Dry beriberi, a neurologic manifestation of thiamine deficiency, presents as a symmetric, length-dependent polyneuropathy that may mimic acute neuromuscular syndromes such as Guillain-Barré and Miller Fisher syndromes. While rare in developed countries, thiamine deficiency may occur in patients with effective malnutrition from causes such as persistent vomiting. Glucagon-like peptide-1 (GLP-1) receptor agonists, including semaglutide, can cause significant gastrointestinal side effects leading to malnutrition and, in rare cases, micronutrient deficiencies.

This case illustrates a severe but reversible neurologic complication of semaglutide-induced malnutrition. Persistent gastrointestinal symptoms in patients receiving GLP-1 receptor agonists should prompt evaluation for nutritional deficiencies, including thiamine. Early empiric thiamine supplementation is critical, as prompt recognition and treatment can prevent irreversible neurologic injury. Clinicians should maintain a high index of suspicion and maintain a broad differential including malnutrition for patients with neuropathies on GLP-1 agonists, as rapid intervention can restore neurologic function and avert long-term disability.