Neutropenia and neutrophil disorders: SAQ

This child has febrile severe neutropenia complicating chemotherapy, and he is already showing mottling, so he must be treated as presumed bacteraemic and managed as an emergency in the first hour. The absolute neutrophil count of 0.18 times ten to the ninth per litre sits in the profound-severe band, and his fever of 39.0 degrees Celsius meets the febrile-neutropenia definition. The plan is resuscitation, cultures, and empiric anti-pseudomonal beta-lactam within the first hour, with escalation for his early shock. [1]

Question 1 (10 marks)

Outline your immediate management of this child in the first hour, define the severity of his neutropenia, and explain the mechanism-based classification that frames the broader topic. [1]

The immediate management is the febrile-neutropenia bundle. Assess airway, breathing and circulation; he is mottled, so recognise early shock, remembering that the signs of sepsis are blunted when the neutrophil count is near zero. Take blood cultures from every lumen of the central line and peripherally, send a urinalysis, and obtain a chest radiograph. Start empiric intravenous anti-pseudomonal monotherapy within the first hour: ceftazidime, piperacillin-tazobactam, cefepime or meropenem, weight-dosed by the local oncology protocol, with vancomycin added for suspected line or soft-tissue infection or haemodynamic instability. Resuscitate shock with isotonic crystalloid boluses of 10 mL per kilogram titrated to perfusion, and escalate to vasoactive support and paediatric intensive care if he does not respond. Maintain oral and perianal hygiene and avoid rectal instrumentation. [1]

His neutropenia is severe by definition. Neutropenia is graded by the absolute neutrophil count in three bands: mild 1.0 to 1.5, moderate 0.5 to 1.0, and severe under 0.5, all times ten to the ninth per litre, with infection risk climbing sharply in the severe band and counts under 0.1 considered profound. The absolute neutrophil count is the white cell count multiplied by the percentage of segmented neutrophils plus bands divided by 100. The mechanism-based classification localises the problem to one of four sites: production failure in the marrow (severe congenital neutropenia, marrow infiltration, chemotherapy), peripheral destruction (autoimmune and alloimmune), retention in the marrow (WHIM myelokathexis), or splenic sequestration. This child's mechanism is production failure from chemotherapy. [1]

Question 2 (10 marks)

A separate, well eight-month-old infant of West African ancestry is found on a routine full blood count to have an absolute neutrophil count of 0.7 times ten to the ninth per litre with a normal haemoglobin and platelet count. Discuss the differential diagnosis, the targeted investigations, and the counselling and follow-up. [1][11]

The first step is to confirm the count is real and persistent: repeat the full blood count on a fresh sample, sometimes in citrate or heparin to exclude ethylenediaminetetraacetic-acid clumping, and examine the film for blasts, dysplasia, and the dual neutrophil populations sometimes seen in benign ethnic neutropenia. The differential of an isolated chronic neutropenia in a well infant of this age is led by autoimmune neutropenia of infancy, the commonest chronic isolated neutropenia under three, which presents in an otherwise well child with a median onset around eight months, positive anti-neutrophil antibodies against HNA-1a or HNA-1b, mild to moderate neutropenia, and spontaneous resolution by age four to five. The second contender is benign ethnic neutropenia, common in children of African ancestry through the Duffy-null ACKR1 variant, with a normal marginated pool, normal function, and no infection excess. The third is an inherited disorder such as severe congenital neutropenia, but these present with severe persistent neutropenia under 0.5 from infancy and recurrent infections, which does not fit this well infant with a moderate count. [1][11]

The targeted investigations are anti-neutrophil antibodies, an immunoglobulin and lymphocyte subset, a vitamin B12, folate and copper level, and, if the neutropenia is severe or persistent or accompanied by other cytopenias, a bone marrow with cytogenetics and an inherited neutropenia gene panel covering ELANE, HAX1, SBDS, CXCR4, GATA2, LYST and TAZ. The counselling depends on the result. For autoimmune neutropenia of infancy, reassure the family that the course is benign and self-limiting, give a clear safety-net to return if fever or severe infection occurs, and monitor until resolution. For benign ethnic neutropenia, document the diagnosis in the record, explain that it is a normal variant with no infection excess and no treatment, and protect the child from over-investigation and from being wrongly excluded from school or sport. For a febrile episode in a child with any of these, the safety-net is the same: fever must be assessed urgently, because a severe neutropenia with fever is an emergency regardless of the underlying diagnosis. [1][11]