2026 American Academy of Neurology Abstract Website

Objective:

Background:

Acute disseminated encephalomyelitis (ADEM) is an inflammatory central nervous system disorder characterized by acute encephalopathy and demyelinating lesions in the brain and/or spinal cord, more commonly seen in children than adults. Classic radiographic findings include diffuse, poorly demarcated, bilateral T2 hyperintense lesions with punctate or arc enhancement. Less commonly, ADEM presents as a unilateral lesion with significant vasogenic edema, which can mimic neoplasm. As no specific biomarker has been identified, ADEM remains a clinical diagnosis supported by history and neuroimaging, and a broad differential diagnosis should be considered in atypical cases. We present a rare case of adult-onset ADEM presenting as a unilateral, mass-like lesion with malignant cerebral edema, initially suggestive of tumor.

Design/Methods:

Results:

A 37-year-old woman with schizoaffective disorder was found unresponsive and presented with a first-time generalized tonic-clonic seizure. Head CT showed a 3.1 cm left frontal lesion with surrounding edema, midline shift, and early herniation. Despite medical management with high-dose corticosteroids and antiepileptics, she developed obtundation and signs of increased intracranial pressure, necessitating intubation and escalation to neurocritical care. Emergent hyperosmolar therapy was administered for malignant cerebral edema. MRI demonstrated extensive T2/FLAIR hyperintensity in the left frontal lobe, patchy enhancement, and diffusion restriction involving the left corona radiata and splenium of the corpus callosum, raising concern for primary intracranial neoplasm. Worsening edema and midline shift prompted emergent decompressive hemicraniectomy with biopsy. Pathology revealed a demyelinating process without malignancy.

Conclusions:

This case highlights the diagnostic and therapeutic challenges of fulminant ADEM mimicking intracranial neoplasm. Historically considered monophasic, ongoing debate regarding multiphasic ADEM complicates differentiation. The distinct clinical features in adults demonstrate a need for adult-specific diagnostic criteria. In rapidly deteriorating patients with significant mass effect, early surgical intervention may be necessary for definitive diagnosis. Recognition of atypical ADEM presentations is essential to avoid misdiagnosis and ensure appropriate management.