Oculomotor apraxia

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Oculomotor apraxia
Other namesCogan ocular motor apraxia or saccadic initiation failure
SpecialtyOphthalmology

Oculomotor apraxia (OMA) is the absence or defect of controlled, voluntary, and purposeful

vestibulo-ocular reflex. Patients have to turn their head in order to compensate for the lack of eye movement initiation in order to follow an object or see objects in their peripheral vision, but they often exceed their target. There is controversy regarding whether OMA should be considered an apraxia, since apraxia is the inability to perform a learned or skilled motor action to command, and saccade initiation is neither a learned nor a skilled action.[3]

Symptoms

  • Absence of fast phase nystagmus on horizontal optokinetic testing
  • Problems in nerve function involved in eye movement control, called
    neuropathy
  • Inability to visually follow objects
  • Head thrusts to compensate for the inability to accomplish voluntary horizontal gaze.[2][3]

Related developmental problems

Even though OMA is not always associated with developmental issues, children with this condition often have hypotonia, decreased muscle tone, and show developmental delays. Some common delays are seen in speech, reading and motor development.[3]

Causes

OMA is a neurological condition. Although some brain imaging studies of people with OMA reveal a normal brain, some MRI studies have revealed unusual appearance of some brain areas, in particular the corpus callosum, cerebellum, and fourth ventricle. Oculomotor apraxia can be acquired or

idiopathic.[1]

A person may be born with the parts of the brain for eye movement control not working, or may manifest poor eye movement control in childhood. If any part of the brain that controls eye movement becomes damaged, then OMA may develop.[2] One of the potential causes is bifrontal hemorrhages. In this case, OMA is associated with bilateral lesions of the frontal eye fields (FEF), located in the caudal middle frontal gyrus. The FEF control voluntary eye movements, including saccades, smooth pursuit and vergence. OMA can also be associated with bilateral hemorrhages in the parietal eye fields (PEF). The PEF surround the posterior, medial segment of the intraparietal sulcus. They have a role in reflexive saccades, and send information to the FEF. Since the FEF and PEF have complementary roles in voluntary and reflexive production of saccades, respectively, and they get inputs from different areas of the brain, only bilateral lesions to both the FEF and PEF will cause persistent OMA. Patients with either bilateral FEF or bilateral PEF damage (but not both FEF and PEF) have been shown to regain at least some voluntary saccadic initiation some time after their hemorrhages. Other causes of OMA include brain tumors and cardiovascular problems.[4][5]

Ataxia with oculomotor apraxia

A subgroup of genetically recessive

ataxia telangiectasia. These are autosomal recessive disorders and the associated gene products are involved in DNA repair. Both horizontal and vertical eye movements are affected in these disorders.[3] Although people with either type may have some mild cognitive problems, such as difficulty with concentration or performing multi-step activities, intellectual function is usually not affected.[6]

Type 1

Ataxia-oculomotor apraxia type 1 (AOA1) usually has an onset of symptoms during childhood. It is an autosomal recessive cerebellar ataxia (ARCA) associated with hypoalbuminemia and hypercholesterolemia. Mutations in the gene

APTX, which encodes for aprataxin, have been identified to be responsible for AOA1. Elevated creatine kinase is occasionally present, in addition to a sensorimotor axonal neuropathy, as shown by nerve conduction velocity studies. In addition, MRI studies have shown cerebellar atrophy, mild brainstem atrophy, and, in advanced cases, cortical atrophy.[7]

The aprataxin protein APTX can remove obstructive termini from DNA strand breaks that interfere with

neurodegenerative agents in AOA1 patients that lack functional aprataxin protein. However, single-strand breaks with 5'-AMP termini appear to be the most likely candidate lesion.[8]

Type 2

Ataxia-oculomotor apraxia type 2 (AOA2), also known as spinocerebellar ataxia with axonal neuropathy type 2,

Purkinje cells, and demyelination. In particular, there is a failure of the cerebrocerebellar circuit in AOA2 that has been shown to be responsible for the weaker coordination of complex cognitive functions such as working memory, executive functions, speech, and sequence learning.[6] Although there is no sign of mental retardation or severe dementia, even after long disease duration, research on families with possible AOA2 have shown mild cognitive impairment as indexed by the mini–mental state examination (MMSE) and the Mattis dementia rating scale. These impairments appear to be mostly due to a deficit in initiation and concept subtests.[10][11]

Ataxia telangiectasia

Ataxia telangiectasia results from defects in the ataxia telangiectasia mutated gene, which can cause abnormal cell death in various places of the body, including brain areas related to coordinated movement of the eyes. Patients with ataxia telangiectasia have prolonged vertical and horizontal saccade latencies and hypometric saccades, and, although not all, some patients show head thrusts.[3][10][12]

Diagnosis

References

  1. ^
    PMID 20687492
    .
  2. ^
    S2CID 29587221
    .
  3. ^ a b c d e Galvaez-Jimenez N, Tuite P, Bhatia K, editors. Uncommon Causes of Movement Disorders. New York: Cambridge University Press; 2011:38-40.
  4. S2CID 207005510
    .
  5. S2CID 31344729
    .
  6. ^
    S2CID 24521188
    .
  7. ^ Tarsy, D. editor. Movement Disorders: a video atlas. New York: Humana Press; 2012:28-29.
  8. ^
    PMID 21550379
    .
  9. ^ Spinocerebellar ataxia with axonal neuropathy type 2 Orphanet. Retrieved 28 December 2019
  10. ^
    PMID 23015802
    .
  11. PMID 14736755
    .
  12. PMID 22345219
    .
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