Clinical practice recommendations for the diagnosis and management of human herpesvirus-6B encephalitis after allogeneic hematopoietic stem cell transplantation: the Japan Society for Hematopoietic Cell Transplantation

Distinguishing seizures in autoimmune limbic encephalitis from mesial temporal lobe epilepsy with hippocampal sclerosis: Clues of a temporal plus network

OBJECTIVE

Diagnosing autoimmune limbic encephalitis (ALE) in adults with new-onset seizures can be challenging, especially when seizures represent the predominant manifestation and MRI findings are not straightforward. By comparison with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), this study aimed to identify ictal electro-clinical features that might help clinicians recognize ALE-related seizures.

METHODS

This retrospective, multi-centre study analysed the ictal semiology and EEG correlate of 116 video-EEG-captured seizures in 40 ALE patients and 45 ones recorded in 21 MTLE-HS subjects. The proportion of patients presenting each clinical feature on at least one occasion was compared between the study groups. Latent class analysis (LCA) was also performed.

RESULTS

Ictal features were overall more numerous in ALE than in MTLE-HS (33 vs 22), and LCA confirmed the intrinsic variability of ALE-related seizures. Hyperventilation served as a trigger only in ALE (4/40). Awareness impairment (p = 0.032), limb dystonic posturing (p = 0.009) and manual automatisms (p < 0.001) were significantly less common in ALE cases. Conversely, piloerection was observed only in ALE subjects, although it did not reach statistical significance (p = 0.289), as was the case for déjà-vu (p = 0.084), and sensory symptoms (p = 0.079). Regarding EEG, the type of ictal pattern differed significantly (p = 0.007).

SIGNIFICANCE

This study shows that, despite the wide overlap with MTLE-HS, some ictal electro-clinical features could help clinicians suspect the autoimmune origin of adult-onset seizures. Moreover, autoimmune limbic seizures apparently shared similarities with 'temporal plus' epilepsy, which could partly account for the poor surgical outcomes and provide an interesting conceptual framework for future research.

A systematic review and meta-analysis of HHV-6 and mortality after hematopoietic cell transplant

Human herpesvirus-6B (HHV-6B) reactivation has been associated with non-relapse mortality (NRM) and overall mortality (OM) following allogeneic hematopoietic stem cell transplant (HCT). We performed a systematic review and meta-analysis to better quantify the association. Studies were included if they systematically tested a cohort of HCT recipients for HHV-6 infection or reactivation and described mortality for patients with and without HHV-6B. Random effects models were used to assess the pooled effect of HHV-6B positivity on each outcome of interest. Bayesian aggregation was additionally performed if models included 10 or fewer studies. Eight studies were included in the NRM analysis, which demonstrated a significant association between HHV-6 detection and NRM (pooled effect: 1.84; 95% CI: 1.29-2.62) without significant heterogeneity (I2 = 0.0%, p = 0.55). A Bayesian aggregation of the raw data used to construct the NRM random effects model supported these findings (95% credible interval: 0.15-1.13). Twenty-five studies were included in OM analysis, which showed a significant positive association (pooled effect: 1.37; 95% CI: 1.07-1.76), though considerable heterogeneity was observed (I2 = 36.7%, p < 0.05). HHV-6 detection is associated with NRM and OM following HCT. Randomized trials are warranted to evaluate if preventing or treating HHV-6B reactivation improves outcomes.

Outcomes of Haploidentical Stem Cell Transplant Recipients With HHV-6B Reactivation

Background

Human herpesvirus 6B (HHV-6B) frequently reactivates following allogeneic stem cell transplant (alloHCT). Consensus guidelines note that haploidentical alloHCT may represent a high-risk population for which there is little evidence; this warrants further investigation.

Methods

In this single-center retrospective study, we evaluated 188 consecutive adult patients receiving haploidentical alloHCT between 11/2014 and 11/2020 and compared outcomes between patients with HHV-6B reactivation receiving targeted antiviral therapy and those who were clinically observed.

