Asplenia

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Summary of Asplenia

Asplenia refers to the absence of normal spleen function and is associated with some serious infection risks. Hyposplenism is used to describe reduced splenic functioning, but not as severely affected as with asplenism. Asplenia is a form of immunodeficiency, increasing the risk of sepsis from polysaccharide encapsulated bacteria, and can result in overwhelming post-splenectomy infection, often fatal within a few hours. In particular, patients are at risk from Streptococcus pneumoniae, Haemophilus influenzae, and meningococcus. The risk is elevated as much as 350–fold. Increased platelet counts can be seen in individuals without a functioning spleen.

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ASPLENIA osms.it/asplenia PATHOLOGY & CAUSES ▪ Absence of normal spleen → immunodeﬁciency ▪ Splenic macrophages loss → inability to clear opsonized bacteria from blood ▪ T-cell independent antibodies deﬁciency ▪ Increased infection risk, severity from polysaccharide encapsulated bacteria ▫ Haemophilus inﬂuenzae type b, Streptococcus pneumoniae, Neisseria meningitidis, Group B streptococcus, Klebsiella pneumoniae, Salmonella typhi TYPES Acquired asplenia ▪ Splenectomy ▫ Surgical procedure, spleen partially/ completely removed (following trauma, cancer, hemoglobinopathies, massive enlargement) ▪ Auto-splenectomy ▫ Underlying disease → focal venous occlusion → repeated infarction → gradual perivascular ﬁbrosis → loss of function (e.g. sickle-cell disease, pneumococcal septicaemia, systemic lupus erythematosus) Congenital asplenia (rare) ▪ Heterotaxy syndrome (situs ambiguus) → disruption to splenic development during embryogenesis → no spleen/formation of multiple ineffective spleens → functional asplenia ▪ Isolated congenital asplenia → ribosomal mutation → failure of spleen development Functional asplenia ▪ Splenic tissue present, functionally impaired (e.g. sickle-cell disease, isolated congenital asplenia) Hyposplenism 452 OSMOSIS.ORG ▪ Reduced splenic function, less severe SIGNS & SYMPTOMS ▪ Recurrent infection ▪ Sickle cell disease ▫ Enlarged palpable spleen DIAGNOSIS DIAGNOSTIC IMAGING ▪ Abdominal ultrasound, CT scan/MRI ▪ Radionuclide scan ▫ Assess for function LAB RESULTS ▪ Thrombocytosis (elevated platelet count), leukocytosis (elevated white cell count) ▪ Howell–Jolly bodies ▫ Erythrocytes containing basophilic DNA fragments ▪ Target cells ▫ Erythrocytes with increased ratio of surface membrane area to volume TREATMENT MEDICATIONS Antibiotics ▪ Antibiotic prophylaxis (penicillins) ▪ Early antibiotic prescription at ﬁrst sign of infection (common/otherwise) Vaccination ▪ Pneumococcal polysaccharide vaccine ▪ Haemophilus inﬂuenzae type b vaccine ▪ Meningococcal conjugate vaccine ▪ Inﬂuenza vaccine

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Asplenia

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A 31-year-old man is brought to the emergency department by coworkers for stupor and unresponsiveness starting earlier in the day. He had been previously healthy until developing flu-like symptoms three days before admission. Past medical history is significant only for splenectomy, performed without complications ten years ago after traumatic rupture. His vital signs are as follows: temperature 39.9°C (103.8°F), pulse 160/min, respirations 28/min, and blood pressure 75/30 mm Hg. Physical examination shows central truncal flushing with peripheral coolness. Which of the following choices describes the pathogen that best explains his symptoms?

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