The disease is marked by inflammatory or degenerative changes of the nerves, digestive system, and heart and caused by a lack of or inability to assimilate thiamine. Early symptoms of beriberi are nonspecific and include fatigue, irritability, restlessness, loss of appetite, and vague abdominal discomfort. As the disease progresses, patients develop burning sensations, tingling in the extremities, and changes in sensation such as numbness. Patients may develop psychosis.
Death is generally a result of heart failure.