most patients suffer from fever, stomatitis or pharyngitis, and occasionally lymph node enlargement. Serious infections may occur at the ANC nadirs, including pneumonia, periodontitis, and recurrent ulcerations of the oral, vaginal, and rectal mucosa, leading to life-threatening clostridial sepsis. Cyclic neutropenia arises from a regulatory abnormality involving early hematopoietic precursor cells and is associated with mutations in the neutrophil elastase gene, ELA2, that lead to accelerated apoptosis due to abnormal protein folding. Many patients experience abatement of symptoms with age. The cycles tend to become less noticeable in older patients, and the hematologic picture often begins to resemble that of chronic neutropenia. Treatment with rhG-CSF elevates the neutrophil counts and improves outcome.

Severe congenital neutropenia is characterized by an arrest in myeloid maturation at the promyelocyte stage in the bone marrow, resulting in consistent ANCs <200/µL. This disorder occurs sporadically or with autosomal dominant or recessive inheritance. The dominant form is caused most often by mutations in ELA2, while the recessive form (Kostmann disease) arises from mutations in HAX1, which protects cells against apoptosis. Patients typically show monocytosis and eosinophilia and suffer from recurrent, severe pyogenic infections, especially of the skin, mouth, and rectum. Anemia of chronic inflammation is often present. Approximately 20% of patients develop acute myelogenous leukemia or myelodysplasia associated with monosomy 7 and sometimes preceded by acquisition of mutations in the gene encoding the G-CSF receptor. Before the advent of treatment with rhG-CSF, most of these patients died of fatal infections before reaching adolescence.

Neutropenia in Disorders of Immune Function

Congenital immunologic disorders that have severe neutropenia as a clinical feature include common variable immunodeficiency, the severe combined immunodeficiencies, hyper-IgM syndrome, WHIM syndrome, and a number of even rarer immunodeficiency syndromes (see Table 125-4).

Clinical Manifestations of Neutropenia

Individuals with neutrophil counts <500/µL are at substantial risk for developing infections, primarily from their endogenous flora as well as from nosocomial organisms. Some patients with isolated chronic neutropenia with an ANC <200/µL may not experience many serious infections, probably because the remainder of the immune system remains intact. In contrast, children whose neutropenia is secondary to acquired disorders of production such as with cytotoxic therapy, immunosuppressive drugs, or radiation therapy are likely to develop serious bacterial infections because many arms of the immune system are markedly compromised.

Neutropenia associated with leukopenia, that is, additional monocytopenia or lymphocytopenia, is more highly associated with serious infection than neutropenia alone. The integrity of skin and mucous membranes, the vascular supply to tissues, and nutritional status also influence the risk of infection.

The most common clinical presentation of profound neutropenia includes fever >38°C, aphthous stomatitis and gingivitis, cellulitis, furunculosis, perirectal inflammation, colitis, sinusitis, and otitis media are also frequent accompaniments of profound neutropenia in children. Other clinical manifestations of profound neutropenia include hepatic abscesses, recurrent pneumonias, and septicemia. Isolated neutropenia does not heighten a patient’s susceptibility to parasitic or viral infections or to bacterial meningitis.

The most common pathogens causing infections in neutropenic patients are Staphylococcus aureus and gram-negative bacteria. The usual signs and symptoms of local infection and inflammation such as exudate, fluctuance, and regional lymphadenopathy are generally diminished in the absence of neutrophils because of the inability to form pus. Patients with complete agranulocytosis still experience fever and feel pain at sites of inflammation.

Laboratory Findings

Isolated absolute neutropenia has a limited number of causes (see Tables 125-1 through 125-4). The duration and severity of the neutropenia greatly influence the extent of laboratory evaluation. Patients with chronic neutropenia since infancy and a history of recurrent fevers and chronic gingivitis should have WBC counts and differential counts determined 3 times weekly for 6 wk to evaluate the periodicity suggestive of cyclic neutropenia. Bone marrow aspiration and biopsy should be performed on selected patients to assess cellularity. Additional marrow studies such as cytogenetic analysis and special stains for detecting leukemia and other malignant disorders should be obtained for patients with suspected intrinsic defects in the myeloid progenitors and for patients with suspected malignancy. Selection of further laboratory tests is determined by the duration and severity of the neutropenia and the associated findings on physical examination (see Table 125-1).

