**3. Etiologies of severe neutropenia**

In adults, the diagnosis of acute and severe neutropenia (neutrophil count of <0.5 × 109 /L includes a limited number of conditions [1]. In fact, the main differential diagnoses outside the context of treatment of cancer with chemotherapy (e.g., alkylating agents, antimetabolites, etc.) or radiotherapy, include myelodysplastic syndromes, especially in elderly patients, and acute leukemia.

All other conditions induced moderate neutropenia, with an absolute neutrophil count between 1.5 and 0.5 × 109 /L. These conditions mainly include: neutropenia secondary to sepsis, particularly viral infections or bacterial infections (severe Gram-negative infections with Salmonella sp., tuberculosis, Brucella sp.); and neutropenia associated with hypersplenism [2]. Other rarer differential diagnoses include neutropenia secondary to alcoholism, nutritional deficiencies (folic acid, vitamin B12, cooper, etc.), Felty's syndrome, systemic lupus erythematosus or Sjögren's syndrome, and lastly aplastic anemia or paroxysmal nocturnal hemoglobinuria [2].

In the literature, acute and severe neutropenia has been shown to be attributable to drugs in 70–90% of cases [2]. Thus, in practice, idiosyncratic drug-induced neutropenia or agranulocytosis should be discussed routinely (considered in first) even if there is a context moving toward another condition.
