Pediatric Clinics of North America - CIPERJ

506 TRACY & RICE
and antibodies against T-independent antigens, such as pneumococcal polysaccharides
[24–26]. Natural antibodies primarily are IgM, are independent
of previous immunization, bind antigens with low affinity, and limit infections
before generation of specific antibody [27,28]. IgM memory B cells
correspond to circulating splenic marginal zone B cells and are lacking in
patients who do not have a spleen [25,29]. The absence of IgM memory
B cells correlates with diminished serum antipneumococcal polysaccharide
IgM antibody responses in splenectomized patients [24].
The specific clinical benefits of splenic-mediated immune function are
demonstrated in children who have common variable immunodeficiency
(CVID), a heterogeneous immune disorder of unknown pathogenesis characterized
by the inability to mount protective antibody responses in the presence
of normal numbers of circulating B cells. Recent studies of CVID and
related conditions have demonstrated further the critical function of splenicmediated
IgM memory B cells. In these children, IgM memory B cells seem
essential for prevention and control of common childhood infections, such
as those of the respiratory tract caused by encapsulated bacteria [24].
Memory B cells are lacking in infants and children who have CVID and
in children who are asplenic. It seems, therefore, that surgical interventions
for the management of HS that avoid rendering patients asplenic would
have far-ranging implications not only in reducing the incidence of the
rare but lethal cases of OPSI but also possibly in reducing the more common
infections that affect children.
Complications of total splenectomy and risks for overwhelming
postsplenectomy infection
Total splenectomy carries significant risks for children and adults. The
most well-known and feared complication of total splenectomy is OPSI,
characterized by multisystem organ failure after invasive infection with
encapsulated bacteria, such as Streptococcus pneumoniae. OPSI is lethal in
the majority of affected children. The risk for OPSI is higher for children
compared with adults and may be as high as 20% for children who undergo
splenectomy before the age 5 [3–6]. The rate of sepsis in children less than
5 years of age who have undergone total splenectomy is 60-fold to 100-fold
higher than for children who have not had a splenectomy [5].
Although the risk for OPSI is reduced by the use of immunizations
against Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae
type b, and postoperative antibiotic prophylaxis, its risk never is
eliminated fully. Despite the frequent belief that older children and adults
are not affected adversely by asplenia, patients who undergo splenectomy
remain at lifelong increased risk for overwhelming infection [6,23]. The
risk is compounded by the fact that vaccinations do not provide complete
protection, antibiotic resistance may emerge, and poor compliance with recommended
antibiotic prophylaxis often is observed [6,30].