Neutropenia and neutrophil disorders: Viva

Branch 1: The first move and the definition

The candidate should immediately reframe the picture: an incidental isolated neutropenia in a well infant two weeks after a viral illness, most likely a benign transient post-viral dip, but to be confirmed. The first move is to repeat the full blood count on a fresh sample and to examine the peripheral film, because ethylenediaminetetraacetic-acid clumping and transient post-viral dips are common, and a single low count is never a diagnosis. The candidate should state the thresholds aloud: neutropenia is an absolute neutrophil count under 1.5 times ten to the ninth per litre, graded as mild 1.0 to 1.5, moderate 0.5 to 1.0, and severe under 0.5, with the absolute neutrophil count calculated as the white cell count times the percentage of segmented neutrophils plus bands divided by one hundred. [1]

The examiner will probe why the count is calculated and why the bands matter. The candidate should explain that the circulating pool is the fraction sampled by a full blood count, that the marginated pool is roughly equal in size, and that including the band cells in the absolute neutrophil count matters because they are the immediate neutrophil reserve. The examiner may ask what a low count in a child of African ancestry means. The candidate should name benign ethnic neutropenia, caused by the Duffy-null regulatory variant in the ACKR1 gene, with a normal marginated pool and normal function and no infection excess, and stress that recognising it prevents over-investigation. [11]

Branch 2: The kinetic model and the mechanism

The examiner will ask the candidate to explain how neutropenia arises. The candidate should walk the neutrophil kinetic pipeline: production in the marrow through the myeloid maturation cascade over ten to fourteen days, release into the circulating pool, the marginated pool, and egress to the tissues. A drop in the count means one of four things: production failure in the marrow (severe congenital neutropenia, marrow infiltration, chemotherapy), peripheral destruction (autoimmune and alloimmune), retention of mature cells in the marrow (WHIM myelokathexis), or splenic sequestration. The examiner will reward a candidate who names the four sites rather than listing causes at random. [1]

The examiner may press on the mechanism of severe congenital neutropenia. The candidate should explain that ELANE mutations cause misfolded neutrophil elastase that triggers unfolded-protein-response apoptosis of the promyelocyte, producing a maturation arrest at the promyelocyte stage and severe persistent neutropenia from infancy. The examiner may then ask how cyclic neutropenia differs, and the candidate should say that it shares the ELANE mechanism but oscillates on a roughly twenty-one day cycle through a feedback loop, with mouth ulcers and fever clustering at the predictable nadir. [5]

Branch 3: The workup and the gene panel

The examiner will ask how the candidate works up a chronic isolated neutropenia in a well infant. The candidate should first split isolated from pancytopenic, because pancytopenia points to marrow failure or infiltration and needs an urgent bone marrow. For the isolated case, the targeted tests are anti-neutrophil antibodies for autoimmune neutropenia of infancy, immunoglobulins and a lymphocyte subset for associated immune deficiency, an antinuclear antibody and double-stranded DNA for secondary autoimmune causes, and vitamin B12, folate and copper for the nutritional causes. [1]

The examiner will ask when to do a bone marrow and a gene panel. The candidate should state that a bone marrow aspirate and trephine with cytogenetics is obtained when the neutropenia is severe and persistent, part of a pancytopenia, or accompanied by dysplasia or blasts. The candidate should name the inherited neutropenia gene panel: ELANE, HAX1, SBDS, CXCR4, GATA2, LYST and TAZ. The examiner may probe a specific syndrome: Shwachman-Diamond pairs neutropenia with exocrine pancreatic insufficiency, skeletal dysplasia and short stature, and is caused by SBDS; Chediak-Higashi shows partial albinism, giant intracytoplasmic granules, and a risk of a fatal accelerated phase, and is caused by LYST. [2]

Branch 4: The management and the counselling

The examiner will ask how the candidate manages autoimmune neutropenia of infancy. The candidate should say the management is expectant, because the condition resolves spontaneously in the great majority by age four to five; granulocyte colony-stimulating factor, intravenous immunoglobulin or corticosteroids are reserved for the child with severe or recurrent infections. The counselling reassures the family, gives a clear safety-net for fever, and monitors until resolution. The examiner will press on the safety-net, and the candidate should state that any fever in a child with neutropenia is assessed urgently, because a severe neutropenia with fever is an emergency regardless of the underlying diagnosis. [1]

The examiner may pivot to severe congenital neutropenia. The candidate should state that the cornerstone is lifelong granulocyte colony-stimulating factor (filgrastim or lenograstim) subcutaneously, started at a low dose and titrated to a protective absolute neutrophil count, with annual marrow surveillance with cytogenetics for the cumulative risk of myelodysplastic syndrome and acute myeloid leukaemia of roughly twenty per cent over ten years on therapy. Haematopoietic stem cell transplant is the curative option for the syndromes with marrow failure, immunodeficiency or leukaemic transformation. The candidate should close by affirming that the prognosis of the benign causes is excellent, that benign ethnic neutropenia needs only recognition, and that the single non-negotiable action point across the whole topic is the first-hour empiric antibiotic for the febrile severely neutropenic child. [3][1]