What are the clinical features of Acute Disseminated Encephalomyelitis (ADEM)?

Clinical Features of Acute Disseminated Encephalomyelitis (ADEM)

Acute Disseminated Encephalomyelitis (ADEM) presents with encephalopathy accompanied by multifocal neurologic deficits affecting various parts of the central nervous system, often following an infectious illness or vaccination. 1

Core Clinical Presentation

• Encephalopathy is a required component for ADEM diagnosis, ranging from confusion to coma, and is often the predominant feature 1
• Behavioral changes (41%) are among the most common features, along with disorientation (76%) and speech disturbances (59%) 2
• Seizures occur in approximately one-third of patients with ADEM 2
• Fever is common, with up to 80% of patients presenting with febrile illness 2
• Focal neurological deficits are present in 36-78% of cases 2

Neurological Manifestations

• Optic neuritis, which may be bilateral, is a common neurological manifestation 1
• Myelitis, often longitudinally extensive, frequently occurs in ADEM patients 1
• Ataxia is a common presenting feature, seen in more than half of pediatric cases 3
• Brainstem encephalitis and cerebellar ataxia can occur 1
• Motor deficits, including weakness, are present in many cases 3
• Headache is a frequent symptom, particularly in children 3

Age-Specific Considerations

• In children, the presentation may be more polysymptomatic with encephalopathy, fever, and meningeal signs 4
• In adults, encephalopathy is less frequent, and the clinical picture is usually dominated by long tract involvement 4
• Children may present with non-specific symptoms including feeding and respiratory difficulties 2
• Confusion, irritability, or behavior changes are seen in up to 76% of pediatric cases 2

Diagnostic Clues

• Recent history of infection (31%) or vaccination (4%) may be present 5
• A normal Glasgow Coma Score at presentation can be seen in some patients, as it may not detect subtle behavioral changes 2
• ADEM should be suspected in patients with acute onset of multifocal neurological deficits, especially following a febrile illness or vaccination 1, 2
• Subtle presentations may include low-grade pyrexia rather than high fever, speech disturbances, and behavioral changes that can be mistaken for psychiatric illness 2

Distinguishing ADEM from Other Conditions

• ADEM is more common in children than adults and typically has a monophasic course, distinguishing it from multiple sclerosis 6
• Seizures are more common in patients with encephalitic processes affecting the cortex (often infectious) compared to those predominantly affecting subcortical white matter (like ADEM) 2
• However, ADEM can sometimes be relapsing, which poses a diagnostic challenge for distinguishing it from multiple sclerosis 6
• Approximately 9.5% of patients initially diagnosed with ADEM may subsequently be diagnosed with multiple sclerosis 7

Clinical Course and Prognosis

• Although the outcome is generally favorable in most cases, some patients may experience relapse after cessation of steroids 1, 3
• Approximately 28% of children may have ongoing disabilities despite treatment 3
• Symptoms may flare up after tapering of oral steroids, suggesting steroid-dependence in some cases 1
• Despite initial clinical severity, functional outcome is favorable in most cases 4

Pitfalls and Caveats

• Brain CT scans are often normal in ADEM (78% of cases), which can be falsely reassuring and delay diagnosis 3, 5
• MRI is the imaging modality of choice for diagnosis, revealing characteristic findings such as large, confluent T2 brain lesions 1
• Delays in diagnosis can result in considerable morbidity, highlighting the importance of early recognition and treatment 3
• The differential diagnosis is broad and includes infectious, metabolic, vascular, neoplastic, and toxic etiologies 2