Isolated Lateropulsion in Acute Lateral Medullary Infarction

A previously healthy 60-year-old man presented with a sudden inability to stand; whenever he tried, he would fall to his left. He noted no other symptoms, in particular, no vertigo, diplopia, dysarthria, paresthesia, numbness, weakness, or incoordination. On examination the sole abnormality found was that whenever he tried to stand, he would lean to the left and would fall unless supported (Figure 1). He was able to sit straight. Dilated fundus indirect ophthalmoscopy showed a disconjugate, counterclockwise (from the patient's point of view) offset of torsional eye position (Figure 2). Settings of the subjective visual horizontal were offset to the left by 21° in the left eye and by 28° in the right eye. Magnetic resonance imaging results on the day of the event were normal but 2 days later showed a small infarct in the left lateral medulla (Figure 3). The patient spent 4 days in the hospital and a month later could stand normally.

Irresistible falling to one side without hemiparesis is called lateropulsion. Ipsiversive lateropulsion occurs with lesions of the medulla that involve either the descending lateral vestibulospinal tract or the ascending dorsal spinocerebellar tract¹ ; it also occurs with lesions of the cerebellum that involve the ascending dorsal spinocerebellar tract. Contraversive lateropulsion occurs with lesions of the pons that involve the medial longitudinal fasciculus² or lesions of the midbrain that involve the red nucleus.³ With lateropulsion there are usually other brainstem or cerebellar symptoms and signs, such as vertigo, diplopia, and nystagmus; our patient was unusual because he had none of these symptoms. He did, however, also have a disconjugate offset of torsional eye position toward the side of the lateropulsion, without head tilt or skew deviation; in other words, he also had a partial ipsiversive ocular tilt reaction.⁴ An offset of torsional eye position inevitably produces an offset of the subjective visual horizontal (or vertical) in the same direction, but unless either torsional eye position is measured with a fundus camera or the subjective visual horizontal (or vertical) is measured with a rotating light bar, both these abnormalities—and therefore the significance of the patient's inability to stand—will be missed.⁴

Correspondence: Dr Halmagyi, Neurology Department, Royal Prince Alfred Hospital, Camperdown, NSW-2050, Sydney, Australia (Michael@icn.usyd.edu.au).

Author Contributions:Study concept and design: Thurtell and Halmagyi. Acquisition of data: Halmagyi. Analysis and interpretation of data: Akdal. Drafting of the manuscript: Akdal. Critical revision of the manuscript for important intellectual content: Akdal, Thurtell, and Halmagyi. Administrative, technical, and material support: Akdal, Thurtell, and Halmagyi.

Financial Disclosure: None reported.