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KembaraXtra-Medicine- Acute Disseminated Encephalomyelitis (ADEM)
Acute disseminated encephalomyelitis (ADEM) is an acquired inflammatory demyelinating syndrome of the central nervous system (CNS), most often occurring in children and frequently considered postinfectious in origin. It presents with acute-onset, widespread CNS inflammation and demyelination. Current diagnostic criteria emphasize the combination of acute polyfocal neurologic deficits with encephalopathy (a required core feature) and supportive brain MRI findings showing multifocal areas of increased T2/FLAIR signal.
ADEM is typically a monophasic illness, and more than 90% of children experience only a single event. Some children may develop evolving or new neurologic deficits within 90 days of symptom onset; this is still considered part of the same ADEM event rather than a relapse. When new attacks occur more than 90 days after onset, they may represent multiphasic ADEM (MDEM) or another demyelinating syndrome such as optic neuritis or transverse myelitis. A more fulminant variant, acute hemorrhagic leukoencephalitis (AHLE), can resemble ADEM clinically but progresses more rapidly and is associated with multifocal hemorrhages on imaging.
Epidemiologically, ADEM is most prevalent in school-aged children, with a mean age of onset around 5 to 8 years, and a slight male predominance. Incidence is estimated at 0.1 to 0.6 per 100,000 per year, with peak occurrence in winter and spring. Because ADEM is generally transient, prevalence estimates are not well established. Although ADEM can occur in adults, adult-onset cases tend to have a poorer prognosis than pediatric cases.
Clinically, many patients have a febrile illness in the weeks before neurologic symptoms, often an upper respiratory infection. Children may present with headache, vomiting, vision changes, gait disturbance, meningismus, and seizures (reported in about one-third of patients). The hallmark feature is encephalopathy, ranging from irritability and confusion to lethargy and coma. The spinal cord may be involved (transverse myelitis), producing motor and sensory deficits and possible bowel or bladder dysfunction, and cranial neuropathies—including optic neuritis—may occur. The course can be rapidly progressive, and severe cases may require intensive care monitoring.
The etiology is strongly linked temporally to recent infections, and molecular mimicry has been proposed as a mechanism, though definitive proof is lacking. ADEM has been reported following various infections, and case reports have described ADEM after COVID-19 infection; however, a causal role for SARS-CoV-2 has not been established. Importantly, recent comprehensive studies have not shown associations between ADEM and common vaccines, and while rare reports exist after SARS-CoV-2 mRNA vaccination, no causal relationship has been demonstrated.
Diagnosis is clinical and requires encephalopathy plus polyfocal deficits; MRI abnormalities alone are not sufficient in the absence of the key clinical features. The differential diagnosis includes neuromyelitis optica spectrum disorder (NMOSD) associated with aquaporin-4 antibodies, MOG-associated disease (MOGAD), multiple sclerosis (MS), meningitis/encephalitis, brain mass lesions, CNS vasculitis, AHLE, hemophagocytic lymphohistiocytosis, and certain metabolic or mitochondrial disorders. Although ADEM can rarely be the first event of MS, MS criteria require evidence of dissemination in time and space (often supported by CSF oligoclonal bands) and typically a non-ADEM clinical pattern.
Workup generally includes evaluation for infectious meningoencephalitis when clinically indicated, cerebrospinal fluid (CSF) analysis, and targeted serum testing. CSF often shows pleocytosis reflecting inflammation. Oligoclonal bands that are present in CSF but not serum are uncommon in ADEM and, while nonspecific, are more typically associated with MS. Serum testing for MOG-IgG is important because approximately half of children with ADEM have MOG antibodies at presentation, and most cases of multiphasic ADEM are MOG-antibody positive. MOG testing should be performed in serum (live cell-based assays with clearly positive titers are preferred), because CSF testing is less specific for MOGAD. Testing for AQP4-IgG is used to identify NMOSD, which is usually a chronic relapsing disease with potentially poor recovery without appropriate long-term management.
