Agranulocytosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Agranulocytosis (literally meaning an increase of agranulocytes or more commonly, a lack of granulocytes) is an acute condition involving a severe and dangerous leukopenia (reduction in the number of white blood cells) in the body. Concentrations of granulocytes (a class which includes neutrophils, basophils and eosinophils) can often drop to below 500 cells/mm³ of blood), less than a sixth of the reference value of 3-10 x 103 cells/mm³.
Signs and symptoms
Agranulocytosis may be asymptomatic, but may clinically present with sudden fever, rigors and sore throat. Infection of any organ may be rapidly progressive (e.g. pneumonia, urinary tract infection). Septicemia may also progress rapidly.
A large number of drugs have been associated with agranulocytosis, including antiepileptics, antithyroid drugs (carbimazole and methimazole), metamizole, antibiotics (penicillin, chloramphenicol and co-trimoxazole), cytotoxic drugs, gold, NSAIDs (indomethacin, naproxen, phenylbutazone) some antipsychotics (the atypical antipsychotic clozapine), whose users must be nationally registered for monitoring of low WBC and absolute neutrophil counts (ANC), and the antidepressant mirtazapine (Remeron). Although the reaction is generally idiosyncratic rather than proportional, experts recommend that patients be told about the symptoms of agranulocytosis (generally starting with a sore throat and a fever).
Neutropenia and agranulocytosis are associated with gum disease.
Diagnosis
The diagnosis is made on a complete blood count, a routine blood test performed frequently in general practice and especially in hospital setting.
The neutrophil count is below 500 and can reach 0 cells/mm3. Other series are generally spared. The myelogram (bone marrow sample) shows normocellular blood marrow with promyelocyte's maturation arrest. To formally diagnose agranulocytosis, other pathologies with a similar presentation must be excluded, such as aplastic anemia, paroxysmal nocturnal hemoglobinuria, myelodysplasia and acute leukemia; this generally requires a bone marrow examination.
Classification
The terms "agranulocytosis", granulocytopenia, and neutropenia are often used interchangeably, although "agranulocytosis" implies a more severe deficiency than "granulocytopenia", and "neutropenia" implies a deficiency of neutrophils only. To be precise, neutropenia is the term used to describe absolute neutrophil counts (ANC) <500 per microlitre. Whereas, agranulocytosis is reserved for cases with ANC <100 per microlitre. The following terms can be used to specify the type of granulocyte referenced:
- neutrophil -- neutropenia
- eosinophil -- eosinopenia - not commonly used
- basophil -- basopenia - very rarely used
Treatment
In patients who have no infective symptoms, management consists of close moniting with serial blood counts, withdrawal of the offending agent (e.g. medication) and general advice on the significance of fever.
Infection in patients with low white blood cell counts is generally treated urgently, and usually includes a broad-spectrum penicillin or cephalosporin (piperacillin-tazobactam, ceftazidime or ticarcillin clavulanate) or meropenem in combination with gentamycin or amikacin.
If the patient remains febrile after 4-5 days and no causative organism for the infection has been identified, antibiotics are generally changed to a glycopeptide (e.g. vancomycin), and subsequently an antifungal agent (e.g. amphothericin B) is added to the regimen. In agranulocytosis, the use of recombinant G-CSF (filgrastim) often results in hematologic recovery.