Clinical Reasoning: Acute and Progressive Cognitive Decline in a 38-Year-Old Man.

The differential diagnosis of multiple intracranial lesions is often perplexing and highly challenging, especially in the early stages. We present the case of a young man who initially presented with an acute headache and memory decline, which rapidly progressed to significant cognitive deterioration. Based on acute clinical manifestations, elevated CSF protein levels, and atypical MRI findings, the patient was initially misdiagnosed with idiopathic inflammatory demyelinating disease of the CNS. However, the rapid progression of symptoms and the enlargement of lesions on MRI raised further suspicion of cerebral venous sinus thrombosis, followed by primary angiitis of the CNS. Ultimately, digital subtraction angiography identified a rare intracranial vasculopathy, guiding appropriate management. The case highlights the importance of increased awareness in broadening the differential diagnosis, particularly in young patients presenting with acute cognitive decline and atypical imaging findings.