- You are evaluating a 4-year-old boy who complains of “bouncing eyes:’ His mother reports seeing his eyes jiggle for a few seconds at a time. There are no abnormal head, neck, trunk, or limb movements. He is awake during these episodes and complains that his eyes are “bouncing. ” On physical examination, the pupils are round and equally reactive to light, and eye movements are conjugate and intact in all directions. On downward gaze, there is downward nystagmus. The remainder of his physical examination findings, including hair and skin, are unremarkable
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.Of the following, the MOST likely diagnosis is
- A. Chiari I malformation
- B. congenital nystagmus
C. neurofibromatosis type 1
D. phenytoin ingestion
E. spasmus nutans - The boy described in the vignette has downbeat nystagmus, a subtype of vertical nystagmus. Vertical nystagmus is never normal and is usually the result of a brainstem abnormality. (Horizontal nystagmus can sometimes be normal, but a clinical evaluation is necessary, if it is a new finding.)
- In this case the most likely cause is a Chiari I malformation. Chiari I malformation is defined as the descent of the cerebellar tonsils at least 5 mm below the foramen magnum. Although Chiari I malformation is often an incidental finding, it can cause neurologic problems. Symptomatic Chiari I malformation can cause brainstem compression, which presents with dysphagia, dysarthria, upbeat or downbeat nystagmus, or limb weakness with hyperreflexia. Headache with Valsalva. maneuver (coughing, straining, or laughing, for example) can also be a symptom. Chiari I malformation can also be associated with spinal cord syrinx. In a clinically unstable patient, computed tomography of the head is the best test to evaluate for structural brain abnormality; in stable patients for whom magnetic resonance imaging is safe, this modality will yield greater information. The treatment for symptomatic Chiari I malformation is surgical decompression.
- Congenital nystagmus is present at birth and persists throughout life. The nystagmus is most often in the horizontal direction but can be vertical. No oscillopsia—the subjective sensation of objects moving in the visual field—is reported. Congenital nystagmus is often an isolated, benign finding, but can be associated with rare neurogenetic disorders such as Pelizaeus-Merzbacher disease or brain malformations.
Neurofibromatosis type 1 is associated with optic nerve gliomas and asymptomatic brain lesions, termed focal areas of signal abnormality, but neither of these cause downbeat nystagmus.
Phenytoin can cause horizontal nystagmus especially when given in high or loading doses. It does not cause vertical nystagmus. - Spasmus nutans, an idiopathic condition of infancy, is characterized by horizontal nystagmus, head tilting, and head nodding. It does not cause downbeat nystagmus. If the clinical diagnosis is uncertain, head and neck imaging should be performed to evaluate for structural abnormalities of the eye, brain, or neck.
Dr. Jayaprakash
Superintendent, ICH.
Institute of Child Health.
Gov. Medical College Kottayam.
Kerala, India.