Clinical Scenario:
An 8-year-old boy is brought to the emergency department with fever, headache, and altered sensorium for 2 days. Two weeks earlier, he had an upper respiratory tract infection that resolved spontaneously. On examination, he is confused and disoriented. He has bilateral extensor plantar responses and mild right-sided weakness. There are no meningeal signs. MRI brain shows multiple bilateral, poorly demarcated hyperintense lesions involving the subcortical and deep white matter. CSF reveals mild lymphocytic pleocytosis with normal glucose and mildly elevated protein.
What is the most likely diagnosis?
A. Acute disseminated encephalomyelitis
B. Herpes simplex encephalitis
C. Multiple sclerosis
D. Neuromyelitis optica spectrum disorder
E. Viral meningitis
Correct answer & Explanation:
Correct answer: A. Acute disseminated encephlomylitis
Discussion: Acute disseminated encephlomylitis (ADEM)
ADEM is an immune-mediated demyelinating disorder that typically occurs days to weeks after a viral infection or vaccination. It is characterized by:
Acute onset of encephalopathy (a required feature for pediatric ADEM diagnosis)
Multifocal neurological deficits
MRI showing large, bilateral, asymmetric, poorly defined white matter lesions
CSF with mild lymphocytic pleocytosis and elevated protein
The presence of encephalopathy together with multifocal MRI lesions following a recent infection strongly favors ADEM.
Why the Other Options Are Incorrect
B. Herpes simplex encephalitis
Usually affects the temporal lobes.
Seizures and focal deficits are common.
MRI typically shows temporal lobe involvement rather than diffuse multifocal white matter lesions.
C. Multiple sclerosis
Encephalopathy is uncommon at presentation.
Lesions are usually smaller, well-circumscribed, and periventricular.
First presentation in childhood is less common.
D. Neuromyelitis optica spectrum disorder
Typically presents with optic neuritis and/or longitudinally extensive transverse myelitis.
Diffuse encephalopathy is less characteristic.
E. Viral meningitis
Usually presents with headache, fever, and meningeal symptoms.
Multifocal neurological deficits and characteristic MRI white matter lesions are not expected.
Postgraduate Pearl
The single most important clinical clue favoring ADEM over multiple sclerosis in children is the presence of encephalopathy (altered consciousness or behavioral change) accompanying multifocal neurological deficits after a recent infection. MRI typically shows large, poorly marginated bilateral white matter lesions, whereas MS lesions are generally smaller, sharply defined, and periventricular.
