Howell-Jolly body

**Definition:** Howell-Jolly bodies (HJBs) are 1 μm, round, dense, basophilic inclusions of residual nuclear DNA in erythrocytes. They stain purple on Wright-Giemsa smear and are Feulgen-positive.

**Pathophysiology:** During erythropoiesis, the normoblast extrudes its nucleus. Occasionally, nuclear fragments (from karyorrhexis or abnormal mitosis) remain in the cell. Splenic macrophages in the red pulp normally "pit" these inclusions out of RBCs without destroying the cell. If splenic function is absent or reduced, or if the spleen is overwhelmed, these RBCs circulate with their inclusions.

**Clinical associations:** - **Functional asplenia:** sickle cell disease (autosplenectomy from repeated infarcts), celiac disease, IBD, splenic infarction or thrombosis, and infiltrative disease (amyloid, sarcoid). - **Anatomic asplenia:** post-splenectomy (surgical or traumatic) and congenital asplenia (heterotaxy syndromes). - **Increased RBC production or abnormal maturation:** megaloblastic anemia (B12/folate deficiency), myelodysplastic syndromes, and severe hemolytic anemias, where marrow output may overwhelm the spleen. - **Other:** neonates, especially premature infants, may have transient HJBs because of an immature spleen.

**Associated smear findings in asplenia:** target cells, acanthocytes, Pappenheimer bodies (iron granules), and thrombocytosis (post-splenectomy). Leukocytosis may also be present.

**Clinical significance (high yield):** - Asplenic patients are at risk of **overwhelming post-splenectomy infection (OPSI)** from encapsulated organisms: *Streptococcus pneumoniae* (most common), *Haemophilus influenzae* type b, *Neisseria meningitidis*, and also *Capnocytophaga canimorsus* (dog bites), *Babesia*, and *Salmonella* (especially in sickle cell). - **Management and prevention:** vaccinate against pneumococcus, *H. influenzae* type b, and meningococcus (ideally ≥2 weeks before elective splenectomy, or ≥2 weeks after emergency splenectomy). Give penicillin prophylaxis in some patients (e.g., children, sickle cell disease) and counsel patients to seek urgent care for fever.

**Differential for RBC inclusions (commonly tested):** - **Howell-Jolly bodies:** DNA remnants; asplenia. - **Heinz bodies:** denatured, oxidized hemoglobin; G6PD deficiency. They need supravital stain (crystal violet), and "bite cells" form when the spleen removes them. - **Pappenheimer bodies:** iron granules (siderosomes); sideroblastic anemia, asplenia. Positive on Prussian blue stain. - **Basophilic stippling:** ribosomal precipitates; lead poisoning, thalassemia, and sideroblastic anemia (e.g., alcohol-related). - **Cabot rings:** microtubule or mitotic spindle remnants; megaloblastic anemia, lead poisoning. - **Reticulocytes:** residual RNA; polychromasia with supravital stain.

**Pearl:** HJBs on a smear in a patient with sickle cell disease indicate a nonfunctional spleen, which raises the risk of encapsulated-organism sepsis. Unexplained HJBs in an adult should prompt a search for celiac disease or other causes of hyposplenism.