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Peer-reviewedCC BY-NC-ND 4.0The American Journal of Case Reports

HHV-6 Encephalitis Presenting With Severe SIADH and CO2 Narcosis in Non-Transplant Smoldering Adult T-Cell Leukemia/Lymphoma

  • Kana Tateishi1
  • Toyoshi Yanagihara1
  • Ryoma Kawabata1
  • Eriko Kinoshita1
  • Takeshi Miyazaki2
  • Yuji Tateishi2
  • Kaori Koga3
  • Makoto Hamasaki3
  • Masaki Fujita1
  1. 1Department of Respiratory Medicine, Fukuoka University Hospital, Fukuoka, Japan
  2. 2Department of Neurology, Fukuoka University Hospital, Fukuoka, Japan
  3. 3Department of Pathology, Fukuoka University Hospital, Fukuoka, Japan
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Abstract

Patient: Female, 55-year-old

Final Diagnosis: HHV-6 encephalitis

Symptoms: Impaired consciousness • nausea

Clinical Procedure: Bronchoscopy • lumbar puncture

Specialty: Hematology • Infectious Diseases • Neurology

Objective: Rare coexistence of disease or pathology

Background: Human herpesvirus 6 (HHV-6) encephalitis is best recognized after allogeneic hematopoietic stem cell transplantation but can also occur in non-transplant immunocompromised patients. Hyponatremia and syndrome of inappropriate antidiuretic hormone secretion (SIADH) may precede or accompany HHV-6 encephalitis. Severe SIADH as an early dominant clue in non-transplant patients with smoldering adult T-cell leukemia/lymphoma (ATLL) is not fully described.

Case Report: A 55-year-old woman with smoldering ATLL received systemic corticosteroid therapy for clinically diagnosed human T-cell leukemia virus type 1 (HTLV-1)-associated uveitis and was admitted for progressive pulmonary infection. Bronchoscopic specimens revealed polymicrobial infection, including Nocardia and Actinomyces; invasive pulmonary aspergillosis was also clinically suspected. Although pulmonary findings improved with antimicrobial and antifungal therapy, she developed nausea, acute impairment of consciousness, and severe SIADH-associated hyponatremia. Serum sodium decreased to 113 mmol/L, and consciousness did not adequately improve after sodium correction. Cerebrospinal fluid obtained by lumbar puncture on hospital day 13 showed HHV-6 DNA positivity (1.0 × 103 copies/mL). Brain magnetic resonance imaging demonstrated bilateral cortical and limbic abnormalities, supporting a clinical diagnosis of HHV-6 encephalitis. Ganciclovir was initiated on hospital day 15 along with sodium correction, tolvaptan, and supportive care. The patient subsequently developed hypercapnic respiratory failure and CO2 narcosis requiring mechanical ventilation. Her neurologic and respiratory status gradually improved, and she was discharged on hospital day 53.

Conclusions: In non-transplant patients with ATLL, corticosteroid exposure, and opportunistic infection, severe SIADH accompanied by new neurologic symptoms can be an early clue to HHV-6 encephalitis. Early recognition and prompt initiation of antiviral therapy may help to improve neurologic outcomes.

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Cite

BibTeXRIS
BibTeX
@article{tateishi2026hhv6,
  title = {{HHV-6 Encephalitis Presenting With Severe SIADH and CO2 Narcosis in Non-Transplant Smoldering Adult T-Cell Leukemia/Lymphoma}},
  author = {Kana Tateishi and Toyoshi Yanagihara and Ryoma Kawabata and Eriko Kinoshita and Takeshi Miyazaki and Yuji Tateishi and Kaori Koga and Makoto Hamasaki and Masaki Fujita},
  journal = {The American Journal of Case Reports},
  year = {2026},
  month = oct,
  doi = {10.12659/ajcr.954380},
  url = {https://doi.org/10.12659/ajcr.954380},
  note = {CC BY-NC-ND 4.0},
}
RIS
TY  - JOUR
TI  - HHV-6 Encephalitis Presenting With Severe SIADH and CO2 Narcosis in Non-Transplant Smoldering Adult T-Cell Leukemia/Lymphoma
AU  - Kana Tateishi
AU  - Toyoshi Yanagihara
AU  - Ryoma Kawabata
AU  - Eriko Kinoshita
AU  - Takeshi Miyazaki
AU  - Yuji Tateishi
AU  - Kaori Koga
AU  - Makoto Hamasaki
AU  - Masaki Fujita
PY  - 2026
DA  - 2026/10/28
JO  - The American Journal of Case Reports
DO  - 10.12659/ajcr.954380
UR  - https://doi.org/10.12659/ajcr.954380
AB  - Patient: Female, 55-year-old  Final Diagnosis: HHV-6 encephalitis  Symptoms: Impaired consciousness • nausea  Clinical Procedure: Bronchoscopy • lumbar puncture  Specialty: Hematology • Infectious Diseases • Neurology  Objective: Rare coexistence of disease or pathology  Background: Human herpesvirus 6 (HHV-6) encephalitis is best recognized after allogeneic hematopoietic stem cell transplantation but can also occur in non-transplant immunocompromised patients. Hyponatremia and syndrome of inappropriate antidiuretic hormone secretion (SIADH) may precede or accompany HHV-6 encephalitis. Severe SIADH as an early dominant clue in non-transplant patients with smoldering adult T-cell leukemia/lymphoma (ATLL) is not fully described.  Case Report: A 55-year-old woman with smoldering ATLL received systemic corticosteroid therapy for clinically diagnosed human T-cell leukemia virus type 1 (HTLV-1)-associated uveitis and was admitted for progressive pulmonary infection. Bronchoscopic specimens revealed polymicrobial infection, including Nocardia and Actinomyces; invasive pulmonary aspergillosis was also clinically suspected. Although pulmonary findings improved with antimicrobial and antifungal therapy, she developed nausea, acute impairment of consciousness, and severe SIADH-associated hyponatremia. Serum sodium decreased to 113 mmol/L, and consciousness did not adequately improve after sodium correction. Cerebrospinal fluid obtained by lumbar puncture on hospital day 13 showed HHV-6 DNA positivity (1.0 × 103 copies/mL). Brain magnetic resonance imaging demonstrated bilateral cortical and limbic abnormalities, supporting a clinical diagnosis of HHV-6 encephalitis. Ganciclovir was initiated on hospital day 15 along with sodium correction, tolvaptan, and supportive care. The patient subsequently developed hypercapnic respiratory failure and CO2 narcosis requiring mechanical ventilation. Her neurologic and respiratory status gradually improved, and she was discharged on hospital day 53.  Conclusions: In non-transplant patients with ATLL, corticosteroid exposure, and opportunistic infection, severe SIADH accompanied by new neurologic symptoms can be an early clue to HHV-6 encephalitis. Early recognition and prompt initiation of antiviral therapy may help to improve neurologic outcomes.
SN  - 1941-5923
ER  -