Author(s): Glendaliz Bosques, MD, Susan Cabello-Porrata
Originally published: October 16, 2025 Last updated: October 16, 2025
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Disease/Disorder

Definition

Encephalopathy is a clinical syndrome— not a specific diagnosis —characterized by diffuse brain dysfunction resulting in altered mental status, often affecting cognition and/or level of arousal, and behavioral changes. It is typically multifactorial or related to a specific underlying cause, and is commonly associated with widespread, noninflammatory cerebral edema.1,2 “Toxin and metabolic encephalopathy” is therefore used when the underlying cause is exposure to neurotoxic substances.

Pediatric toxin and metabolic encephalopathy refers to a group of brain disorders in children caused by exposure to exogenous or endogenous substances that impair neuronal function. Clinical manifestations can vary depending on the offending agent, duration of exposure, and individual susceptibility.3

It is important to note that the terms “toxin and metabolic encephalopathy” (TME) and “toxic encephalopathy” are often used interchangeably in the medical literature, though there are some subtle differences. TME is a more specific term used to describe an encephalopathy caused by exogenous toxins, which have direct neurotoxic effects. In contrast, toxic encephalopathy is a broader term used to describe encephalopathy caused by endogenous or exogenous poisonous substances that lead to metabolic derangements.

Etiology

ME encompasses a broad spectrum of etiologies, often involving complex and multifactorial mechanisms. The causative agents can be broadly categorized into exogenous (externally derived) or endogenous (internally generated) toxins. Table 1 outlines examples from each category; however, it is not an exhaustive list.

A wide range of toxins can contribute to the development of encephalopathy. One well-characterized example is Shiga toxin-producing Escherichia coli (STEC), which induces both direct and indirect neuronal dysfunction.4 Another notable agent is salicylate, which disrupts mitochondrial function and leads to hyperammonemia, ultimately resulting in neural damage.5

Toxin and Metabolic Encephalopathy – Table 1

Epidemiology including risk factors and primary prevention

The epidemiology of TME is challenging to delineate due to the broad spectrum of causative agents. For instance, the incidence of STEC infection peaks in the summer and fall, with the highest rates occurring in children under five, an age group particularly susceptible to developing hemolytic uremic syndrome (HUS).4 Similarly, litchi fruit-associated encephalopathy tends to occur during the summer harvest season, primarily affecting children in parts of Southern Asia.6

Young age is a major risk factor, as infants and younger children are particularly vulnerable due to immature metabolic pathways and underdeveloped immune systems. Other important risk factors include underlying illness, incomplete or absent immunization, poor sanitation, malnutrition, low socioeconomic status, and environmental exposures.

Primary prevention strategies should be tailored to the specific causative agent and may include minimizing exposure to environmental toxins (e.g., removing lead-based paint), promoting proper hygiene, ensuring up-to-date vaccinations, and educating caregivers on safe medication storage to prevent accidental ingestion. Adherence to dosing guidelines is also essential to reduce the risk of neurotoxic side effects, alongside other targeted preventative measures.

Patho-anatomy/physiology

The mechanism by which toxins disrupt the nervous system involves a complex interplay of processes, including direct neurotoxicity, metabolic derangements, and excitotoxicity, all of which contribute to neuronal injury. These processes often result in widespread, symmetric brain damage affecting multiple structures, most commonly the cerebral cortex, white matter, thalamus, caudate nucleus, and pons.7 Some etiology-specific pathophysiologic patterns are summarized in Table 2.

Toxin and Metabolic Encephalopathy – Table 2

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

New onset/acute

The acute clinical presentation varies depending on the neurotoxic agent, with symptom onset typically occurring within hours to days following exposure. Initial symptoms typically include systemic manifestations specific to the toxin involved (e.g., gastroenteritis in STEC-HUS), with eventual presentation of neurological symptoms such as headache, lethargy, agitation, altered mental status, or seizures.1,2,15

Subacute

In the days to weeks following exposure, clinical symptoms may either gradually improve or progressively worsen, particularly if the toxic exposure persists. Some toxins, such as lead, exhibit a more insidious course, with symptoms relating to the blood concentration levels. Subtle findings during this phase may include irritability and behavioral changes.16–18 If progression continues, worsening confusion, developmental regression, neurocognitive decline, and coma are likely to develop.

