INTRODUCTION: Wernicke's encephalopathy is an acute neuropsychiatric syndrome 
resulting from a thiamine deficit, which is defined by the characteristic triad 
of confusion, ophthalmoparesis and ataxia, although rare presentations have been 
reported that delay its diagnosis. Miller Fisher syndrome is characterised by 
the triad ophthalmoparesis, ataxia and areflexia and is considered to be a 
variant of Guillain-Barré syndrome; its differential diagnosis includes 
Wernicke's encephalopathy.
CASE REPORT: A 75-year-old female with chronic digestive disorders, who 
developed an acute picture of bilateral internuclear ophthalmoplegia, ataxia and 
areflexia, with proteinocytologic dissociation in cerebrospinal fluid; 
accordingly, an initial diagnosis of Miller Fisher syndrome was proposed. 
Results of the neurophysiological studies were normal; anti-GQ1b antibodies were 
negative; and magnetic resonance imaging of the brain suggested Wernicke's 
encephalopathy. The response to thiamine was spectacular.
CONCLUSIONS: The similarities in the distribution of the lesions of the two 
conditions, in the signs and symptoms and the lab findings, as well as the 
influence of certain misleading factors (hyponatremia, advanced age), went to 
make up a typical syndrome that favoured a wrong presumptive aetiological 
diagnosis. This was corrected at an early stage, however, in light of the 
results of certain diagnostic tests and after observing the therapeutic 
response. In addition to being an atypical presentation for Wernicke's 
encephalopathy, this case highlights the fact that for there to be an agreement 
between the syndromic and aetiological diagnoses it is necessary to carry out a 
correct differential diagnosis based on details from the patient's history, on 
appropriate complementary tests and on the follow-up study of how the patients 
progress, even when we come across typical syndromes that are usually related to 
a predominant aetiopathogenesis.