asplenia

**Definition and causes** - Anatomic asplenia: surgical splenectomy (trauma, ITP, hereditary spherocytosis, hypersplenism, splenic tumors), or congenital absence (heterotaxy/Ivemark syndrome, often with complex cardiac defects). - Functional asplenia: sickle cell disease (repeated splenic infarcts cause autosplenectomy), also celiac disease, IBD, splenic irradiation, and infiltrative disease (amyloidosis, sarcoidosis).

**Pathophysiology** - The spleen's red pulp filters blood. Splenic macrophages remove opsonized (IgG/C3b-coated) encapsulated bacteria, senescent or abnormal RBCs, and intraerythrocytic inclusions. - The white pulp makes IgM and opsonizing antibodies (the marginal zone B cells respond to polysaccharide antigens). It also produces properdin and tuftsin. - Without the spleen, the body cannot clear encapsulated organisms well, and the response to polysaccharide antigens is blunted.

**Peripheral smear findings (high-yield)** - Howell-Jolly bodies (nuclear remnants in RBCs) - Target cells - Acanthocytes - Pappenheimer bodies (iron granules) and Heinz bodies (denatured hemoglobin) - Thrombocytosis and mild leukocytosis, a post-splenectomy finding

**Clinical significance** - OPSI (overwhelming post-splenectomy infection): fulminant sepsis, often with DIC, adrenal hemorrhage (Waterhouse-Friderichsen) and a high mortality rate. Risk is highest in the first few years after splenectomy but persists for life. - Organisms: *S. pneumoniae* (most common), *H. influenzae* type b, *N. meningitidis*, plus *Capnocytophaga canimorsus* (dog bites), *Salmonella* (especially in sickle cell disease), and *Klebsiella*. - Increased severity of parasitic infection: babesiosis and malaria. - Thrombocytosis raises thrombosis risk, including portal vein thrombosis.

**Management and prevention** - Vaccines: pneumococcal (PCV and PPSV23), Hib, meningococcal (MenACWY and MenB), and annual influenza. - Timing: give vaccines at least 2 weeks before elective splenectomy. After emergency splenectomy, vaccinate about 2 weeks postoperatively. - Antibiotic prophylaxis (penicillin V or amoxicillin) is used mainly in children and in the first 1–3 years post-splenectomy, as well as in patients with sickle cell disease. - Patient education: fever is an emergency. Give empiric antibiotics immediately (e.g., ceftriaxone) for fever or suspected sepsis. Avoid animal bites and consider malaria prophylaxis when traveling. - Consider partial splenectomy or splenic preservation when feasible (e.g., in trauma).

**Board pearls** - Howell-Jolly bodies on a smear = asplenia or hyposplenia. - A patient with sickle cell disease and a fever should be treated as having possible sepsis with an encapsulated organism, and *Salmonella* osteomyelitis is also classic. - Encapsulated organisms mnemonic: "SHiNE SKiS" (S. pneumoniae, H. influenzae type b, N. meningitidis, E. coli, Salmonella, Klebsiella pneumoniae, group B Streptococcus). - Hemolytic anemias such as hereditary spherocytosis may be treated by splenectomy, which helps because the spleen is where the abnormal cells are destroyed.