Thiamine (vitamin B1) deficiency

Thiamine (vitamin B1) deficiency is a clinically heterogeneous nutritional disorder with central and peripheral neurological, cardiovascular, gastrointestinal, and metabolic manifestations, including Wernicke encephalopathy, Wernicke-Korsakoff syndrome, beriberi, and thiamine-deficiency-associated lactic acidosis.

It can present with psychiatric features such as behavioural and personality change, apathy, irritability, emotional lability, anxiety, and depressive symptoms, as well as cognitive impairment and reduced motivation. Less commonly, psychotic symptoms such as hallucinations and delusions have been reported as prominent or initial manifestations, including in the absence of overt delirium or the classical neurological features of Wernicke encephalopathy.

Other characteristic features include encephalopathy, ocular abnormalities such as nystagmus or ophthalmoplegia, and gait or truncal ataxia, as seen in Wernicke encephalopathy. The classical triad is present in only a minority of patients. Other neurological manifestations include peripheral sensorimotor neuropathy and paraesthesia. Respiratory symptoms such as tachypnoea and dyspnoea may occur, particularly in the setting of thiamine-deficiency-associated lactic acidosis or cardiovascular involvement. In more chronic deficiency, Korsakoff syndrome may develop, characterised by prominent anterograde and retrograde amnesia and confabulation.

From a multisystemic lens perspective, clinical features in other body systems include (but are not limited to):

• Cardiovascular: Tachycardia, peripheral oedema and heart failure, which may be high-output or, in severe cases, low-output (Shoshin) beriberi.

• Gastrointestinal: Anorexia, nausea, vomiting and abdominal discomfort.

• Musculoskeletal: Muscle weakness (which may accompany peripheral neuropathy) and, particularly in more prolonged deficiency, muscle wasting.

Early diagnosis is important because severe thiamine deficiency can represent a medical emergency, particularly when presenting with Wernicke encephalopathy or severe cardiovascular or metabolic complications. Prompt thiamine replacement can prevent potentially irreversible neurological injury, including progression to Korsakoff syndrome, as well as other serious complications. Because thiamine deficiency can present without the classical features of Wernicke encephalopathy, a high index of suspicion is important, particularly in people with risk factors such as alcohol use disorder, malnutrition, prolonged vomiting, malabsorption or recent gastrointestinal surgery.