Results

Of the 58 included patients, 21 (36.2%) received antiviral therapy for HHV-6B reactivation with foscarnet (n = 19) or ganciclovir (n = 2). There were no differences in patient or disease characteristics between treated and observed patients. Treated patients were more likely to have high-level DNAemia (85.7% vs 40.5%; P < .001) and had higher peak viral quantitative measurements (median log10, 4.65 vs 3.84; P < .001). The median time to clearance from plasma (interquartile range) was 13 (7.25-20.00) days for all patients and was not significantly different between groups. There were no differences in episodes of encephalitis, grade III/IV acute graft-vs-host disease (GVHD), or time to neutrophil or platelet engraftment among treated vs observed patients. Day 100 nonrelapse mortality was not significantly different in the multivariate analysis; however, the presence of central nervous system symptoms was strongly associated with worse survival (hazard ratio, 4.11; 95% CI, 1.27-13.34; P = .018).

Conclusions

We did not observe a difference in clinical outcomes between the treated and observed groups of patients with HHV-6B reactivation following haploidentical alloHCT. With the rising use of haploidentical transplant and post-transplant cyclophosphamide GVHD prevention platforms, prospective studies are needed to further characterize the risk and outcomes associated with HHV-6B reactivation and therapy.

Human herpesvirus-6, HHV-8 and parvovirus B19 after allogeneic hematopoietic cell transplant: the lesser-known viral complications

PURPOSE OF REVIEW

Viral infections continue to burden allogeneic hematopoietic cell transplant (HCT) recipients. We review the epidemiology, diagnosis, and management of human herpesvirus (HHV)-6, HHV-8 and parvovirus B19 following HCT.

RECENT FINDINGS

Advances in HCT practices significantly improved outcomes but impact viral epidemiology: post-transplant cyclophosphamide for graft-versus-host disease prevention increases HHV-6 reactivation risk while the impact of letermovir for CMV prophylaxis - and resulting decrease in broad-spectrum antivirals - is more complex. Beyond the well established HHV-6 encephalitis, recent evidence implicates HHV-6 in pneumonitis. Novel less toxic therapeutic approaches (brincidofovir, virus-specific T-cells) may enable preventive strategies in the future. HHV-8 is the causal agent of Kaposi's sarcoma, which is only sporadically reported after HCT, but other manifestations are possible and not well elucidated. Parvovirus B19 can cause severe disease post-HCT, frequently manifesting with anemia, but can also be easily overlooked due to lack of routine screening and ambiguity of manifestations.

SUMMARY

Studies should establish the contemporary epidemiology of HHV-6, and other more insidious viruses, such as HHV-8 and parvovirus B19 following HCT and should encompass novel cellular therapies. Standardized and readily available diagnostic methods are key to elucidate epidemiology and optimize preventive and therapeutic strategies to mitigate the burden of infection.

Human Herpes Virus-6 (HHV-6) Reactivation after Hematopoietic Cell Transplant and Chimeric Antigen Receptor (CAR)- T Cell Therapy: A Shifting Landscape

HHV-6B reactivation affects approximately half of all allogeneic hematopoietic cell transplant (HCT) recipients. HHV-6B is the most frequent infectious cause of encephalitis following HCT and is associated with pleiotropic manifestations in this setting, including graft-versus-host disease, myelosuppression, pneumonitis, and CMV reactivation, although the causal link is not always clear. When the virus inserts its genome in chromosomes of germ cells, the chromosomally integrated form (ciHHV6) is inherited by offspring. The condition of ciHHV6 is characterized by the persistent detection of HHV-6 DNA, often confounding diagnosis of reactivation and disease-this has also been associated with adverse outcomes. Recent changes in clinical practice in the field of cellular therapies, including a wider use of post-HCT cyclophosphamide, the advent of letermovir for CMV prophylaxis, and the rapid expansion of novel cellular therapies require contemporary epidemiological studies to determine the pathogenic role and spectrum of disease of HHV-6B in the current era. Research into the epidemiology and clinical significance of HHV-6B in chimeric antigen receptor T cell (CAR-T cell) therapy recipients is in its infancy. No controlled trials have determined the optimal treatment for HHV-6B. Treatment is reserved for end-organ disease, and the choice of antiviral agent is influenced by expected toxicities. Virus-specific T cells may provide a novel, less toxic therapeutic modality but is more logistically challenging. Preventive strategies are hindered by the high toxicity of current antivirals. Ongoing study is needed to keep up with the evolving epidemiology and impact of HHV-6 in diverse and expanding immunocompromised patient populations.

