Diagnostic criteria and course
Establishing the diagnosis of ADEM (ADEM) is based on the exclusion of other pathologies and compliance with the 2012 IPMSSG consensus criteria. To confirm the disease, a patient must present with all of the following features simultaneously:
- First-ever episode of polyfocal neurological deficit combined with encephalopathy.
- Encephalopathy (alteration in consciousness or behavior) cannot be explained by systemic infection, fever, or a postictal state.
- An inflammatory process leading to acute demyelination is presumed.
- Characteristic brain MRI changes identified within the first three months of the disease.
- Complete absence of new clinical symptoms and fresh MRI lesions 3 months or more after disease onset.
Classic ADEM has a monophasic course. This means that the active phase resolves within 3 months, followed by radiological and clinical improvement. Monophasia can only be definitively confirmed retrospectively by performing a follow-up MRI at 3 months.
If new lesions or symptoms appear after this period, there is a high probability that multiple sclerosis (MS) or neuromyelitis optica spectrum disorder (NMOSD) is masked under the guise of ADEM. True multiphasic form (a new isolated episode after 3 months without further relapses) is extremely rare — in less than 4% of cases.
MRI semiotics in ADEM
Neuroimaging plays a key role, although in rare cases the MRI picture may remain normal in the first days or even throughout the entire course of the disease.
Brain: T2-weighted and FLAIR images show multiple diffuse hyperintense areas. The lesions are usually large (greater than 1–2 cm in size), confluent, and poorly demarcated (poorly demarcated). They are predominantly located in the subcortical white matter of the cerebral hemispheres as well as at the grey-white matter junction. In children, the deep grey matter (thalami and basal ganglia) is frequently involved. Important: ADEM should not feature T1-hypointense lesions, and contrast enhancement is usually absent or mild.
Spinal cord: Involved in approximately one-third of patients, most often in the cervical and upper thoracic regions. Longitudinally extensive transverse myelitis (LETM) is characteristic: poorly demarcated T2-hyperintense lesions span multiple vertebral segments at once. Axial slices show that the pathological process can occupy more than 2/3 of the cross-section of the spinal cord. The lesions are expansive, causing local edema, and appear hypointense on T1-weighted images.
Differential diagnosis with multiple sclerosis
For treatment selection, it is critically important to distinguish monophasic ADEM from the manifestation of multiple sclerosis at the imaging stage.
| Sign | ADEM (ADEM) | Multiple sclerosis (MS) |
|---|---|---|
| Lesion size and contours | Large (>1–2 cm), confluent, poorly defined | Smaller, with clear, sharp borders |
| Brain localization | Predominantly subcortical white matter | Deep and periventricular white matter |
| Contrast enhancement | Typically do not enhance | Often demonstrate pronounced enhancement |
| MRI dynamics (at 6 months) | Complete or significant resolution of lesions | Persistence of old lesions, incomplete resolution |
| New lesions (>3 months) | Do not appear (in monophasic course) | Appearance of new lesions is typical |
Atypical and severe variants of the disease
In clinical practice, several specific syndromes are distinguished that are considered ADEM subtypes or closely related conditions.
Bickerstaff brainstem encephalitis (Bickerstaff encephalitis) This is a rare variant of localized brainstem encephalitis. It manifests with ataxia, ophthalmoparesis, and variable reflexes occurring after a fever. T2-weighted imaging visualizes a massive hyperintense lesion in the midbrain and pons. The disease has a favorable prognosis: the clinical presentation and MRI changes resolve completely. Oligoclonal bands are absent in the CSF, making classical demyelination unlikely.
Acute hemorrhagic leukoencephalitis (Hurst disease / Hurst disease) The hyperacute and most severe form of ADEM, often occurring after influenza. It is characterized by the rapid progression of symptoms: fever, hemiplegia, aphasia, seizures, and rapid deterioration of consciousness into coma. Autopsy reveals marked cerebral edema with multiple petechial hemorrhages around necrotic venules. Unlike ordinary ADEM, Hurst disease features a predominance of neutrophils in demyelinating lesions and CSF, and the outcome is most often fatal.
Briefly: answers to topical questions
What specific neuropsychiatric and neurological symptoms are part of the clinical picture of Bickerstaff brainstem encephalitis?
The clinical picture of Bickerstaff brainstem encephalitis (Bickerstaff encephalitis) includes the following specific neurological symptoms, which are usually preceded by a febrile illness:
- Ataxia is one of the main clinical signs.
- Ophthalmoparesis is a characteristic manifestation of the disease.
- Reflex abnormality — reflexes are variable, which distinguishes this pathology from Miller Fisher syndrome, in which they are significantly diminished or completely absent.
What are the differential diagnostic differences between acute disseminated encephalomyelitis and neuromyelitis optica spectrum disorders (NMOSD)?
The differential diagnosis between acute disseminated encephalomyelitis and neuromyelitis optica spectrum disorders (NMOSD) includes the following differences:
| Sign | Acute disseminated encephalomyelitis | NMOSD |
|---|---|---|
| Biomarkers | No specific biomarkers | Key marker: aquaporin-4 antibodies (AQP4-IgG) |
| Clinic | Polyfocal neurological symptoms and encephalopathy | Predominant involvement of the optic nerves and spinal cord |
| Course | Usually monophasic | — |
| Associated conditions | — | Often associated with other autoimmune diseases |
| Epidemiology | More commonly affects children; no sex predilection | Very low incidence |
ADEM = Acute, Diffuse, Encephalopathic, Monophasic. These four words reflect the main criteria: acute onset with encephalopathy, diffuse large MRI lesions, and a monophasic course without relapses.
Class and exam questions
Does a normal MRI in the first days rule out the diagnosis of ADEM?
No. The appearance of MRI lesions may be delayed by more than a month from the onset of clinical manifestations, and in some cases, neuroimaging remains normal throughout the entire disease period.
What is the difference between Bickerstaff brainstem encephalitis and Miller Fisher syndrome?
Miller Fisher syndrome is a pathology of the peripheral nervous system (with marked reduction or absence of reflexes), whereas Bickerstaff encephalitis affects the CNS (brainstem), and reflexes remain variable in this condition.
What is multiphasic ADEM?
This is an extremely rare form of the disease (less than 4%) in which a new episode of encephalopathy with demyelinating lesions occurs at least 3 months after the first attack, with no further relapses following it.
What is the prognosis for Hurst's disease?
The prognosis is extremely poor. Hurst's disease is a hyperacute hemorrhagic variant of encephalomyelitis with total brain edema, hemorrhages, and necrosis, which typically leads to a fatal outcome.
What else to study on this topic
- Detailed MRI semiotics of longitudinally extensive transverse myelitis (LETM) in various autoimmune pathologies.
- CSF changes in demyelinating diseases: lymphocytic pleocytosis versus neutrophilic.
- Diagnostic criteria for neuromyelitis optica spectrum disorders (NMOSD) and the role of specific antibodies (NMO IgG).
- Myelopathy in systemic lupus erythematosus: pathogenesis, clinical presentation, and prognosis.
- Anti-GQ1b IgG antibody syndrome and its clinical manifestations.
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