The case of a Japanese infant who developed hemophagocytic lymphohistiocytosis (HLH) secondary to a bacterial infection highlights the need to consider HLH as a possible complication in such infections — particularly in cases with reduced blood cell counts and/or an enlarged spleen and liver.
The report describing the boy’s case, “Hemophagocytic lymphohistiocytosis complicating invasive pneumococcal disease: a pediatric case report,” was published in the journal BMC Pediatrics.
HLH is characterized by an excessive inflammatory response throughout the body. It can occur on its own, or it can develop secondary to another condition, like cancer or an infection. Most HLH-associated infections that have been reported in existing scientific literature are viral; only a few cases of the condition following a bacterial infection have been reported.
“The incidence of pediatric HLH due to bacterial infections in Japan was reported to be about 6% of the infection-associated HLH cases,” the researchers said.
The new report presents the case of an 11-month-old male, with normal growth and development, who was taken to a family physician after developing a fever. Pneumonia was suspected, and the patient was prescribed antibiotics and sent home. However, the fever persisted, and the child was referred to the hospital.
A battery of diagnostic tests were performed, which found that the boy had abnormally low blood cell counts — termed cytopenia — including low numbers of red blood cells, indicating anemia, and of neutrophils, showing neutropenia. The patient also had an enlarged spleen and liver, together called hepatosplenomegaly, as well as elevated levels of a number of inflammatory molecules in the blood.
Additionally, a bone marrow puncture was performed. Those results showed hemophagocytosis, a phenomenon in which macrophages (a type of white blood cell) in the bone marrow attack other cells — a hallmark of HLH.
A number of viral tests were negative. However, the patient’s blood tested positive for the bacteria Streptococcus pneumoniae — the bacteria that causes invasive pneumococcal disease (IPD).
Based on these results, the boy was diagnosed with severe IPD, and with HLH possibly associated with IPD, or secondary HLH.
Interestingly, a vaccine for IPD exists — the pneumococcal conjugate vaccine, or PCV13 — and the child had previously been fully immunized with three doses. However, PCV13 does not protect against every form of Streptococcus pneumoniae. Test results showed the particular type isolated from the patient — serotype 23A — is not targeted by the vaccine, explaining in part how the child became infected with pneumococcal disease despite being vaccinated.
HLH typically is treated with immunomodulatory therapies that reduce the activity of the immune system. However, in the context of an infection, this can be concerning because reducing immune activity could cause the infection to become more severe.
Nonetheless, because the child “appeared unwell with a severe systemic inflammatory response … we considered immunomodulatory therapy to be vital as an early intervention in the course of the disease,” the researchers said.
Thus, in addition to antibiotics, the patient was given immunosuppressive medication.
After treatment, his blood cell counts increased back to normal ranges, while his fever resolved, and inflammatory blood markers decreased. The boy was discharged from the hospital 22 days after admission, without complications, and with “no recurrence of HLH and no developmental delay” up to age 3, the researchers noted.
“In conclusion, we described a previously healthy boy with secondary HLH caused by IPD with a serotype that is not included in PCV-13,” the scientists said.
“This case suggests that it is important to consider the complication of secondary HLH when children with IPD present with unusual clinical findings, such as a prolonged fever, cytopenia, and hepatosplenomegaly, even if they already received the PCV in the past or have no past medical history,” the team said.
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