Wernicke's encephalopathy is a common disorder in patients with poor nutrition resulting in a thiamine deficiency. The hemorrhagic lesions characteristic of this disorder are found in the hypothalamus, mamillary bodies, and periventricular and periaqueductal regions of the brainstem (Fig. 15.9). The cardinal symptoms and signs are ophthalmoplegia, confusion, and gait ataxia. The ophthalmoplegia initially begins as gaze-evoked nystagmus and then progresses to gaze palsies. The nystagmus is most often horizontal, less commonly vertical, and rarely rotary. If not treated with parenteral thiamine, the patient develops total ophthalmoplegia, coma, and eventual death. The mortality rate is 10 to 20%.
Figure 15.9. Wernicke's encephalopathy. Autopsy sections from a 29-year-old patient with nasopharyngeal carcinoma who received intravenous fluids without thiamine replacement. Hemorrhagic lesions in the mammillaiy bodies (A) and in the periventricular regions of the brainstem (B) are characteristic of Wernicke's encephalopathy. (From Schochet SS Jr, Nelson J. Atlas of Clinical Neuropathology. Norwalk, CT: Appleton & Lange, 1989. Used with permission of the publisher.)
Those most at risk for Wernicke's encephalopathy are alcoholics, chronically ill patients with poor nutrition, and patients with anorexia or bulimia. The physician can precipitate Wernicke's encephalopathy by giving intravenous fluids containing glucose but not thiamine. The ocular motility findings begin improving quickly with the administration of intravenous thiamine.
Functional Gaze Palsies
Although functional gaze palsies are rare, the physician needs to know how to differentiate them from organic lesions. If a horizontal-gaze palsy is seen, the physician should look closely for evidence of miosis during attempted gaze. This finding would suggest the use of the near reflex to suppress gaze. To evaluate the integrity of the infranuclear structures, nuclei, nerves, and muscles, the VOR should be stimulated with either oculocephalic maneuvers, calorics, or chair rotation. OKN testing can be done with the initial targets being gradually moved into the paretic field of gaze on repeated testing. Testing of refixation saccades by gradually moving the targets into the paretic field of gaze can be informative also. Pursuit can be evaluated by putting a large mirror in front of the patient. The mirror is then turned either to the right or left for horizontal-gaze palsies or up and down for vertical-gaze palsies. The physician watches for movement of the eyes as they follow the moving facial image. Documentation of intact movements of the eyes with these maneuvers proves the functional character of the complaint.