Neutropenia overview

# Overview
Neutropenia is a hematological disorder characterized by an abnormally low number of neutrophil granulocytes (a type of white blood cell). Neutrophils usually make up 50-70% of circulating white blood cells and serve as the primary defense against infections by destroying bacteria in the blood. Hence, patients with neutropenia are more susceptible to bacterial infections and without prompt medical attention, the condition may become life-threatening. Neutropenia can be acute or chronic depending on the duration of the illness. A patient has chronic neutropenia if the condition lasts for greater than 3 months. It is sometimes used interchangeably with the term leukopenia. However, neutropenia is more properly considered a subset of leukopenia as a whole. Some patients, such as those with constitutional/benign ethnic neutropenia, suffer relatively few complications, however neutropenia related to cytotoxic chemotherapy, hematopoietic stem cell transplant, or other causes of bone marrow suppression may present as a medical emergency.

# Historical Perspective
Neutropenia was first noted around the start of the 20th century on review of blood cell differentials described in patients with lupus, other autoimmune disorders, and with various drug toxicities.

# Classification
Calculated based on blood count differential, neutropenia is defined as an absolute neutrophil count (ANC) less than 1,500 cells per microliter and is calculated by multiplying the total white blood cell (WBC) count by the percentage of neutrophils (including both mature neutrophils and band forms).
- Mild Neutropenia: ANC 1,000-1500 cells/microliter
- Moderate Neutropenia: ANC 500-1000 cells/microliter
- Severe Neutropenia (Agranulocytosis): ANC <500 cells/microliter

# Pathophysiology
Neutropenia develops as a result of one of the three following mechanisms:
- Impaired granulocyte production
Hematologic malignancy with bone marrow infiltration
Myelosuppressive chemotherapy or other medications that are toxic to the bone marrow
Nutritional deficiencies
- Hematologic malignancy with bone marrow infiltration
- Myelosuppressive chemotherapy or other medications that are toxic to the bone marrow
- Nutritional deficiencies
- Margination: (process where free flowing blood cells exit circulation)
Splenic sequestration
Adherence to the vascular endothelium
- Splenic sequestration
- Adherence to the vascular endothelium
- Peripheral destruction
Autoimmune hemolysis
Drug-induced hemolysis
- Autoimmune hemolysis
- Drug-induced hemolysis

# Causes
The most common etiologies are constitutional or benign ethnic neutropenia (BEN) and drug-induced neutropenia. While the former is typically benign, as the title suggests, and not associated with significant complications, drug-induced neutropenia is often related to underlying cancer or medications that can suppress the bone marrow and can be severe and life-threatening if not identified and treated urgently.

# Epidemiology and Demographics
Neutropenia is typically identified in at-risk patients undergoing cytotoxic chemotherapy or on other myelosuppressive medications. As noted above, some ethnicities have an unusually high prevalence of incidentally identified mild neutropenia, also termed constitutional or benign ethnic neutropenia (BEN).  This is most common in blacks, Yemenites, West Indians, and Arab Jordanians and is suggested to be caused by a mutation in the Duffy antigen on red blood cells that helps to confer resistance to malaria.  As the name suggests, these cases are typically mild and do not result in immunosuppression.

# Screening
There are no routine screening recommendations for neutropenia. Neutropenia is typically identified incidentally on routine blood work or while monitoring after cytotoxic therapy.

# Natural History, Complications and Prognosis
Neutropenia is a frequent finding on blood differential. When identified, attention must be placed on identifying underlying medication toxicities, autoimmune disorders or hematological malignancies, or various infections. While most patients with mild neutropenia recover quickly and without complications, severe medication-related neutropenia can be fatal in up to 10%. Close attention must be given to identifying poor prognostic indicators, early signs of infection, and any cyclic pattern to this hematologic abnormality to avoid potentially fatal complications.
Febrile neutropenia is an often fatal complication of severe neutropenia, with fever often being the only presenting symptom of an underlying infection.

# Diagnosis
In patients with severe neutropenia, the neutrophil-mediated inflammatory process in the setting of infection is often blunted.  Fever can be the sole presenting symptom.  The risk of infection increases with the degree and duration of neutropenia with prolonged neutropenia defined as >7 days.
Per 2002 IDSA  and 2013 ASCO  guidelines, febrile neutropenia requires both of the following criteria:
- Fever: single oral temperature >38.3 C/101 F or sustained temperature >38 C/100.4 F for 1 hour.
- Severe neutropenia: ANC< 500 cells/microliter.

## History and Symptoms
Neutropenia can go undetected until the patient develops secondary, and often severe, infections or sepsis. Some common infections can take an unexpected course in neutropenic patients; formation of pus, for example, can be notably absent, as this requires circulating neutrophil granulocytes.  
History should focus on symptoms suggestive of malignancy or infections, patient or family history of autoimmune or immunodeficiency disorders, risk factors for infections including HIV and hepatitis, and any unusual dietary practices or history of bariatric surgery.  Medications should be reviewed with particular attention to chemotherapeutics, antibiotics, antiepileptics, and psychoactive drugs as well as documenting any new medications started within the preceding few months.
Common presenting symptoms in neutropenic patients include:
- Fever
- Frequent infections due to lessened ability to fight bacterial infections
- Mouth ulcers
- Diarrhea
- Burning sensation when urinating
- Unusual redness, pain, or swelling around a wound
- Sore throat
- Shortness of breath
- Shaking chills

## Physical Examination
Physical examination should focus on identifying any potential signs of infection and is directed by the patients' presenting symptoms.  A rectal examination should not be performed in a patient with neutropenia.