Chronic/stable

Following the acute phase, symptoms may stabilize or partially improve over subsequent weeks to months. However, in cases of ongoing or repeated exposure, as seen with chronic lead toxicity, symptoms can include profound decline in energy levels, cognitive deficits, behavioral changes, sustained weakness, or motor impairments.15,16

Pre-terminal

In severe or untreated cases, progressive neurological deterioration can occur, in addition to multi-organ compromise. At this stage, persistent or deepening coma, loss of brainstem reflexes, autonomic instability, respiratory failure, and even death can ensue. The mortality rate in toxin-related encephalopathies among children varies greatly, with ranges reported between eight to over 75%.19

Specific secondary or associated conditions and complications

Prolonged exposure to the offending agent or delayed treatment initiation is often linked to long-term neurologic sequelae and multiorgan system complications. Specific secondary conditions might depend on the offending agent. Still, the commonly shared complications along the wide array of etiologies may include chronic seizures, intellectual disabilities, motor impairments, behavioral problems, and coma. The severity and duration of complications depend on the initial presentation, the child’s age, the initial immunological state, and the duration of exposure to the offending agent.

Toxin and Metabolic Encephalopathy – Table 3

Essentials of Assessment

History

Gathering a thorough history is essential when evaluating the child for suspected TME. Key elements include: exposure history, recent contact with ill individuals, travel history, current medications taken by the child or their caregivers, housing and environmental conditions, and a social history. Inquiring about recent illnesses, vaccination status of both the child and their caregivers, as well as past medical and family history, is also vital as they can indicate a possible inherited or predisposing condition.1,2

Documenting the timeline of symptoms is essential, as it can help distinguish new neurologic deficits from pre-existing ones. Establishing the child’s baseline functional status is crucial, as it aids in evaluating the severity and progression of the encephalopathy.  Acquiring a thorough developmental and functional history is instrumental in this patient population.

Physical examination

Conducting a comprehensive physical exam in an infant or a young patient with altered mental status can prove challenging. However, an initial assessment including vital signs, general physical appearance (e.g., skin turgor, signs of distress, whether the patient appears acutely ill) can usually be completed with relative ease. The presence of specific physical findings like skin rash, blue lines on the gums (suggesting lead poisoning), hand-flapping tremor (seen with uremia) can help guide the physician towards specific underlying etiologies.1,2,7

A focused neurological assessment is essential and should evaluate the patient’s level of consciousness, as well as neurological deficits (e.g., weakness, altered reflexes, changes in sensation, difficulty with balance or coordination). Focal deficit findings are usually uncommon, and their presence should prompt consideration for possible structural brain lesions.1,2 Additional system-specific examinations, including but not limited to cardiovascular, respiratory, and gastrointestinal, should be guided by the patient’s presenting symptoms.

Functional assessment

Initial assessments should include age-appropriate skills to determine the extent of functional impairment accurately. Depending on the presenting symptoms, consultations with physical, occupational, and speech therapy may be warranted. Evaluation should address mobility, transfers, ambulation, and locomotor skills. Additionally, assessments of activities of daily living (ADLs), fine motor skills, oromotor function, feeding and swallowing abilities, as well as cognitive, communication, and language skills, provide valuable insight into the child’s level of independence and functional capabilities, while also helping predict potential long-term outcomes. Functional assessment tools, such as WeeFIM (for children older than three years) and the Functional Status Scale (FSS),26 can be particularly useful. Neurocognitive evaluation, encompassing attention, memory, executive, and motor function, can be assessed through consultation with a neuropsychologist.

Laboratory studies

Laboratory studies are a key component in the diagnosis and monitoring of the patient’s condition. Routine blood tests, including a complete blood count and metabolic panel, help establish an initial clinical baseline and can aid in ruling out metabolic or infectious causes.1,2,15 Additional tests –such as serum ammonia, lactate, and ketone levels, as well as plasma acid–base status– can provide further insight, particularly for identifying subtypes of inherited metabolic conditions.27

Etiology-specific testing can be pursued. Testing for suspected causes

  • Environmental toxins: Check blood lead levels, peripheral blood smear, and carbon monoxide (CO) levels.
  • Infectious agent: Perform stool culture and polymerase chain reaction (PCR).
  • Accidental ingestion: Conduct a toxicology screening to identify potential causes.
  • Metabolic disorder: Check serum and urine amino acid levels, organic acids in urine, genetic testing.27

Imaging

Imaging serves as a valuable diagnostic tool when the clinical picture and laboratory workup are inconclusive. It may be critical in assessing the severity and extent of a neurological injury. While many offending agents present with diffuse brain edema, some toxins have distinct imaging patterns:28

  • Methotrexate: acute disseminated leukoencephalopathy. MRI findings typically reveal changes in the white matter of the cerebral hemispheres, corpus callosum, and brainstem.
  • Cyclosporine toxicity: posterior reversible encephalopathy syndrome pattern on MRI. It shows symmetric vasogenic edema on T2/FLAIR without diffusion restriction in white-matter of parieto-occipital regions.
  • Maple syrup urine disease: bilaterally symmetrical hyperintensities in dentate nuclei on T2/FLAIR imaging.
  • Toxin-induced hyperammonemia: symmetrical diffusion restriction involving insular and cingulate gyri on MRI.