Differential clinical impact of letermovir prophylaxis according to graft sources: a KSGCT multicenter retrospective analysis

ABSTRACT

Clinically significant cytomegalovirus infection (csCMVi) is frequently observed after allogeneic hematopoietic stem cell transplantation (HSCT) and prophylaxis with letermovir is commonly adopted. However, the clinical benefit of letermovir prophylaxis according to graft sources has not been sufficiently elucidated. We retrospectively analyzed 2194 recipients of HSCT who were CMV-seropositive (236 with letermovir prophylaxis and 1958 without prophylaxis against CMV). csCMVi was significantly less frequent in patients with letermovir prophylaxis than in those without (23.7% vs 58.7% at 100 days after HSCT, P < .001) and the same trend was seen when recipients of bone marrow (BM), peripheral blood stem cell (PBSC), or cord blood (CB) transplantation were separately analyzed. In recipients of BM, nonrelapse mortality (NRM) was significantly lower in the letermovir group at 6 months after HSCT (5.0% vs 14.9%, P = .018), and the same trend was observed in recipients of PBSCs (14.7% vs 24.8%, P = .062); however, there was no statistical significance at 1 year (BM, 21.1% vs 30.4%, P = .67; PBSCs, 21.2% vs 30.4%, P = .096). In contrast, NRM was comparable between recipients of CB with and without letermovir prophylaxis throughout the clinical course (6 months, 23.6% vs 24.3%, P =.92; 1 year, 29.3% vs 31.0%, P = .77), which was confirmed by multivariate analyses. In conclusion, the impact of letermovir prophylaxis on NRM and csCMVi should be separately considered according to graft sources.

Hematopoietic stem cell transplantation and the noncytomegalovirus herpesviruses

Although hematopoietic stem cell transplantation (HSCT) and other cellular therapies have significantly improved outcomes in the management of multiple hematological and nonhematological malignancies, the resulting impairment in humoral and cellular response increases the risk for opportunistic infection as an undesirable side effect. With their ability to establish latent infection and reactivate when the host immune system is at its weakest point, the Herpesviridae family constitutes a significant proportion of these opportunistic pathogens. Despite recent advancements in preventing and managing herpesvirus infections, they continue to be a common cause of significant morbidity and mortality in transplanted patients. Herein, we aim to provide and update on herpesvirus other than cytomegalovirus (CMV) affecting recipients of HSCT and other cellular therapies.

Impact of Antimicrobial Drug-Drug Interactions on Acute Kidney Injury after Allogeneic Hematopoietic Cell Transplantation

Acute kidney injury (AKI) is one of the major complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The use of multiple antimicrobials is one of the major causes of post-transplantation AKI, owing to the potential nephrotoxicity of each agent and of drug-drug interactions (DDIs). No satisfactory reports on DDIs the field of allo-HSCT have been published. We performed a retrospective analysis to compare the incidence of AKI within 100 days post-transplantation. A total of 465 allo-HSCTs in 416 patients were analyzed, and the cumulative incidence of AKI was 40.0%. AKI was associated with significantly reduced overall survival (hazard ratio [HR], 2.66; 95% confidence interval [CI] 1.95 to 3.55; P < .01) and increased transplantation-related mortality (HR, 4.77, 95% CI, 2.90 to 7.88; P < .01). A higher incidence of AKI was significantly associated with the use of ciprofloxacin, cefepime, tazobactam/piperacillin, meropenem, vancomycin, liposomal amphotericin B, ganciclovir, and foscarnet. Among these drugs, combinations of vancomycin plus tazobactam/piperacillin (HR, 2.23; P = .09 for interaction), ganciclovir plus cefepime (HR, 5.93; P = .04), and ganciclovir plus meropenem (HR, 2.63; P = .12) synergistically increased the risk of AKI, whereas combinations involving teicoplanin did not. This is the first report dealing with DDIs after allo-HSCT, indicating that such combinations should be avoided to preserve renal function and reduce AKI-related morbidity and mortality.

Evaluation of an automated system for the quantitation of human Herpesvirus-6 DNA from clinical specimens

Background

Quantitation of human herpesvirus-6 (HHV-6) DNA in clinical specimens is important for the diagnosis and management of HHV-6-associated infection and reactivation in immunocompromised patients, particularly transplant recipients.

Methods

The analytical performance of the Altona RealStar ASR HHV-6 qPCR on the semi-automated AltoStar AM16 system was assessed using HHV-6 reference material in plasma and cerebral spinal fluid (CSF). Qualitative and quantitative agreement was determined using 123 clinical EDTA plasma specimens tested using a laboratory-developed HHV-6 qPCR.

