Eye Movements May Help Detect Inborn Errors of Metabolism Early in Disease

Eye movement examinations may help detect inborn errors of metabolism (IEMs) in patients with unexplained movements disorders and/or psychiatric symptoms, according to study findings presented at the International Congress of Parkinson’s Disease and Movement Disorders (MDS) Virtual Congress 2021, held from September 17 to 22, 2021.

Movement disorders and psychiatric symptoms are the most commonly presenting symptoms in late-onset forms of IEMs. While eye movement abnormalities are reported in certain IEMs, the authors of the current study explained that they are often overlooked in clinical practice.

The objective of the study was to assess eye movements in patients with IEMs and when they present during disease course.

Researchers performed a standardized, videotaped neurologic examination and video-oculography to assess eye movements in 37 patients. Patients had 15 different IEMs, ranging from mitochondrial disease to Niemann-Pick type C. The most frequent movement disorders identified in the cohort included dystonia (77%), ataxia (60%), and myoclonus (40%). A total of 14 patients presented with a history of psychiatric symptoms.

The researchers noted that eye movement abnormalities were an early feature in at least 14 patients. Some of the abnormalities were found for specific types of IEMs, including vertical supranuclear gaze palsy in Niemann-Pick type C (n=10) and a progressive external ophthalmoplegia in mitochondrial disease (n=1).

In contrast, the remaining patients had abnormalities on video-oculography that were largely heterogeneous. The eye movement abnormalities detected in the population were saccadic oscillations (70%), nystagmus (16%), abnormal saccades (52%), impaired smooth pursuit (73%), impaired optokinetic nystagmus (56%), and eye movement abnormalities during hyperventilation (32%). Researchers also detected index eye movement disorders in individuals who had Krabbe disease, metachromatic leukodystrophy, and methylmalonic acidemia.

“Eye movement disorders may be present early in disease, not only in IEM known to be associated with eye movement disorders,” the researchers explained, yet “with a few exceptions, the type of eye movement disorder does not point in the direction of specific IEM.”

Reference

Koens LH, de Koning TJ, Tijssen MAJ. Eye movement disorders in adolescents and adults with an inborn error of metabolism. Presented at: MDS Virtual Congress 2021; September 17-22, 2021. Abstract 1173.