In 1976, Selenick et al., observed a patient in whom the eyes deviated slowly and conjugately from one lateral side to the opposite side with a fixed frequency, without pausing at the most lateral positions. This disorder of eye movement was designated as the ping-pong gaze (PPG).
A 75-year-old male patient with a history of hypertension, coronary artery disease, and coronary bypass was found to be unconscious in bed and taken to the emergency department. The patient was comatose and nonresponsive to speech and painful stimuli. He had a Glasgow Coma Score of 5. The body temperature was 36.6°C, pulse 109 beats/min, and blood pressure 168/87 mmHg. During the neurologic examination, a noxious stimuli or holding the eyelids open did not alter the movements of the eye. The eyes moved conjugately and smoothly from one extreme of gaze to the other, returning without pause or nystagmus. Each cycle lasted for 3–5 s [Video 1]. The pupils had a diameter of 3 mm bilaterally and were slowly and consensually reacting to light and painful stimuli. The other cranial nerves were unremarkable. The muscle tone was increased throughout with rigidity of the left extremities. The deep tendon reflexes were 3+ and the Babinski's sign was present on the left side. He was evalaued with a brain magnetic resonance imaging that showed lesions consistent with an hyperintense acute infarct on diffusion-weighted sequences in the right middle cerebral artery area. [Figure 1]. His hematologic, biochemical and serological examinations were normal.
Figure 1: Hyperintense acute infarct on diffusion-weighted sequences in the right middle cerebral artery area
Our patient demonstrated the short-cycle periodic alternating gaze or periodic alternating PPG. Periodic alternating PPG is a continuous eye movement characterized by conjugate movements laterally from side to side at a rate of 3 to 7 s/cycle. It is usually smooth, but a saccadic form has been described., Fisher described this clinical feature in a patient with bilateral hemispheric infarction. PPG has also been observed in patients with vermian hemorrhage, that involved bilateral crura cerebri, and mesencephalic tegmentum, and in intoxicated patients.,, The mechanism of PPG is not yet fully understood, but it is usually seen in patients with bilateral impairment of the cerebral hemispheres or bilateral disconnection of the cerebrum from the brain stem.,,,,
To the best of our knowledge, PPG secondary to unilateral hemispheric ischemic stroke has not been reported. Further studies are needed to clarify the mechanism behind PPG. When encountering stroke survivors with PPG, we should keep in mind that this unique syndrome is related not only to bilateral hemispheric infarction but also to an unilateral hemispheric one. A detailed radiologic examination should be considered to delineate its neuroanatomic basis.