Neuroimaging is central to evaluation. Head CT is often performed initially to exclude mass lesions but can miss demyelinating disease due to low sensitivity for white matter changes. Brain and spine MRI with and without contrast is recommended and commonly shows disseminated T2/FLAIR hyperintense lesions across supratentorial and infratentorial white matter, cortex, deep gray matter, brainstem, optic nerves, and sometimes the spinal cord. Lesions are often bilateral, large, poorly demarcated, and only a minority enhance with gadolinium. Follow-up MRI after monophasic ADEM typically demonstrates improvement or resolution over subsequent months.
Treatment is focused on rapid anti-inflammatory therapy and supportive care. Many patients—especially those with severe encephalopathy, seizures, brainstem involvement, or respiratory compromise—require ICU monitoring. First-line therapy is high-dose intravenous corticosteroids, commonly methylprednisolone 30 mg/kg/day (maximum 1000 mg/day) for 3 to 5 days. If there is inadequate clinical improvement, second-line therapies include intravenous immunoglobulin (IVIG) totaling 2 g/kg divided over 2 to 5 days, or 5 to 7 plasma exchanges.
Most patients improve with short-course corticosteroids and do not require a prolonged steroid taper. Long-term steroids are not indicated, even when MOG antibodies are present. Chronic immunomodulatory therapy is reserved for patients who are diagnosed with relapsing conditions such as NMOSD, relapsing MOGAD, or MS, and should be guided by neuroimmunology specialists. A single MOG-related demyelinating event generally does not require chronic immunotherapy, and currently there are no reliable biomarkers that predict which MOGAD patients will relapse.
Disposition depends on severity; significant encephalopathy, seizures, increased intracranial pressure concerns, or ventilatory dysfunction warrant inpatient—and often ICU—care until stabilization. Neurology consultation is recommended for diagnosis, treatment planning, and follow-up. Clinically, the appearance of relapses or new lesions beyond the expected monophasic window is not consistent with monophasic ADEM and should prompt reassessment for multiphasic ADEM, MOGAD, NMOSD, or MS.
Acute disseminated encephalomyelitis (ADEM) is an acquired inflammatory demyelinating syndrome of the central nervous system (CNS), most often occurring in children and frequently considered postinfectious in origin. It presents with acute-onset, widespread CNS inflammation and demyelination. Current diagnostic criteria emphasize the combination of acute polyfocal neurologic deficits with encephalopathy (a required core feature) and supportive brain MRI findings showing multifocal areas of increased T2/FLAIR signal.
ADEM is typically a monophasic illness, and more than 90% of children experience only a single event. Some children may develop evolving or new neurologic deficits within 90 days of symptom onset; this is still considered part of the same ADEM event rather than a relapse. When new attacks occur more than 90 days after onset, they may represent multiphasic ADEM (MDEM) or another demyelinating syndrome such as optic neuritis or transverse myelitis. A more fulminant variant, acute hemorrhagic leukoencephalitis (AHLE), can resemble ADEM clinically but progresses more rapidly and is associated with multifocal hemorrhages on imaging.
Epidemiologically, ADEM is most prevalent in school-aged children, with a mean age of onset around 5 to 8 years, and a slight male predominance. Incidence is estimated at 0.1 to 0.6 per 100,000 per year, with peak occurrence in winter and spring. Because ADEM is generally transient, prevalence estimates are not well established. Although ADEM can occur in adults, adult-onset cases tend to have a poorer prognosis than pediatric cases.
Clinically, many patients have a febrile illness in the weeks before neurologic symptoms, often an upper respiratory infection. Children may present with headache, vomiting, vision changes, gait disturbance, meningismus, and seizures (reported in about one-third of patients). The hallmark feature is encephalopathy, ranging from irritability and confusion to lethargy and coma. The spinal cord may be involved (transverse myelitis), producing motor and sensory deficits and possible bowel or bladder dysfunction, and cranial neuropathies—including optic neuritis—may occur. The course can be rapidly progressive, and severe cases may require intensive care monitoring.
