Question

A 10-year-old girl presents with fever and altered sensorium. MRI shows large, fluffy hyperintensities in the white matter and cerebellum on T2-weighted images. What is the most probable diagnosis?

• A. Autoimmune encephalitis
• B. Acute disseminated encephalomyelitis (ADEM)
• C. Multiple sclerosis (MS)
• D. Tuberculoma

Hint:

ADEM vs MS Key Clues:
$\bullet$ ADEM = Post-infectious + Encephalopathy mandatory + Large, fluffy, poorly marginated white matter/cerebellar lesions (Monophasic).
$\bullet$ MS = No encephalopathy + Dawson's fingers periventricular discrete lesions (Dissemination in time and space).

Answer 1

The Correct Option is B

Concept:
Acute Disseminated Encephalomyelitis (ADEM) is an acute, immune-mediated, post-infectious or post-vaccinal inflammatory demyelinating condition of the central nervous system.
It predominantly affects children and is characterized by acute multifocal neurological deficits combined with encephalopathy (altered mental status).
Explanation:
• Diagnostic criteria for ADEM require an acute or subacute onset of multifocal neurological symptoms accompanied by encephalopathy (lethargy, confusion, altered consciousness) not explained by fever alone.

• Brain MRI (T2-weighted and FLAIR sequences) characteristically reveals large ($>1\text{--}2\text{ cm}$), asymmetric, poorly marginated, "fluffy" or cloud-like hyperintense lesions involving the subcortical and deep cerebral white matter, basal ganglia, brainstem, and cerebellum.

• These lesions are typically in the same stage of evolution (monophasic demyelinating event).

• Multiple Sclerosis (MS): Lesions are typically small, well-demarcated, ovoid, located perpendicularly along the corpus callosum (Dawson's fingers), and clinical presentation rarely presents with prominent encephalopathy in pediatric onset.

• Autoimmune Encephalitis: Typically causes hyperintensities restricted to the limbic structures (medial temporal lobes) on MRI, presenting with severe behavioral changes, psychosis, and refractory seizures.

• First-line treatment for ADEM is high-dose intravenous pulse methylprednisolone ($30\text{ mg/kg/day}$ for $3$--$5$ days), leading to rapid clinical recovery.
Final Answer:
The clinical presentation of acute encephalopathy following a febrile episode with MRI demonstrating large, fluffy T2 hyperintensities in cerebral white matter and cerebellum is characteristic of Acute Disseminated Encephalomyelitis (ADEM).