Follow-up imaging during the later stages of the illness can be useful in visualizing disease progression and assessing the potential long-term damage.

Supplemental assessment tools

Electroencephalography (EEG) is a valuable tool when seizures are a prominent feature of the clinical presentation. It aids in distinguishing TME from other neurological conditions. The characteristic findings may include generalized, unilateral, or focal slowness, as well as low-voltage activity. Different patterns can consist of periodic lateralized epileptiform discharges and paroxysmal discharges.1,15

Lumbar puncture (LP) and cerebrospinal fluid (CSF) analysis can be used when there is a high index of suspicion for infection. This assists in identifying the toxin-producing microorganism in question or excludes infectious or inflammatory etiologies that can mimic TME.

Functional assessment tools, such as the WeeFIM (Functional Independence Measure for Children), a variant of the FIM scale, although limited, can provide insight into various domains of daily functional independence in children aged 6 months to 7 years.1 The Bayley Scales of Infant and Toddler Development (Bayley-3 and Bayley-4) are standardized scales that assess neurodevelopment from 1-42 months of age in domains including cognition, language, fine and gross motor, social-emotional and adaptive behaviors.

Neurobehavioral and cognitive assessment tools, such as WHO’s Neurobehavioral Core Test Battery or the Wechsler Intelligence Scale for Children (WISC), can be implemented and adapted to evaluate environmental or toxin-related cognitive effects in the pediatric population.9,15 The Cornell Assessment of Pediatric Delirium offers a validated bedside tool for screening for delirium in critically ill patients ranging from birth to 21 years old, while The Global Deterioration Scale (GDS) can prove helpful in categorizing levels of cognitive decline.29,30 Standardized measures of consciousness, such as the Coma Recovery Scale Revised (CRS-R) validated for children over 5 years old and the Coma Recovery Scale for Pediatrics (CRS-P) for toddlers, assess multiple domains, including visual, auditory, and communication responses for those with very severe cognitive impairments where arousal and awareness are being qeustioned.31

In the inpatient setting, tools such as the Physical Abilities and Mobility Scale (PAMS) can be used to track progress across a spectrum of motor abilities. In contrast, the Cognitive and Linguistic Scale (CALS), validated for age range from 2-21 years old, can be used to monitor age-appropriate progress of basic awareness to higher-level cognitive skills. The Montreal Cognitive Assessment (MoCA) is typically used for adults, but its validity in children has not been established.

Importantly, when implementing many of these tools, the presence of any preexisting developmental delays should be taken into consideration, as these can affect the interpretation of findings. When used in combination, these assessments help quantify the degree of impairment and guide management and rehabilitation strategies.

Early predictions of outcomes

Early prediction of outcomes remains challenging due to the heterogeneous nature of the etiologies and patient responses. Prognostic indicators include clinical, laboratory results, neurophysiological, and radiological factors. A low Glasgow Coma Scale (GCS) score is associated with a higher risk of poor outcomes. Additional negative prognostic markers include younger age, severe initial presentation, prolonged toxin exposure, immunocompromised status, pre-existing neurological disorder, and delays in medical intervention. Radiologic findings such as diffuse cerebral atrophy have been linked to unfavorable outcomes.1,2

Conversely, early medical interventions and prompt toxin removal are associated with better short- and long-term outcomes. Japanese studies have highlighted tools to assess long-term disability and prognosis. The Pediatric Cerebral Performance Category (PCPC) and The Pediatric Overall Performance Category (POPC) scales offer rapid bedside assessment in critical care settings, while the Wechsler Intelligence Test and the Tanaka–Binay test provide further prognostic insight.1

Environmental

Due to the multifactorial nature of TME, environmental needs and interventions can vary. Children with neurocognitive impairments may require modifications to the home environment to support safety and quality of life. For instance, children with mobility impairments might benefit from adaptations such as installing safety gates and removing tripping hazards.

