neutropenia

introduction

usually defined as absolute neutrophil count < 0.5 × 10⁹/L (aka agranulocytosis)
it is important as the risk of serious bacterial infection increases as the neutrophil count falls below this level.
a person with a fever who is neutropenic or has a rapidly falling neutrophil count as above, is at particular risk for serious infection and should be urgently managed as per febrile neutropenia

drugs and toxins are among the most common causes of acquired neutropenia, but one must differentiate mild, dose-related neutropenia from idiosyncratic agranulocytosis
either via an immune-mediated or cytotoxic effect resulting in agranulocytosis or aplastic anaemia
cytotoxic agents
antibiotics such as penicillins, cephalosporins, sulphonamides, macrolide antibiotics, chloramphenicol, etc
quinidine, procainamide
antithyroid medications
phenothiazines
clozapine
antidepressants
anticonvulsants
diuretics
hydralazine
aspirin (acetylsalicylic acid), non-steroidal anti-inflammatory drugs (NSAIDs)
ticlopidine
various chemical exposures
many others

B12 or folic acid / folate but rarely occurs without concomitant macrocytosis and pancytopenia
copper - most commonly found in patients who have undergone certain types of gastric bypass surgery
anorexia nervosa / eating disorders

cyclic neutropenia
- rare, AD, alternate 2-5 week cycling of neutrophils and monocytes which is relatively constant cycle duration for a given patient
- some patients can develop infections or mouth ulcers at the nadir
benign familial neutropenia
- unknown genetic basis
constitutional or ethnic neutropenia
- mild, chronic neutropenia with ANC > 1.0
- mainly in those from Mediterranean or African ethnicity
Kostmann syndrome
severe congenital neutropenia (SCN)
- a group of inherited disorders characterized by agranulocytosis and recurrent, severe infections that begin during infancy
- Rx is usually with G-CSF injections
- 10-30% lifetime risk of AML
many other rare conditions (most are diagnosed in childhood) such as:
- Shwachman-Diamond syndrome, Fanconi anaemia, dyskeratosis congenita, Chediak-Higashi syndrome, myelokathesis, Griscelli syndrome II, and cartilage-hair hypoplasia

Hemophagocytic Lymphohistiocytosis (HLH)
- can cause potentially lethal multi-organ failure and can have many causes, esp. in those genetically predisposed
- usually also has other low cell counts, splenomegaly, hypertriglyceridemia and/or hypofibrinogenemia, and Haemophagocytosis