We report the case of a child with a venous malformation (VM), in whom streptococcal toxic shock syndrome (STSS) developed from cellulitis. A six-year-old boy with VM of the left lower limb had a fever and left lower limb pain since the afternoon of the day before admission. He presented with swelling, redness, heat, and tenderness on an area extending from the sole of the foot to the lower leg on the left side. Disturbance of consciousness gradually appeared, and he was admitted to the intensive care unit. We administered intravenous antibiotics and an immunoglobulin. On day two of hospitalization, group A hemolytic streptococci were detected in the blood culture. We managed the patient in coordination with a plastic surgeon for consideration of surgical interventions. The local findings subsequently improved to change the antibiotics promptly without debridement, and he was discharged after 14 days of antibiotic therapy. In this case, the VM may have contributed to the worsening of the infection. In children with VM, soft tissue inflammation with local pain and fever must be treated promptly, with the expectation of prompt surgical intervention, because the condition can progress to sepsis and necrotizing fasciitis.

Familial hemophagocytic lymphohistiocytosis (FHL) is a severe inborn error of immunity caused by a genetic defect that impairs the function of cytotoxic T and NK cells. There are only a few reported cases of FHL with diffuse swelling of the cerebellum and obstructive hydrocephalus. We report a case of FHL3 with neurological symptoms associated with cerebellar swelling and obstructive hydrocephalus. A male patient was hospitalized several times due to fever and decreased feeding, hepatosplenomegaly, and cytopenia since the first month of life. At 7 months of age, disturbance of consciousness was seen. Brain magnetic resonance imaging revealed signal intensity in the bilateral cerebellar hemispheres, diffusely increased periventricular white matter, and ventriculomegaly. Although he was treated with methylprednisolone pulse therapy, he was unresponsive to the treatment. He was then transferred to a local hospital after tracheotomy but died. Targeted clinical sequencing revealed a homozygous splice-site mutation in UNC13D. Pediatric hemophagocytic lymphohistiocytosis (HLH) includes some cases of central nervous symptom (CNS)-isolated HLH or CNS HLH preceding systemic lesions, which often do not initially meet the diagnostic criteria for FHL. Patients with FHL initiated by cerebellar symptoms may present with an atypical clinical course for HLH, leading to delayed diagnosis and poor outcomes. Despite the usefulness of a combination of a high percentage of lymphocytes in the peripheral leukocytes, a low lactate dehydrogenase level, and a high sIL-2R/ferritin ratio for identifying FHL, the diagnosis may be missed due to the absence of these results. Presymptomatic diagnosis of FHL by screening of newborns and subsequent early treatment of patients with a predicted poor prognosis may contribute to better outcomes.