In cases where encephalopathy is linked to environmental exposure, investigating, identifying and mitigating the source of exposure can aid in preventing recurrence in the affected child and also protect other members of the household. As physiatrists, we should advocate for stricter regulations on environmental toxins —specifically targeting industrial emissions and pesticide use— while also supporting investment in community education programs and remediation efforts.  

Social role and social support system

Long-term neurological sequelae following encephalopathy can significantly impact both the child’s and the family’s lifestyle. Understanding the child’s social role (e.g. student, sibling, peer) allows physicians to tailor long-term management and rehabilitation plans to support reintegration into daily life. Assessment of the family’s support system is equally important. Evaluating the availability and quality of emotional, financial and caregiving support helps ensure a more comprehensive and sustainable care. Recognizing and addressing these social factors, can help ensure proper emotional and physical support is provided.

Close collaboration between medical teams, school personnel, and families is essential. The evaluation of the child’s condition and the timing of re-integration into school should be individualized and guided by a multidisciplinary approach. Considerations include new academic services, accommodation, and gradual reintroduction to the classroom environment. Individualized educational plans (IEPs) should be developed based on the degree of impairment following a brain injury. A phased return to school with flexible attendance, rest breaks, and modified workload can help accommodate fatigue and attention difficulties. Children with more severe impairments may benefit from special education services or placement in supportive learning programs. Early and sustained rehabilitation programs can help improve functional outcomes, while ongoing counseling and social skills training are crucial for successful social reintegration.

Professional issues

Timely diagnosis and intervention are crucial to prevent irreversible damage, which can significantly impact the child’s quality of life. Ethical and safety concerns are notable given the vulnerability of the pediatric population and the limited availability of evidence-based diagnosis and management protocols for this population. Informed consent presents an ethical challenge, especially in cases where older patients are cognitively impaired and unable to make decisions. Environmental policies also play a crucial role in mitigating the effects associated with chemical and toxin exposure. Regulatory measures and standards to limit exposure should be enforced, along with supporting public health initiatives that aim to reduce environmental pollutants.

Rehabilitation Management and Treatments

Available or current treatment guidelines

Management of TME should be individualized and guided by the underlying etiology. Currently, there are no universal guidelines tailored explicitly for its treatment. Management generally follows principles from pediatric intensive care, toxicology, and rehabilitation medicine.

Initial intervention should focus on stabilizing the patient and addressing the underlying cause of the condition. Factors such as timely diagnosis, appropriate treatment of underlying health conditions, and identification of the causative organism play an important role in optimizing outcomes.

At different disease stages

New onset/acute

Acute management focuses on stabilizing the patient and addressing the underlying etiology. For any child presenting with a reduced level of consciousness, immediate assessment should follow the ABC approach (airway, breathing, and circulation).32 If cerebral edema is suspected, intracranial pressure monitoring is warranted—management options including mannitol or hypertonic saline. Consideration for transfer to the PICU should be made if there is airway compromise or hemodynamic instability. Prompt correction of metabolic disturbances, as well as seizure control with benzodiazepine or barbiturates, is critical.1 The potential curative interventions depend on the underlying offending agent. Table 4 lists some specific treatments in the acute setting.

Toxin and Metabolic Encephalopathy – Table 4

Early rehabilitation strategies should begin as soon as medically possible. Passive range of motion exercises and repositioning to prevent contracture in non-responsive patients are fundamental at this early stage.33

Subacute

In the subacute phase, ongoing treatment of the underlying etiology should continue if resolution has not yet occurred. Secondary infection surveillance and management are critical in patients with invasive devices.

An interdisciplinary rehabilitation team should initiate an age-appropriate, structured rehabilitation program that includes interventions such as early mobilization, postural control, cognitive stimulation, and neuropsychological screening. These interventions help optimize function and possibly set a foundation for long-term recovery.

Chronic/stable

Management in the chronic phase may depend on the severity and nature of the insult. Interventions can include long-term epileptic management, symptomatic relief for pain, spasticity, or behavioral dysregulation, and surveillance for neurodegenerative risks. As functional recovery progresses, patients may transition from inpatient rehabilitation to community-based rehabilitation services. During this period, close follow-up and support for caregiver training and social reintegration are vital.

Pre-terminal or end of life care

In cases of progressive deterioration or irreversible neurological damage, management should shift to comfort-focused care. Opioids can be considered for the management of pain and spasticity. Referral to pediatric palliative or hospice services may be warranted. Clear and compassionate communication about prognosis and care goals should be discussed with the family.

