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Pediatric Diseases: Baby Autoimmune Neutropenia

Disease which repeats mild affection.

Autoimmune Neutropenia Disease Autoimmune Neutropenia disease may often occur among babies. In general, autoimmune neutropenia disease is defined as the absolute numbers of peripheral blood neutrophil(ANC) is less than 1,500/µL. In case when ANC becomes less than 500/µL, it is subject to compromised disease, when less than 200/µL, it turns to severe condition so that infection disease may repeat. It becomes necessary for baby’s case to distinguish Severe Congenital Neutropenia (SCN) and Autoimmune Neutropenia (AIN).

Severe Congenital Neutropenia (SCN) is a genetically influenced disease, and especially, there are many cases in which numbers of peripheral blood neutrophil becomes less than 200/µL, so that the clinical characteristic is the recurrent of bacterial infectious disease after birth. Regarding the bone marrow, there is an aberrant maturation at promyelocyte or myelocytic stage, and they bear evidence of stab cell or segmented neutrophil are drastically decreased. Diagnosis is established by genetic diagnosis.

On the other hand, Autoimmune Neutropenia Disease (AIN) merely makes numbers of peripheral blood neutrophil under 200/µL, instead, it is a disease where numbers of peripheral blood neutrophil at less than 500/µL continues for few months, thus showing clinically mild susceptibility to infection. Most of them is developed in late babyhood to childhood stage. The positive antineutrophil antibody in blood serum is the lead for the diagnosis.

Cause of AIN is the destruction of Neutropenia by autoantibody

In general, neutropenia is developed by several causes (fig.1) and summarized as below.

Severe congenital neutropenia (SCN) is developed by gene variant called as ELANE or HAXI, but autoimmune neutropenia (AIN) is an autoimmune disease that the increased destruction of neutrophil is developed by production of autoantibodies against the surface molecule of neutrophil. Because they are most of all antibody against the neutrophil specific antigen in which matured neutrophil is developed, unlike SCN when checking at myelogram, remarkable characteristic is that the stab neutrophil exists but segmented neutrophil is decreased drastically.

Mostly mild case so that it recovers by 5 years old.

There is a case that increased susceptibility to infection along with neutropenia is recognized, and bacterial infection, such as inflammation of the upper airway or inflammation of the middle ear, may iterate, but most of the cases they are mild.

Autoimmune Neutropenia (AIN) in babyhood will take a good clinical course with getting neutropenia to mild one along with natural disappearance of antineutrophil antibody in almost all case. Approximately 80 % of them will get recovered by 3 years old, and in almost all cases numbers of neutrophil is increased by 5 years old.

Myelogram is helpful in differentiating SCN.

好中球抗原はHNA-1,HNA-2 など数種類が同定されています。Fcγ receptor IIIb(CD16b)上に存在するHNA-1 系に対する抗体が原因となることが少なくなく、HNA-1a抗体とHNA-1b抗体が検出可能といわれています。骨髄像は重症先天性好中球減少症(SCN)と自己免疫性好中球減少症(AIN)の鑑別に役立ちます。HNA検査も普通の病院では行えないので、検査可能な施設に依頼する必要があります。

Steroid or immune-suppressing drug are unnecessary.

Amongst baby neutropenia, severe congenital neutropenia is subject to hematopoietic stem cell transplant. However, because of autoimmune neutropenia (AIN) has less provability to comorbid with severe infection disease, administering appropriate antibiotic when acquiring an infection is the usual treatment. Also, ST compound drug is administered to prevent bacterial infection. If by any chance severe infection is developed, G-CSF administer is combined. There might be a case where steroid or immune-suppressing drug is used for adult autoimmune neutropenia, but they are unnecessary for baby AIN.

Fig. 1