Treatment

The management of acquired transient neutropenia associated with malignancies, myelosuppressive chemotherapy, or immunosuppressive chemotherapy differs from that of congenital or chronic forms of neutropenia. In the former situation, infections sometimes are heralded only by fever, and sepsis is a major cause of death. Early recognition and treatment of infections may be lifesaving (Chapter 171).

Therapy of severe chronic neutropenia is dictated by the clinical manifestations. Patients with benign neutropenia and no evidence of repeated bacterial infections or chronic gingivitis require no specific therapy. Superficial infections in children with mild to moderate neutropenia may be treated with appropriate oral antibiotics. In patients who have invasive or life-threatening infections, broad-spectrum intravenous antibiotics should be started promptly.

Subcutaneously administered rhG-CSF can provide effective treatment of severe chronic neutropenia including severe congenital neutropenia, chronic symptomatic idiopathic neutropenia, and cyclic neutropenia. Doses ranging from 2 to over 100 µg/kg/day lead to dramatic increases in neutrophil counts, resulting in marked attenuation of infection and inflammation. rhG-CSF, often at very low doses, may also benefit patients who have immune or drug-induced neutropenias. The long-term effects of rhG-CSF therapy are unknown but include a propensity for the development of moderate splenomegaly, thrombocytopenia, and, occasionally, vasculitis. Autoimmune neutropenia may be responsive to intermittent corticosteroids, especially if it is part of an underlying disease process such as systemic lupus erythematosus.

Patients with severe congenital neutropenia or Shwachman-Diamond syndrome who develop myelodysplasia or acute myelogenous leukemia respond only to allogeneic stem cell transplantation. Chemotherapy is ineffective. Hematopoietic stem cell transplantation is also the treatment of choice for aplastic anemia or hemophagocytic lymphohistiocytosis complicating syndromes discussed earlier.

Lymphopenia

Lymphopenia by itself usually causes no symptoms and is often detected in the evaluation of other illnesses, particularly recurrent viral, fungal, and parasitic infections. Lymphocyte subpopulations can be measured by multiparameter flow cytometry, which uses the pattern of antigen expression to classify and characterize these cells.

Inherited Causes of Lymphocytopenia

Inherited immunodeficiency disorders may have a quantitative or qualitative stem cell abnormality resulting in ineffective lymphocytopoiesis (Table 125-7). Other disorders such as Wiskott-Aldrich syndrome may have associated lymphocytopenia arising from accelerated destruction of T cells. A similar mechanism is present in patients with adenosine deaminase deficiency and purine nucleoside phosphorylase deficiency. Lymphocyte counts may also be decreased in some forms of inherited bone marrow failure, such as reticular dysgenesis, severe congenital neutropenia secondary to GFI1 mutation, or dyskeratosis congenita.

Table 125-7 CAUSES OF LYMPHOCYTOPENIA

ACQUIRED CAUSES

Infectious Diseases

AIDS

Viral hepatitis

Influenza

Tuberculosis

Typhoid fever

Sepsis

Iatrogenic

Immunosuppressive therapy

Corticosteroids

High-dose PUVA therapy

Cytotoxic chemotherapy

Radiation

Thoracic duct drainage

Systemic and Other Diseases

Systemic lupus erythematosus

Myasthenia gravis

Hodgkin disease

Protein-losing enteropathy

Renal failure

Sarcoidosis

Thermal injury

Aplastic anemia

Dietary Deficiency

Dietary deficiency associated with ethanol abuse

INHERITED CAUSES

Aplasia of lymphopoietic stem cells

Severe combined immunodeficiency

Ataxia-telangiectasia

Wiskott-Aldrich syndrome

Immunodeficiency with thymoma

Cartilage-hair hypoplasia

Idiopathic CD4 T lymphocytopenia

ADA, adenosine deaminase; IL-2, interleukin 2; PNP, purine nucleoside phosphorylase; PUVA, psoralen and ultraviolet A irradiation.

From Boxer LA: Approach to the patient with leukopenia. In Humes HD, editor: Kelley’s textbook of internal medicine, ed 4, Philadelphia, 2000, Lippincott Williams & Wilkins, p 1580.

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