Results

The 95% Lower Limit of Detection was 20 IU/mL [95% confidence interval (CI): 10 to 29] in plasma and 78 IU/mL (95% CI: 55 to 146) in CSF. The assay was linear from 7.0 to 2.0 log10 IU/mL in both matrices. Overall agreement of the RealStar ASR HHV-6 qPCR on the AltoStar AM16 with a laboratory-developed test was 95.9% (95% CI: 90.8 to 98.7). Passing-Bablok analysis of specimens quantifiable by both methods and at levels >1000 copies/mL revealed a regression line of Y = 1.00*X-0.20, with neither systematic (95% CI Y-intercept: -0.66 to 0.26) nor proportional (95% CI slope: 0.89 to 1.10) bias compared to the reference.

Conclusions

The RealStar ASR HHV-6 qPCR on the AltoStar AM16 provides accurate quantitation for clinical monitoring of HHV-6 in immunocompromised hosts.

Current Perspectives on the Management of Herpesvirus Infections in Solid Organ Transplant Recipients

Solid organ transplant recipients (SOTRs) are at high risk of human herpesvirus (HHV)-related morbidity and mortality due to the use of immunosuppressive therapy. We aim to increase awareness and understanding of HHV disease burden in SOTRs by providing an overview of current prevention and management strategies as described in the literature and guidelines. We discuss challenges in both prevention and treatment as well as future perspectives.

Once Daily Foscarnet is Effective for HHV-6 Reactivation after Hematopoietic Stem Cell Transplantation

BACKGROUND

Human herpesvirus 6 (HHV-6) reactivation is common after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is associated with higher mortality and transplant-related complications.

OBJECTIVES

We hypothesized that preemptive treatment with short course of foscarnet at lower cut point of plasma HHV-6 viral load would be effective in treating early HHV-6 reactivation, prevent complications and hospitalization of these patients.

METHODS

We reviewed outcomes of adult patients (18 years or older) who received preemptive treatment with once daily foscarnet 60-90 mg/kg for 7 days for HHV-6 reactivation after allo-HSCT at our institution between 05/2020-11/2022. Plasma HHV-6 viral load was monitored using quantitative polymerase chain reaction twice monthly in the first 100 days post-transplant and twice weekly after reactivation until resolution.

RESULTS

Eleven patients with a median age of 46 years (range, 23-73) were included in the analysis. Ten patients received HSCT from a haploidentical and one patient from HLA matched related donor. The most common diagnosis was acute leukemia (9 cases). Myeloablative- and reduced-intensity conditioning regimens were used in 4 cases and 7 cases, respectively. Most patients (10/11) received post-transplantation cyclophosphamide-based graft-versus-host disease prophylaxis. Median follow-up was 440 days (range, 174-831). Median time to HHV-6 reactivation was 22 days post-transplantation (range, 15-89), median level of viral load 3,100 copies/mL (range, 210-118,000) at first reactivation and median peak viral load was 11,300 copies/mL (range, 600-983,000). All patients received a short course of foscarnet of 90 mg/kg/day (N=7) and 60 mg/kg/day (N=4). Plasma HHV-6 DNA in all patients became undetected after completion of one week treatment. No HHV-6 encephalitis or pneumonitis occurred. All patients achieved neutrophil and platelet engraftment after a median time of 16 (range, 8-22) and 26 (range, 14-168) days, respectively, with no secondary graft failure. No complications related to foscarnet administration were noted. One patient with very high HHV-6 viremia had recurrent reactivation and received a second course of foscarnet as outpatient.

CONCLUSIONS

Short course of once daily foscarnet is effective in treating early HHV-6 reactivation post-transplant, may reduce incidence of HHV-6-related and treatment-related complications, and prevent hospitalization in these patients.

Intracerebral opportunistic infections caused by immunosuppressants after orthotopic liver transplantation: Report of two cases and literature review

Central nervous system (CNS) infections in adults are rare because of normal immunity and the existence of the blood brain barrier, which prevents the invasion of pathogenic microorganisms. Liver transplant recipients are at an increased risk of opportunistic infections (OI) due to immunosuppressive therapy compared to those with normal immunity. Early diagnosis and timely implementation of treatment are critical for the successful treatment of these infections. We present two cases of intracerebral OI after orthotopic liver transplantation (OLT), with different clinical presentations. Patient 1 presented with epileptic seizures, mainly manifested as unresponsiveness, unconsciousness, and coma complicated with involuntary limb twitching. Patient 2 presented with a consciousness disorder, mainly manifested as unclear consciousness content, poor orientation, calculation power, and logical ability. Next-generation sequencing (NGS) examination of the cerebrospinal fluid confirmed human herpesvirus 6 B (HHV-6B) infection in patient 1 and intracranial Aspergillus infection in patient 2. Intracranial OI has insidious onset and atypical clinical manifestations. NGS can allow for the proper diagnosis and monitoring of the effects of treatment.

