Last week, we discussed that the patient’s mental state, fatigue, and a variety of medications can affect performance on oculomotor exams. Does this mean that we should dismiss abnormalities as irrelevant?
I got a question from a student a few years ago. She was curious what the referring physician would likely do after receiving a report that oculomotor performance was suggestive of cerebellar dysfunction. Of course, I can’t be sure how a particular physician would react, but I replied that they would most likely perform their own neurologic screening evaluation. If they saw any suggestions of cerebellar disease or other neurologic deficit, they would most likely refer to a neurologist or order neuro-imaging.
Stoddart et al (200) examined MRI findings in a group of patients considered to have evidence of central vestibular dysfunction on ENG exam. They found that only 30% of these patients had structural abnormalities on MRI that correlated with the abnormal ENG findings. They speculate that some central vestibular abnormalities may be functional, but not necessarily structural, or that related structural abnormalities were beyond the resolution capabilities of the MRI exam. They conclude that MRI and ENG are complementary in the diagnosis of central vestibular dysfunction, and do not provide redundant information. This is exactly how I describe the purpose of the oculomotor portion of the ENG exam: “MRI is a test to see if the part of the brain controlling balance looks normal. The oculomotor test is a test to see if it is functioning normally.”
Keeping all this in mind, when I dictate a report on a patient with abnormal oculomotor tests, I refer to it as “suggestive of possible cerebellar dysfunction” and suggest additional examination as the referring physician feels is warranted.