Preventable cerebral venous sinus thrombosis from diet- and alcohol-induced hyperhomocysteinemia: illustrative case.

backgroundCerebral venous sinus thrombosis (CVST) is a rare stroke subtype (0.5%-3%) that frequently presents with nonspecific symptoms, delaying diagnosis. Although hyperhomocysteinemia is a known risk factor, acquired cases resulting from severe vitamin B12 and folate deficiencies can be easily overlooked by clinicians in any setting, making this a critical yet preventable cause of life-threatening thrombosis. OBSERVATIONS: A 44-year-old man with obesity, who adopted a carbohydrate-heavy diet and consumed excessive alcohol (70-140 g/day) following a major life event 3 years prior, presented with worsening headache, somnolence, and right-sided neurological deficits. Imaging confirmed CVST with bilateral parietal venous infarction and left-sided hemorrhage. Severe hyperhomocysteinemia (143.4 nmol/mL) secondary to critically low vitamin B12 and folate levels was identified, likely induced by these lifestyle changes. Anticoagulation therapy, vitamin supplementation, alcohol cessation, and nutritional counseling improved clinical symptoms, with normalization of homocysteine levels within 30 days, despite persistent evidence of brain tissue damage on imaging. LESSONS: This case highlights the serious consequences of severe vitamin deficiencies, triggered by lifestyle changes, in causing significant CVST, regardless of location. It emphasizes the importance of prioritizing detailed history-taking to identify modifiable lifestyle factors, facilitating timely intervention to manage symptoms, normalize homocysteine levels, and prevent recurrence. https://thejns.org/doi/10.3171/CASE25759.