Hyperammonemic encephalopathy is a rapidly progressive neurotoxic syndrome caused by the accumulation of ammonia in the bloodstream. Ammonia, a byproduct of protein metabolism, is typically cleared efficiently by the liver. However, disruptions in its clearance can lead to elevated systemic concentrations, which readily cross the blood-brain barrier, disrupting neurotransmission and cellular metabolism within the central nervous system. This results in acute symptoms such as confusion, disorientation, lethargy, and potentially coma. While this syndrome is often associated with hepatic failure or inborn metabolic disorders, the case presented identifies 5-FU as a precipitating factor in a patient without evident hepatic impairment.

The patient in question was a 63-year-old woman undergoing chemotherapy for pancreatic cancer. Her treatment regimen included 5-FU in combination with other agents. Following multiple cycles, the patient experienced recurrent episodes of confusion and decreased consciousness. Intriguingly, despite comprehensive laboratory workups revealing normal liver enzyme levels and biochemistry, serum ammonia concentrations were found to be significantly elevated during the symptomatic episodes. This dissociation between liver function and ammonia elevation is particularly noteworthy and suggests a direct or indirect impairment of ammonia metabolism induced by 5-FU.

Mechanistically, 5-FU is a fluorinated pyrimidine analog widely utilized in oncology for gastrointestinal and various solid tumors. Beyond its cytotoxic effects targeting DNA synthesis, 5-FU may disrupt hepatic energy metabolism and enzyme systems critical for ammonia clearance, such as the urea cycle. This interference can impair the detoxification pathways, allowing systemic ammonia accumulation. Moreover, 5-FU metabolites may exert mitochondrial toxicity leading to altered hepatocyte function and further compromise of nitrogen clearance. This case underscores the complexity of 5-FU-induced toxicities, extending beyond classical myelosuppression and mucositis into metabolic and neurologic domains.

The diagnosis of 5-FU-induced hyperammonemic encephalopathy was further supported by employing the Naranjo adverse drug reaction probability scale, a validated tool used to assess the likelihood of drug-related adverse events. The temporal association between each 5-FU administration and the onset of neurological symptoms, followed by resolution after drug withdrawal and supportive therapy, strongly implicated 5-FU as the causative agent. Importantly, other medications, including antiepileptics and irinotecan, which the patient was also receiving and are known to be associated with hyperammonemia, were ruled out based on symptom patterns and response.

Therapeutic intervention focused on prompt discontinuation of 5-FU alongside administration of lactulose and intravenous fluids aimed at reducing systemic ammonia levels and supporting hepatic clearance mechanisms. Lactulose, a non-absorbable disaccharide, acidifies the gut lumen, promoting trapping of ammonia in its ionized form and enhancing fecal nitrogen excretion. This combined approach led to rapid neurological improvement and full resolution of the encephalopathy, confirming the diagnosis and reinforcing the reversibility of this drug-induced toxicity if promptly identified.

This case shines a spotlight on the necessity for oncologists and healthcare professionals to maintain a high index of suspicion for hyperammonemic encephalopathy in patients receiving 5-FU, particularly when new neurological symptoms arise. Routine liver function tests may not sufficiently predict or detect this complication, thus advocating for timely serum ammonia measurements in relevant clinical contexts. Early recognition and treatment are crucial to prevent potentially irreversible neurological damage or fatal outcomes.

Furthermore, these findings raise important considerations regarding the reintroduction of 5-FU in patients who have experienced hyperammonemia. The authors recommend cautious deliberation and consultation with specialists in metabolic disorders or clinical toxicology when considering rechallenge, as recurrence can be life-threatening. Alternative chemotherapeutic regimens or supportive care may be warranted to balance oncologic efficacy with patient safety.

In the broader context of cancer pharmacotherapy, this report expands understanding of 5-FU’s toxicity profile, emphasizing that adverse effects extend beyond conventional cytotoxicity to include metabolic dysfunction and neurotoxicity. It signals a pressing need for further research into the mechanisms by which 5-FU alters ammonia metabolism and for developing predictive biomarkers to identify susceptible individuals. The case also encourages exploration of prophylactic or adjunctive strategies to mitigate hyperammonemia risk during 5-FU treatment.

As cancer treatment protocols continue to evolve towards personalized medicine, the identification and management of rare but severe adverse events like 5-FU-induced hyperammonemic encephalopathy become paramount. Clinicians are urged to adopt a multidisciplinary approach encompassing oncology, neurology, hepatology, and pharmacology to optimize therapeutic outcomes and minimize toxicity. Patient education regarding early symptom reporting and monitoring for subtle neurocognitive changes is equally vital.

In light of this novel report, professional societies and guideline committees may consider incorporating recommendations for ammonia monitoring in specific clinical scenarios involving 5-FU. The clinical community is reminded that vigilance for silent toxicities—those not immediately evident through standard laboratory parameters—is essential to enhance patient safety and treatment success. This case exemplifies how rare adverse reactions can reveal critical insights into drug mechanisms, ultimately guiding improved cancer care.

The contribution by Kalfoutzou et al. opens an important dialogue in oncology and toxicology fields. By disseminating such findings in an open-access platform, the authors facilitate rapid knowledge translation to the global medical community. This transparency and accessibility are crucial in accelerating awareness, research, and clinical adaptation to safeguard patients undergoing chemotherapy worldwide.