The etiology is strongly linked temporally to recent infections, and molecular mimicry has been proposed as a mechanism, though definitive proof is lacking. ADEM has been reported following various infections, and case reports have described ADEM after COVID-19 infection; however, a causal role for SARS-CoV-2 has not been established. Importantly, recent comprehensive studies have not shown associations between ADEM and common vaccines, and while rare reports exist after SARS-CoV-2 mRNA vaccination, no causal relationship has been demonstrated.
Diagnosis is clinical and requires encephalopathy plus polyfocal deficits; MRI abnormalities alone are not sufficient in the absence of the key clinical features. The differential diagnosis includes neuromyelitis optica spectrum disorder (NMOSD) associated with aquaporin-4 antibodies, MOG-associated disease (MOGAD), multiple sclerosis (MS), meningitis/encephalitis, brain mass lesions, CNS vasculitis, AHLE, hemophagocytic lymphohistiocytosis, and certain metabolic or mitochondrial disorders. Although ADEM can rarely be the first event of MS, MS criteria require evidence of dissemination in time and space (often supported by CSF oligoclonal bands) and typically a non-ADEM clinical pattern.
Workup generally includes evaluation for infectious meningoencephalitis when clinically indicated, cerebrospinal fluid (CSF) analysis, and targeted serum testing. CSF often shows pleocytosis reflecting inflammation. Oligoclonal bands that are present in CSF but not serum are uncommon in ADEM and, while nonspecific, are more typically associated with MS. Serum testing for MOG-IgG is important because approximately half of children with ADEM have MOG antibodies at presentation, and most cases of multiphasic ADEM are MOG-antibody positive. MOG testing should be performed in serum (live cell-based assays with clearly positive titers are preferred), because CSF testing is less specific for MOGAD. Testing for AQP4-IgG is used to identify NMOSD, which is usually a chronic relapsing disease with potentially poor recovery without appropriate long-term management.
Neuroimaging is central to evaluation. Head CT is often performed initially to exclude mass lesions but can miss demyelinating disease due to low sensitivity for white matter changes. Brain and spine MRI with and without contrast is recommended and commonly shows disseminated T2/FLAIR hyperintense lesions across supratentorial and infratentorial white matter, cortex, deep gray matter, brainstem, optic nerves, and sometimes the spinal cord. Lesions are often bilateral, large, poorly demarcated, and only a minority enhance with gadolinium. Follow-up MRI after monophasic ADEM typically demonstrates improvement or resolution over subsequent months.
Treatment is focused on rapid anti-inflammatory therapy and supportive care. Many patients—especially those with severe encephalopathy, seizures, brainstem involvement, or respiratory compromise—require ICU monitoring. First-line therapy is high-dose intravenous corticosteroids, commonly methylprednisolone 30 mg/kg/day (maximum 1000 mg/day) for 3 to 5 days. If there is inadequate clinical improvement, second-line therapies include intravenous immunoglobulin (IVIG) totaling 2 g/kg divided over 2 to 5 days, or 5 to 7 plasma exchanges.
Most patients improve with short-course corticosteroids and do not require a prolonged steroid taper. Long-term steroids are not indicated, even when MOG antibodies are present. Chronic immunomodulatory therapy is reserved for patients who are diagnosed with relapsing conditions such as NMOSD, relapsing MOGAD, or MS, and should be guided by neuroimmunology specialists. A single MOG-related demyelinating event generally does not require chronic immunotherapy, and currently there are no reliable biomarkers that predict which MOGAD patients will relapse.
Disposition depends on severity; significant encephalopathy, seizures, increased intracranial pressure concerns, or ventilatory dysfunction warrant inpatient—and often ICU—care until stabilization. Neurology consultation is recommended for diagnosis, treatment planning, and follow-up. Clinically, the appearance of relapses or new lesions beyond the expected monophasic window is not consistent with monophasic ADEM and should prompt reassessment for multiphasic ADEM, MOGAD, NMOSD, or MS.
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