Wernicke encephalopathy complicating hyperemesis gravidarum after delayed thiamine therapy for suspected thiamine allergy: a case report and review of 39 published cases

Abstract Background: Hyperemesis gravidarum (HG) is a common cause of thiamine deficiency during pregnancy and may progress to Wernicke encephalopathy (WE). Most treatment delays arise from missed diagnosis, but iatrogenic hesitation over suspected thiamine allergy has rarely been examined. Case presentation: We report a 35-year-old woman with HG at 15+4 weeks' gestation whose thiamine replacement was withheld for more than four weeks after a positive skin test at another hospital, despite no history of allergy. She later developed altered consciousness, blurred vision, and ataxia, with brain magnetic resonance imaging (MRI) showing symmetric hyperintensities in the thalami, frontal lobes, and dorsal brainstem. After multidisciplinary review concluded that the skin test was likely a false-positive irritant reaction, high-dose intravenous thiamine was administered without any allergic response; her mental status recovered within 24 hours. We also reviewed 39 published cases of WE secondary to HG identified in PubMed, Web of Science, CNKI, and Wanfang databases from January 2016 to June 2026 (40 cases including ours). The mean age was 26.9 years; vomiting began at a mean of 8.1 weeks and neurological symptoms at 15.9 weeks, after a mean of 7.1 weeks of vomiting. Only 55% had the complete classic triad; 85.3% of MRI scans were positive. Three mothers died (7.5%), all with delayed or inadequate thiamine replacement; 20% of patients had chronic neurological sequelae, including 17.5% with Korsakoff syndrome. Conclusions: A single positive thiamine skin test without a history of hypersensitivity must not delay parenteral thiamine in pregnant patients with persistent vomiting and neurological symptoms.