Subject of Research: People
Article Title: Silent toxicity: A rare case of 5-fluorouracil-induced hyperammonemic encephalopathy
News Publication Date: December 23, 2025
Web References: http://dx.doi.org/10.18632/oncoscience.638
Image Credits: Copyright © 2025 Kalfoutzou et al. Licensed under CC BY 4.0
Keywords: oncology, hyperammonemia, encephalopathy, fluorouracil, neurotoxicity

The lead investigator, Dr. Peter E. Westerweel from the Albert Schweitzer Hospital in Dordrecht, The Netherlands, highlights the significance of their findings. His team revealed that digital PCR technology had a remarkable sensitivity rate of 97% in identifying the BCR::ABL1 transcript among patients who were considered to be in deep molecular remission. Remarkably, the molecular target was identified in two-thirds of patients whose levels were undetectable by the currently standard RT-qPCR method. This enhanced sensitivity provided a more reliable means of selecting candidates for discontinuation of tyrosine kinase inhibitors (TKIs), the current mainstay of treatment for CML.

Chronic myeloid leukemia, a type of cancer that affects the blood and bone marrow, is defined by the presence of the BCR::ABL1 fusion protein formed when the BCR and ABL1 genes fuse abnormally. Thanks to targeted therapies, particularly TKIs, many patients achieve deep molecular responses, significantly improving their prognosis. Some of these patients can reach a state of remission equivalent to that of the general population, and for them, the prospect of halting medication becomes a tantalizing possibility.

Within the framework of a nationwide multicenter study in the Netherlands, researchers collected blood samples from patients who were being evaluated for potential TKI discontinuation between July 2020 and May 2023. A total of 168 samples from 136 CML patients, gathered from 31 medical centers, provided critical data for this important study.

The use of digital PCR in quantifying the BCR::ABL1 levels on the International Scale yielded impressive results, detecting residual disease levels as low as 0.0023%. This precise cutoff point is essential for assessing treatment-free remission for patients. The goal of achieving a molecular response at the MR5.0 level involves the proficient detection of one BCR::ABL1 transcript amid a pool of at least 100,000 regular genetic copies, a benchmark met by the digital PCR technology in an impressive 97% of samples tested.

Furthermore, variations were observed among the patients concerning the fluorescence levels of droplets produced by the digital PCR technique. These differences arose due to the diverse types of BCR::ABL1 transcripts present in individual patients. Higher fluorescence in droplets signifies the presence of target transcripts, whereas lower fluorescence indicates a negative result. Understanding these nuances allows clinicians to discern which transcript type a patient has, an additional layer of information that was often unspecified before this study.

The two main transcript types identified – e13a2 and e14a2 – relate to different genetic rearrangements affecting treatment outcomes. Dr. Westerweel pointed out that the transcript types themselves have critical implications, as previous studies established them as risk factors for molecular relapse after the discontinuation of therapy. Given that the transcript type was typically unknown when patients reached deep remission, this innovative application of digital PCR offers significant potential for personalized medicine in CML treatment.

The capabilities of this study are underscored by the fact that it utilized an FDA-approved commercially available digital PCR assay. Such approval means that this technology is not only cutting-edge but also feasible for broad clinical application. By enabling precise assessments of minimal residual disease, digital PCR may greatly enhance patient management strategies and risk evaluations for those contemplating treatment-free remission.

With these advancements, Dr. Westerweel asserts that digital PCR for BCR::ABL1 is now a valuable and dependable tool that can aid clinicians in making informed treatment decisions for patients with chronic myeloid leukemia. As research continues to refine and expand the capabilities of molecular diagnostics, the promise of more personalized care for CML patients becomes increasingly attainable, offering hope for improved quality of life and the potential cessation of long-term therapies.

In conclusion, digitization in PCR methodology not only elevates the standard of precision in clinical evaluations but also represents a transformative leap toward understanding CML at a molecular level. This innovative approach signals a shift in how we view treatment options, with the potential to fundamentally alter the trajectory of care for individuals dealing with chronic myeloid leukemia.

Dr. Westerweel’s findings mark a significant stride in the realm of molecular diagnostics and personalized cancer therapy, demonstrating an exemplary fusion of technology and therapeutic strategy that may pave the way for future innovations in cancer treatment.

With the application of this digital technology, patients can anticipate more tailored treatment pathways and an era of precision medicine in which therapy aligns closely with individual patient needs. This achievement underscores the critical need for ongoing research and development in the ever-evolving landscape of oncology.

Subject of Research: Cells
Article Title: BCR::ABL1 Deep Molecular Response Quantification and Transcript Type Identification in Chronic Myeloid Leukemia Using a US Food and Drug Administration–Approved Droplet-Based Digital PCR Assay
News Publication Date: March 27, 2025
Web References: DOI Link
References: The Journal of Molecular Diagnostics
Image Credits: None provided.

Keywords: Chronic Myeloid Leukemia, Digital PCR, BCR::ABL1, TKI Discontinuation, Molecular Diagnostics, Precision Medicine, Transcript Type, Treatment-Free Remission.