Abstract
BACKGROUND: Acute disseminated encephalomyelitis (ADEM), which is rare, primarily affects children. It usually manifests as acute encephalopathy and multifocal neurological impairments after infection or vaccination. Diagnosis is still difficult due to the clinical and radiological similarity to other central nervous system disorders. Adult-onset ADEM calls for thorough reporting in order to improve diagnosis and treatment. CASE SUMMARY: A 55-year-old man with hypertension had a high fever, intense headache and a steady decline in his neurological function after two weeks. Left facial paralysis was the initial symptom, which progressed to left hemiparesis, reduced consciousness level, photophobia, phonophobia, vomiting, and a focal seizure in the right leg. He had no history of autoimmune disease, vaccinations, or infections. Investigations showed negative infectious/autoimmune serology, mild cerebrospinal fluid lymphocytic pleocytosis (protein 76 mg/dL), and lymphopenia. Brain magnetic resonance imaging without contrast revealed bilateral, symmetrical T2/fluid-attenuated inversion recovery hyperintensities, primarily in the middle cerebellar peduncles, with minor involvement in the pontine and periventricular regions. Neoplastic, metabolic, vascular, and infectious conditions were not included. The patient showed spontaneous neurological improvement by Week 3 with near-complete motor recovery (limb strength 4/5) after methylprednisolone and rehabilitation, despite logistical delays in starting immunotherapy. The monophasic course and radiological/clinical remission were supported by idiopathic ADEM. CONCLUSION: This case shows an uncommon, idiopathic, cerebellar-predominant ADEM variation in an adult without conventional triggers. It emphasizes the diagnostic difficulty in distinguishing ADEM from mimics (such as stroke or infection) in adults. Spontaneous improvement before treatment, although early detection is still crucial, should be highlighted, although early detection is still crucial. Increased clinician awareness, fair access to neuroimaging, and focused research on adult ADEM are crucial to fill these gaps and improve outcomes in places with limited resources.