Current Role of Prospective Monitoring, Pre-emptive and Prophylactic Therapy for Human Herpesvirus-6 after Allogeneic Stem Cell Transplantation

Human herpesvirus 6 (HHV-6) frequently reactivates after allogeneic stem cell transplantation (SCT). Most patients are asymptomatic and viremia often resolves without therapy; however, transplant-related complications may be associated with reactivation. Multiple presentations have been attributed to HHV-6 reactivation after SCT including encephalitis. Several strategies have been trialed to reduce such risks or complications. Challenges exist with prospective monitoring strategies, and established thresholds of high-level reactivation may be limited. Three published guidelines and extensive trials focusing on preemptive and prophylactic strategies are reviewed. Future areas of investigation and high-risk populations are described. Existing trials and testing platforms have significant limitations, and to date no clear benefit for a preemptive or prophylactic intervention has been demonstrated.

HLA 1-3 antigen-mismatched related peripheral blood stem cells transplantation using low-dose antithymocyte globulin versus unrelated cord blood transplantation

Little information is available regarding whether unrelated cord blood transplantation (CBT) or an HLA 1-3 antigen-mismatched related donor peripheral blood stem-cell transplantation (PBSCT) using low-dose anti-thymocyte globulin (ATG) is superior as an alternative transplantation for patients who lack an HLA-matched sibling or unrelated donor. Therefore, we evaluated 7861 patients with hematologic malignancies (aged 0 to 70 years) who received either a CBT without ATG (CBT-no ATG, n = 7034) or an HLA 1-3 antigen-mismatched related donor PBSCT using low-dose ATG (PBSCT-ATG, n = 827). CBT-no ATG was associated with significantly better overall survival (OS) than the use of a PBSCT-ATG (hazard ratio [HR], 0.77; p < .001), although PBSCT-ATG patients with an HLA 1 antigen-mismatch showed OS comparable to that in the CBT-no ATG group. Neutrophil and platelet engraftment was significantly delayed, whereas the incidences of nonrelapse mortality, and severe graft-versus-host disease (GVHD) were significantly lower in the CBT-no ATG group. The incidences of relapse and chronic GVHD were comparable between these donors. In conclusion, CBT-no ATG may be a better alternative than HLA-mismatched related donor PBSCT using low-dose ATG. Notably, HLA 2-3 antigen mismatch-related transplantation with low-dose ATG had significant adverse effects on transplantation outcomes.

Unique Challenges to Diagnosing Human Herpesvirus-6 (HHV-6) Encephalitis Following Post-Hematopoietic Stem Cell Transplant: A Case and Brief Review

A patient with an ultimate diagnosis of human herpesvirus-6 (HHV-6) encephalitis developed central nervous system (CNS) symptoms 13 days after undergoing myeloablative haploidentical allogeneic hematopoietic stem cell transplant (HSCT). Due to the patient's body habitus, magnetic resonance (MR) imaging was not obtained until the onset of retrograde amnesia on day +24. MR imaging and other clinical findings eliminated all skepticism of HHV-6 encephalitis and HHV-6 antivirals were initiated on day +28, leading to gradual recovery. This case demonstrates some of the factors that may complicate the diagnosis of post-alloHSCT HHV-6 encephalitis. Because HHV-6 encephalitis and viremia can occur without warning, a single negative study should not exclude future development, especially if CNS symptoms are present. Acute graft-versus-host disease and cord blood transplantation are both significant risk factors for HHV-6 encephalitis. Human leukocyte antigen (HLA) mismatch, engraftment complications, or certain HLA alleles have also been associated with HHV-6 encephalitis. Chromosomally integrated HHV-6 must also be ruled out to prevent inappropriate and potentially harmful administration of antivirals. Due to the severe short- and long-term sequelae of HHV-6 encephalitis, appropriate treatment should be administered as soon as possible.