Coordination of care

Managing pediatric patients requires careful coordination with an interdisciplinary team. A collaborative approach ensures continuity of care and addresses the complex medical, functional, and psychosocial needs of the child. During hospitalization, clear information between teams (e.g., physicians, therapists, nurses, and rehabilitation specialists) is essential. Providing detailed information about the child’s medical status, medications, and progress helps ensure a smoother transition from the hospital to an outpatient setting.

In the recovery stage, involvement of a social worker or case manager can help plan post-discharge care by connecting families with the appropriate resources, including physical, occupational, and speech therapy, cognitive rehabilitation programs, and support groups. It is imperative to provide longitudinal care due to the heterogeneous nature of the disease and the potential for long-term sequelae to develop. A comprehensive coordination can improve outcomes.

Patient & family education

Providing education in an age-appropriate manner about the disorder and its management to both patients and their families is essential for setting realistic expectations and promoting adherence to treatment plans. Educational efforts should include information about the causative agent, the expected clinical course, available treatments, and preventive measures to avoid recurrence or complications. Involving caregivers in therapy sessions enables them to understand the child’s needs better and provides them with the tools to offer more effective support at home. Child life specialists may assist in communicating and educating children and their siblings about medical and prognostic information.

Measurement of treatment outcomes

Impairment-based outcomes can be tracked by using serial examinations and clinical scales, including the Global Deterioration Scale (GDS), Glasgow Coma Scale (GCS), Pediatric Cerebral Performance Category (PCPC). These tools assess neurological status and level of consciousness.1,19 Activity participation-based outcomes measure the child’s ability to engage in age-appropriate daily activities, communicate effectively, and regain functional mobility. Environmentally based outcomes focus on the effectiveness of caregivers in providing treatment, accessibility to rehabilitation services, as well as home and supportive modifications at home and in school. All together, they provide a comprehensive picture of the patient’s recovery journey.

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

Prompt recognition and standardized response protocols are essential for effective management. Early use of neuroimaging and assessment tools like GCS and PCPC can enhance diagnostic accuracy and increase the likelihood of favorable outcomes. Employing a multidisciplinary approach [i.e., neurologist, pediatric physiatrist, nurses, therapists] early in the treatment course can prove beneficial for long-term recovery. Educating caregivers on toxin exposure prevention and early warning signs are crucial for improving outcomes and reducing the risk of recurrence. Collaboration among specialists for prognostic discussions and functional implications is an essential role of the physiatrist in this patient population.

Cutting Edge/Emerging and Unique Concepts and Practice

The use of eculizumab for treating neurological symptoms associated with STE-HUS is a promising strategy that could lead to better outcomes and a faster recovery.34,35

The Global Deterioration Scale (GDS) can be useful for categorizing the severity of cognitive decline. Although the WeeFIM assesses functional independence in children aged 6 months to 7 years across various domains of daily living and in different settings, other assessment tools may also be used. Especially with patients who present with significant impairments, concerns may arise regarding content validity. Other measures, such as the Physical Abilities and Mobility Scale (PAMS)36 have provided high sensitivity, reliability and validity for patients with acquired encephalopathies and brain injuries in the acute and inpatient rehabilitation setting. The Cognitive and Linguistic Scale (CALS)37 may provide a more accurate, detailed and sensitive assessment of basic and higher-level cognitive and linguistic skills throughout recovery.

Gaps in the Evidence-Based Knowledge

Currently, there are no universally established protocols for managing pediatric TME. Research on both acute and long-term management of these conditions remains limited, with many treatment strategies extrapolated from adult practices or small anecdotal case series. A major challenge lies in the heterogeneous nature of the condition. Moreover, the exact pathophysiology of many toxins remains poorly understood, further complicating the development of evidence-based treatment guidelines. Standardized rehabilitation approaches are still needed.

While the best available evidence guides current clinical practice, ongoing research is necessary to develop more evidence-based protocols tailored to the pediatric population, with a particular emphasis on evaluating children with preexisting developmental delays. Additionally, the long-term neurological consequences in children remain poorly defined. The potential for delayed cognitive impairments and adult-onset neurodegenerative disorders remains an area of uncertainty. Longitudinal studies targeting this topic could guide early interventions that may mitigate future neurological sequelae.

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Author Disclosure

Glendaliz Bosques, MD
Nothing to Disclose

Susan Cabello-Porrata
Nothing to Disclose