Mycoplasma pneumoniae-triggered hemophagocytic lymphohistiocytosis complicated by type I plastic bronchitis in a child: a case report
- 1Department of Pediatric Respiratory Medicine, Children’s Hospital, Tianjin University/Tianjin Children’s Hospital
- 2Pediatric Hematology Department, Children’s Hospital, Tianjin University/Tianjin Children’s Hospital
Abstract
Background: Hemophagocytic lymphohistiocytosis (HLH) triggered by Mycoplasma pneumoniae (MP) is exceptionally rare in children, with fewer than 25 pediatric cases reported. Its concurrence with plastic bronchitis (PB) has not been well characterized, and host factors predisposing to recurrent infection-triggered hyperinflammation remain poorly understood.
Case presentation: A 6-year-old previously healthy girl experienced two hyperinflammatory episodes separated by 7 months. The first episode (August 2023) featured fever, lymphadenopathy, hepatosplenomegaly, hyperferritinemia (4,184 ng/mL), elevated cytokines, and declining blood counts but did not fulfill complete HLH-2004 criteria; it resolved with hepatoprotective therapy and a short corticosteroid course. The second episode (March 2024), triggered by confirmed M. pneumoniae infection (targeted next-generation sequencing), fulfilled 7 of 8 HLH-2004 criteria: fever, splenomegaly, pancytopenia (hemoglobin nadir 72 g/L, platelets 32 × 10 ⁹ /L, ANC 0.86 × 10 ⁹ /L), hypertriglyceridemia/hypofibrinogenemia (0.748 g/L), hyperferritinemia (31,905 ng/mL), decreased NK-cell activity, and bone marrow hemophagocytosis, with elevated soluble CD25 (9,249 pg/mL, approximately 2,312 U/mL—marginally below the 2,400 U/mL threshold but indicative of significant T-cell activation) and an HScore of 231 (>99% probability). Complications included severe hepatic injury (AST 4,017 U/L), consumptive coagulopathy, toxic–metabolic encephalopathy with seizure, and histologically confirmed type I plastic bronchitis requiring two bronchoscopies for bilateral cast extraction. Immunological evaluation revealed borderline NK-cell degranulation (ΔCD107a 5.68%; severe impairment threshold ≤5%) with normal CTL degranulation and preserved perforin, MUNC13-4, SAP, and XIAP expression. Quantitative NK-cell deficiency had been documented during the first episode. Treatment with modified HLH-2004 protocol (dexamethasone and IVIG without etoposide), doxycycline, and supportive care achieved complete recovery.
Conclusion: This case demonstrates that MP-HLH can present with exceptional severity including type I PB and multiorgan failure, particularly in children with prior hyperinflammatory episodes suggesting underlying immune vulnerability. Borderline NK-cell degranulation combined with quantitative NK-cell deficiency and recurrent hyperinflammation supports a threshold model of HLH susceptibility. Functional immune screening including CD107a degranulation assays should be performed in children with recurrent or unusually severe infection-triggered hyperinflammation, even without a definitive monogenic diagnosis.
Related
- Editorial: The expanding spectrum of hemophagocytic lymphohistiocytosis: pathogenic mechanisms and therapeutic implications
- Commentary: Hemophagocytic lymphohistiocytosis induced by immune checkpoint inhibitors: observations and proposed clinical management
- Case Report: Fulminant aggressive NK-cell leukemia with hemophagocytic lymphohistiocytosis and multiple organ dysfunction successfully bridged to allogeneic hematopoietic stem cell transplantation
- Kikuchi-Fujimoto disease with hemophagocytic lymphohistiocytosis in children: a seven-patient case series
- Emergence of Novel Macrolide-Resistant Mycoplasma pneumoniae Sequence Type 3 Subclades in Children after COVID-19 Pandemic, Taiwan
BibTeX
@article{zhang2026mycoplasma,
title = {{Mycoplasma pneumoniae-triggered hemophagocytic lymphohistiocytosis complicated by type I plastic bronchitis in a child: a case report}},
author = {Mengyao Zhang and Jiafeng Zheng and Caili Zhou and Yongsheng Xu},
journal = {Frontiers in Immunology},
year = {2026},
month = oct,
doi = {10.3389/fimmu.2026.1944516},
url = {https://www.frontiersin.org/articles/10.3389/fimmu.2026.1944516/full},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Mycoplasma pneumoniae-triggered hemophagocytic lymphohistiocytosis complicated by type I plastic bronchitis in a child: a case report
AU - Mengyao Zhang
AU - Jiafeng Zheng
AU - Caili Zhou
AU - Yongsheng Xu
PY - 2026
DA - 2026/10/29
JO - Frontiers in Immunology
DO - 10.3389/fimmu.2026.1944516
UR - https://www.frontiersin.org/articles/10.3389/fimmu.2026.1944516/full
AB - Background: Hemophagocytic lymphohistiocytosis (HLH) triggered by Mycoplasma pneumoniae (MP) is exceptionally rare in children, with fewer than 25 pediatric cases reported. Its concurrence with plastic bronchitis (PB) has not been well characterized, and host factors predisposing to recurrent infection-triggered hyperinflammation remain poorly understood. Case presentation: A 6-year-old previously healthy girl experienced two hyperinflammatory episodes separated by 7 months. The first episode (August 2023) featured fever, lymphadenopathy, hepatosplenomegaly, hyperferritinemia (4,184 ng/mL), elevated cytokines, and declining blood counts but did not fulfill complete HLH-2004 criteria; it resolved with hepatoprotective therapy and a short corticosteroid course. The second episode (March 2024), triggered by confirmed M. pneumoniae infection (targeted next-generation sequencing), fulfilled 7 of 8 HLH-2004 criteria: fever, splenomegaly, pancytopenia (hemoglobin nadir 72 g/L, platelets 32 × 10 ⁹ /L, ANC 0.86 × 10 ⁹ /L), hypertriglyceridemia/hypofibrinogenemia (0.748 g/L), hyperferritinemia (31,905 ng/mL), decreased NK-cell activity, and bone marrow hemophagocytosis, with elevated soluble CD25 (9,249 pg/mL, approximately 2,312 U/mL—marginally below the 2,400 U/mL threshold but indicative of significant T-cell activation) and an HScore of 231 (>99% probability). Complications included severe hepatic injury (AST 4,017 U/L), consumptive coagulopathy, toxic–metabolic encephalopathy with seizure, and histologically confirmed type I plastic bronchitis requiring two bronchoscopies for bilateral cast extraction. Immunological evaluation revealed borderline NK-cell degranulation (ΔCD107a 5.68%; severe impairment threshold ≤5%) with normal CTL degranulation and preserved perforin, MUNC13-4, SAP, and XIAP expression. Quantitative NK-cell deficiency had been documented during the first episode. Treatment with modified HLH-2004 protocol (dexamethasone and IVIG without etoposide), doxycycline, and supportive care achieved complete recovery. Conclusion: This case demonstrates that MP-HLH can present with exceptional severity including type I PB and multiorgan failure, particularly in children with prior hyperinflammatory episodes suggesting underlying immune vulnerability. Borderline NK-cell degranulation combined with quantitative NK-cell deficiency and recurrent hyperinflammation supports a threshold model of HLH susceptibility. Functional immune screening including CD107a degranulation assays should be performed in children with recurrent or unusually severe infection-triggered hyperinflammation, even without a definitive monogenic diagnosis.
SN - 1664-3224
ER -