HHV-6 Encephalitis After Chimeric Antigen Receptor T-cell Therapy (CAR-T): 2 Case Reports and a Brief Review of the Literature

Human herpesvirus 6 (HHV-6) reactivation can occur in patients who are highly immunosuppressed, including those who have undergone hematopoietic stem cell transplantation (HSCT). HHV-6 encephalitis is a severe manifestation that is well described in the HSCT population. Chimeric antigen receptor T-cell (CAR-T) therapy is a novel cancer-directed immunotherapy that results in severe immunosuppression. Patients undergoing CAR-T therapy may be at risk for HHV-6 encephalitis, which can be difficult to distinguish from a common adverse effect of CAR-T therapy, neurotoxicity. Herein, we describe 2 patients diagnosed with HHV-6 encephalitis after CAR-T therapy and discuss the diagnostic approach and differential diagnosis for altered mental status after CAR-T therapy. Diagnosing HHV-6 encephalitis can be difficult in this patient population as altered mental status is common after CAR-T therapy and may be attributed to CAR-T-associated neurotoxicity.

Kinetics and clinical significance of human herpesvirus 6 DNA shedding in saliva after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Little is known about the kinetics and clinical significance of saliva human herpesvirus-6 (HHV-6) DNA after hematopoietic stem cell transplantation (HSCT).

METHODS

In this observational study, we quantified HHV-6 DNA in serially collected plasma and saliva from allogeneic HSCT recipients. Associations between the status of salivary HHV-6 DNA and the development of HHV-6 encephalitis, depression, and oral mucosal graft-versus-host disease (GVHD) were retrospectively analyzed.

RESULTS

A total of 787 plasma and 434 saliva samples were collected from 56 patients. The cumulative incidence of HHV-6 DNA in plasma and saliva at 60 days after transplantation was 51.8% and 83.9%, respectively. The peak level of salivary HHV-6 DNA was significantly higher in patients who displayed plasma HHV-6 DNA than in those who did not (median, 51,584 copies/mL vs 587 copies/mL; P < .0001). Salivary HHV-6 DNA levels increased after positive plasma HHV-6 DNA was detected and remained high during observation period. Despite the frequent occurrence of positive salivary HHV-6 DNA, no patient developed depression. Positivity of salivary HHV-6 DNA was not significantly associated with the development of HHV-6 encephalitis (P = 1.00, Fisher's exact test) or oral mucosal GVHD (P = .71, Grey's test). No significant relationship between salivary HHV-6 DNA and these diseases was found even when comparing higher HHV-6 DNA loads in saliva.

CONCLUSION

Salivary HHV-6 DNA levels increased after HHV-6 DNA was detected in the blood. However, no epidemiological evidence was shown to support a role of salivary HHV-6 in the development of HHV-6 encephalitis, depression, and oral mucosal GVHD.

Retrospective case analysis of antiviral therapies for HHV-6 encephalitis after hematopoietic stem cell transplantation

Human herpesvirus 6 (HHV-6) is one of the most common causes of encephalitis in allogeneic hematopoietic stem cell transplant (HCT) recipients and is associated with significant morbidity and mortality. There are no FDA-approved treatments specifically for HHV-6 encephalitis; HHV-6 disease is typically treated with CMV antivirals. A review of antiviral medications used to treat HHV-6 encephalitis was conducted by aggregating data from case reports found on PubMed. Articles were included if they examined at least one HCT patient diagnosed with HHV-6 encephalitis and described their treatment course and outcome. Key data were abstracted from 123 cases described in 52 studies. The proportion of patients with encephalitis who died or developed sequelae was 63.6% among ganciclovir monotherapy recipients (n = 44), 55.3% among foscarnet monotherapy recipients (n = 47), and 37.5% among recipients of combination therapy with foscarnet and ganciclovir (n = 32). Logistic regression revealed that recipients of foscarnet (OR 4.286, 95% CI 1.235-14.877, P = .022) and ganciclovir (OR 5.625, 95% CI 1.584-19.975, P = .008) monotherapies were more likely to develop sequelae compared to recipients of combination therapy, respectively. In multivariate analyses, non-cord blood transplant was identified as an independent risk factor for developing sequelae after receiving ganciclovir monotherapy (OR 5.999, 95% CI 1.274-28.254, P = .023). There was no difference in mortality between patients who received combination therapy and those who received monotherapy. In conclusion, combination therapy with foscarnet and ganciclovir may reduce sequelae, but not mortality, secondary to HHV-6 encephalitis.