• Metabolic disease

A 78-year-old non-alcoholic man with acute alteration in consciousness and pendular nystagmus progressed to a comatose state. Recent medical history was significant for a 2-week period of severe vomiting and diarrhoea. Past medical history included diabetes mellitus and Helicobacter pylori duodenal peptic ulcer disease. Axial fluid-attenuated inversion recovery MRI evaluation showed abnormalities of the prepositus hypoglossal nuclei, medial vestibular nuclei, floccular lobes, cerebellar vermis, tectum of the midbrain, periaqueductal gray matter, mamillary bodies, thalami, anterior fornices and motor strips (figure 1). Findings were diagnostic for Wernicke encephalopathy (WE). The patient improved with thiamine therapy; however, due to the severity of disease, the patient developed Korsakoff's syndrome.

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Figure 1

(A) Note the alterations in the prepositus hypoglossal nuclei (arrows); (B) medial vestibular nuclei (arrowheads), floccular lobes (arrows); (C) vermis (asterisk), central gray matter (arrowhead); (D) tectum of the midbrain (arrows) mamillary bodies (arrowheads), vermis (asterisk); (E) fornix columns (arrowheads), periventricular region of the third ventricle (arrows); (F) motor strips (arrowheads).

Thiamine (vitamin B1) is needed by the cell membranes to sustain osmotic gradients and is also essential in glucose metabolism and neurotransmitter synthesis. WE, caused by a deficiency in thiamine, can present with ocular symptoms that include nystagmus, bilateral lateral rectus palsies and conjugate gaze defects from cranial nerve involvement of the oculomotor, abducens and vestibular nuclei. As demonstrated by MRI, selective brainstem cranial nerve nuclei involvement accounts for ocular abnormalities as well as for gait instability in WE-affected patients.1 Cortex, cerebellum and brainstem interact to activate the range of vertical ocular movements seen in normal subjects. It has been postulated that the disruption of feedback control of the eye velocity-to-position integrator, which maintains steady gaze by transforming velocity signal to eye position, is a mechanism of pendular nystagmus.2 The velocity-to-position neural integrator includes the prepositus hypoglossal nucleus, the interstitial nucleus of Cajal, the medial vestibular nucleus, the cerebellar flocculus and the paramedian tracts.3 In our patient, the signal intensity alterations from thiamine-related metabolic breakdown involving the prepositus hypoglossal nuclei, medial vestibular nuclei and floccular lobes may have damaged these neural integrators resulting in the development of pendular nystagmus. Thus, this selective thiamine-related metabolic breakdown, as correlated by MRI, may disrupt the normal ocular–motor feedback mechanism and account for the ocular motor defects seen in WE.