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Asplenic individuals are at risk of developing overwhelming bacterial sepsis with capsulated organisms such as Streptococcus pneumoniae,1 against which pneumococcal vaccination or antibiotic prophylaxis can provide life-saving protection. Opportunities to identify such individuals should thus be vigorously pursued.
A well-nourished male infant, age 22 months, reached our intensive care unit in uncompensated septic shock following a 3-day illness of diarrhoea and vomiting (with fever for 2 days). Despite vigorous resuscitative efforts that included antibiotics (ceftriaxone), early intubation and ventilation, fluid resuscitation (100 mL/kg), maximal inotropic support including vasopressin, and corticosteroids, the child died six hours after admission. Streptococcus pneumoniae, sensitive to ceftriaxone, was isolated from antemortem blood cultures and pneumococcal antigens were detected in postmortem blood samples.
After the death, we discovered that the child had had one previous invasive pneumococcal infection (meningitis) at 10 months of age from which he had recovered fully. At that time his immune status had been assessed. Serum complement, immunoglobulins and IgG subclass levels were all normal, but evidence for asplenia was not sought. At necropsy the child was found to have only vestigial splenic tissue—very small nubbins which histologically showed occasional follicles and haemorrhagic red pulp but consisted mainly of fibrous scar tissue. The appearance of the spleen was consistent with infarction at some stage, either in utero or ex utero, and a rather thin hilum at risk of torsion indicated the possible mechanism. There was no history of splenectomy or sufficient trauma, nor any history of sickle cell disease or other potential cause of autosplenectomy to explain these findings. The adrenals showed extensive haemorrhage. There was no evidence of pneumonia or meningitis.
Clinicians are well versed in the need for protection against S. pneumoniae where the spleen is known to be absent, either through functional asplenia as in sickle-cell anaemia or acquired asplenia after trauma or surgery. Congenital asplenia may occur as an isolated condition, in recognized malformation syndromes or in family clusters.2 Where a syndrome or family history alerts the clinician to possible asplenia, confirmatory investigations should lead to effective prophylaxis. Our patient had no siblings and had no family history of pneumococcal disease. Individuals with isolated congenital asplenia are, by contrast, brought to the clinician's attention only when they have experienced one or more episodes of invasive infections from capsulated bacteria.3 Some clinicians judge that, even after a single episode of S. pneumoniae sepsis, investigation for asplenia is mandatory.4
Asplenia is diagnosed through two easy and non-invasive investigations—a search for Howell–Jolly bodies on blood smears, which are characteristic of but not specific for asplenia, or abdominal ultrasound. Can this be reasonably achieved? During the past 12 months, in our institution, S. pneumoniae was isolated from samples from normally sterile sites in 16 child patients, which by inference would necessitate the same number of additional abdominal ultrasound examinations, a further case load of only one or two per month. This together with 16 additional blood smears in a year should be easily achieved within current resource. The yield is likely to be low: in one study of 2498 paediatric patients with invasive pneumococcal disease only 0.8% were known to have asplenia5 (though the authors did not apparently search actively for asplenia). Nevertheless, there is likely to be a major benefit for the rare affected patient—particularly since the conjugate pneumococcal vaccines are likely to add to the protection given by antibiotic prophylaxis.
This case provides a reminder to pursue asplenia as a potential underlying mechanism for invasive bacterial infection in children. We believe that abdominal ultrasound should be performed in addition to the blood tests usually recommended for immune function screening after such an episode. Such a guideline, if widely instituted, might not only prevent deaths but also provide information on the incidence of unrecognized asplenia presenting with invasive pneumococcal infection.