## Laboratory Findings
Neutropenia is detected on a full blood count. A peripheral blood smear is often useful to evaluate for abnormal morphology of the visible cells, which may help suggest the underlying cause. Additional laboratory studies include evaluation of metabolic abnormalities, genetic causes neutropenia, and toxic causes.

## Imaging Findings
Neutropenia is not identified on or correlated with any particular imaging. In the cases of neutropenic fever, imaging findings are dependent upon the source of the fevers. Initial evaluation for neutropenic fever should include chest radiography to evaluate for pulmonary infiltrates or effusions.  Further imaging, such as CT or MRI scans, are indicated depending upon presenting symptoms and physical examination findings.

## Other Diagnostic Studies
Other diagnostic studies for neutropenia include bone marrow biopsy, which may be helpful when the etiology is uncertain, or serious causes such as malignancy and marrow replacement are suspected.

# Treatment

## Medical Therapy
There is no specific therapy for neutropenia itself aside from removing the offending agents in drug-induced cases and treating the underlying disease in other, however recombinant G-CSF (granulocyte-colony stimulating factor) can be considered to speed myeloid reconstitution.
Asymptomatic, mild to moderate neutropenia can often be monitored closely on an outpatient basis with serial CBCs and evaluation for medications, infections, or alternative sources of neutropenia as described in detail above.  Offending medications are often held and the patient is monitored for response to discontinuation while evaluating for alternative, more concerning etiologies. With mild neutropenia, medications can often be reintroduced after neutrophil counts recover as the neutropenia is typically dose-dependent.
Patients who are febrile, acutely ill, or with severe neutropenia often warrant urgent hospitalization for close monitoring and treatment.  Offending medications must be discontinued as drug-induced agranulocytosis presents up to a 10% mortality and is very likely to recur if the offending agent is restarted.

## Complications
There are no intrinsic complications of neutropenia, however people who are neutropenic are at risk for infections and febrile neutropenia.

### Febrile Neutropenia
- Ciprofloxacin 500mg PO BID + amoxicillin/clavulanate 500mg PO TID
- Cefepime 2 g IV Q8H
- Meropenem 1 g IV Q8H
- Imipenem/cilastatin 500 mg IV Q6H
- Piperacillin/tazobactam 4.5 g IV Q6H
- Ceftazidime 2 g IV Q8H (recent data shows increasing resistance to ceftazidime and inferior Gram-positive coverage to alternative regimens)
- Hemodynamic instability
- Suspected catheter-associated infection
- Mucositis or cellulitis
- Pneumonia
- History of MRSA infection or colonization
- Gram-positive bacteremia prior to final culture results
- Recent fluoroquinolone prophylaxis
- Re-evaluate sources of infection
- Re-evaluate indications for resistant Gram-positive coverage and consider adding vancomycin or linezolid.
- Re-evaluate indications for resistant Gram-negative organisms and anaerobes and consider broadening to carbapenem antibiotics.
- Consider fungal coverage in high risk patients if fevers persist after 4-7 days of appropriate antibiotic coverage and duration of neutropenia is expected to last >7 days. :Consider the following antifungals.
Caspofungin 70 mg IV x 1 dose, then 50mg IV daily
Liposomal Amphotericin B 3 mg/kg/day
Voriconazole 6 mg/kg IV Q12H x 2 doses, then 4 mg/kg IV Q12H
- Caspofungin 70 mg IV x 1 dose, then 50mg IV daily
- Liposomal Amphotericin B 3 mg/kg/day
- Voriconazole 6 mg/kg IV Q12H x 2 doses, then 4 mg/kg IV Q12H
- Documented infection: Continue antimicrobials as directed by culture data. Continue treatment for the standard duration for that particular infection and until myeloid recovery (ANC>500 cells/microliter). If counts recover prior to completing the treatment course, consider transition to an oral regimen guided by culture data.
- Negative Cultures: Continue empiric antimicrobial regimen until myeloid recovery (ANC>500 cells/microliter). If afebrile with no evidence of ongoing infection, consider transition to oral regimen (e.g. Ciprofloxacin + Amoxicillin/Clavulanate) and continue until myeloid recovery.

## Surgery
There are no surgical treatments for neutropenia. In patients' with neutropenic fever, surgical intervention may be necessary depending on the sources of their infections.

## Primary Prevention
Prevention of neutropenia is dependent upon avoiding certain medications or treatment of underlying conditions.

## Secondary Prevention
Secondary prevention of neutropenia relies on careful avoidance of triggers, such as certain medications, or treatment of underlying conditions. Further discussion of the causes of neutropenia are reviewed above.