Clinical scenario: Fever / drowsiness/ unsteady gait / weakness
An 8-year-old previously healthy boy is brought to the emergency department with fever followed by progressive drowsiness, unsteady gait, and right-sided weakness 10 days after recovery from a viral upper respiratory tract infection. On examination, he is disoriented, has truncal ataxia, brisk deep tendon reflexes, right extensor plantar response, and no neck stiffness. CSF examination shows 12 lymphocytes/mm³, mildly elevated protein, and normal glucose. Brain MRI reveals multiple bilateral, poorly defined hyperintense lesions involving the subcortical and deep white matter, basal ganglia, and thalami.
What is the most likely diagnosis?
A. Acute disseminated encephalomyelitis
B. Herpes simplex encephalitis
C. Multiple sclerosis
D. Neuromyelitis optica spectrum disorder
E. Tuberculous meningitis
Correct answer & Explanation:
Correct Answer: A. Acute disseminated encephalomyelitis
Explanation: Acute disseminated encephalomyelitis (ADEM)
This child has the classic presentation of acute disseminated encephalomyelitis (ADEM).
Key diagnostic features include:
- Recent viral infection (1–3 weeks earlier)
- Encephalopathy (confusion, altered consciousness), which is a hallmark of ADEM
- Multifocal neurological deficits (weakness, ataxia, pyramidal signs)
- Mild CSF lymphocytic pleocytosis with elevated protein
- MRI showing large, bilateral, poorly demarcated lesions involving both the white matter and deep gray matter (basal ganglia and thalami)
According to the IPMSSG, encephalopathy is required for the diagnosis of ADEM, helping distinguish it from a first episode of multiple sclerosis in children.
Why the other options are incorrect
A. Acute disseminated encephalomyelitis
Correct. The combination of post-infectious onset, encephalopathy, multifocal neurological deficits, and characteristic MRI findings is diagnostic.
B. Herpes simplex encephalitis
Usually presents with fever, altered consciousness, and seizures, but MRI predominantly involves the temporal lobes, and CSF often shows a more marked inflammatory response. HSV PCR is typically positive.
C. Multiple sclerosis
Children with MS usually do not present with encephalopathy. MRI lesions are typically well-circumscribed, periventricular, and disseminated in time and space.
D. Neuromyelitis optica spectrum disorder
Usually presents with optic neuritis and/or longitudinally extensive transverse myelitis. Brain MRI findings differ, and AQP4-IgG or MOG antibody testing may assist in diagnosis.
E. Viral cerebellitis
Causes acute ataxia but does not explain encephalopathy, pyramidal signs, or multifocal white matter lesions on MRI.
Learning Point
The most important distinguishing feature of ADEM in children is encephalopathy, together with multifocal neurological deficits and characteristic MRI findings. This helps differentiate ADEM from pediatric multiple sclerosis.
