What is the Difference between Nystagmus and Ocular Motor Apraxia?

Patient Presentation
A 20-month-old male came to clinic with a gradual onset over at least 1 month of head-tilting in different directions throughout the day. He also had eye movements that were described as both eyes turning laterally slowly and then coming back centrally quickly. These movements could also be in other directions, but the movements were not described as rotary. Both the head-tilting and eye movements appeared together, and were increasing in the number of episodes. Daycare providers and other parents also noted the abnormal movements. His mother denied other strange posturing or movements of the limbs, trunk, face or vocalizations. She said that he did not seem clumsier with walking or fine motor movements. It was worse when he was crying, angry or when needing to visually fix on an object. For example, when feeding himself his head would tilt and eyes dart when scooping food, but he was able to easily move the spoon to his mouth. He had a URI infection about 2 weeks before the onset of symptoms. The past medical history was negative with slower language milestones being met but within normal range. There were no developmental milestone loss. The family history was negative for neurological, genetic and opthalmological disease. The father had some problems with school but finished with average grades and received his associate’s degree. The review of systems was negative including fever, headache, weight loss, other eye changes or rashes.

The pertinent physical exam showed a healthy appearing male with growth parameters in the 50-90%. HEENT showed pupils equal, round and reactive to light and accommodation. Lateral eye nystagmus was noted to the right and left that occurred with head tilting laterally or downward. head-tilting appeared to occur more with object fixation. Red reflexes were present bilaterally and symmetric but fundus examination could not be accomplished. Neurological examination showed cranial nerves intact, with normal muscle tone, strength and bulk. No truncal ataxia was noted, nor ataxia with walking. He was able to accurately pickup and place small objects with a pincer grasp. Deep tendon reflexes were normal. Skin examination was normal as was the rest of his examination. The differential diagnosis at this time included a visual abnormality, tics, pediatric autoimmune neuropsychiatric disorder associated with streptococcal infection (PANDAS), tumor of visual axis or central nervous system or occult neuroblastoma, and accidental poisoning. The work-up included a negative anti-streptolysin O, brain magnetic resonance imaging, 24 hour urine testing for VMA/HVA, and urine drug testing. A pediatric neuroophthalmologist was available and felt this was most consistent with the diagnosis of oculomotor apraxia with some nystagmus. They recommended monitoring. One year later, the patient’s clinical course showed that the head tiling and eye movements had decreased, yet stereotypical oblique head movements remained. No nystagmus was seen at this examination, although it was described by the mother.

Discussion
Clinically, positive motor signs such as hypertonia, chorea, tics, and tremor are often easily to elicit. But negative neurological signs are more difficult to elicit and quantify.
These include:

• Weakness – “…the inability to generate normal voluntary force in a muscle or normal voluntary torque about a joint.” Weakness is usually present in many different postures, movements or tasks, but could be only seen in certain ones. Spinal muscle atrophy is one example.
• Reduced selective motor control – “…impaired ability to isolate the activation of muscles in a selected pattern in response to the demands of a voluntary posture or movement.” For example, a child with congenital mirror movements.
• Ataxia – “…inability to generate a normal or expected voluntary movement trajectory that cannot be attributed to weakness or involuntary muscle activity about the affected joints.” The path made by the movement is not expected. Walking in an undulating or inconsistent pattern is one example.
• Apraxia – “…impairment in the ability to accomplished previous learned and performed complex motor activities that is not explained by ataxia, reduced selective motor control, weakness or involuntary motor activity.” The inability is secondary.
  Developmental apraxia is the same as apraxia but is “…a failure to have ever acquired the ability to perform the age-appropriate complex motor actions.” This inability is primary, as the ability never was acquired.
  Ataxia is distinguished from apraxia and developmental apraxia in that the former’s deficits are not specific to particular tasks which the latter’s are.

Learning Point
Ocular motor apraxia (OMA) is a problem in the initiation of horizontal saccadic eye movement. Saccades are spontaneous, quick movements of both eyes in the same direction. Children with OMA use head thrusting to help their visual fixation. OMA usually has a good outcome with normal visual acuity and improvements in the head thrusting over time as the child grows older. OMA can be associated with other problems such as Ataxia-telangectasia, Ataxia associated with Ocular Motor Apraxia types 1,2,3, Gaucher Disease, and others.

Nystagmus is a rhythmic, involuntary movement of the eye. There are two general types. Jerk nystagmus when there is a slow phase movement in one direction, followed by a quick phase movement in the opposite direction. Pendular nystagmus has equal phases in both directions. There are many variations defined by the direction of the quick phase, periodicity, amplitude and waveform characteristics. They may be congenital or acquired.

With nystagmus, the muscle movement is involuntary and is present more consistently rather than intermittently. With apraxia the muscle movement is voluntary but there is a problem with performing this movement. For example, the eyes are trying to fixate on a target but may overshoot the target and then quickly return to the original or another position. The eyes may appear to have nystagmus-type movement but the child is moving the eye voluntarily. Because apraxia is voluntary, it is usually more intermittent.

Questions for Further Discussion
1. What are indications for consultation with a neurologist or opthalmologist?
2. What is included in the differential diagnosis for nystagmus?

Related Cases

Disease: Ocular Motor Apraxia| Neurologic Diseases

Symptom/Presentation: Nystagmus

Specialty: Neurology / Neurosurgery | Ophthalmology

Age: Infant

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Neurological Diseases

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

Rudolph CD, et.al. Rudolph’s Pediatrics. 21st edit. McGraw-Hill, New York, NY. 2003:2404-2406.

Palau F, Espinos C. Autosomal recessive cerebellar ataxias. Orphanet J Rare Dis. 2006 Nov 17;1:47.

Sanger TD, Chen D, Delgado MR, Gaebler-Spira D, Hallett M, Mink JW, Taskforce on Childhood Motor Disorders. Definition and classification of negative motor signs in childhood. Pediatrics. 2006 Nov;118(5):2159-67.

Liu W, Narayanan V. Ataxia with oculomotor apraxia. Semin Pediatr Neurol. 2008 Dec;15(4):216-20.

Online Mendelian Inheritance in Man. Ocular Motor Apraxia, MIM ID 257550. Available from the Internet at http://www.ncbi.nlm.nih.gov/omim/257550 (rev. 7/13/2010, cited 3/29/11).

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