Disconnections in Infantile-Onset Saccade Initiation Delay: A Hypothesis

Infantile-onset saccade initiation delay (congenital ocular motor apraxia)

Infantile-onset saccade initiation delay, also known as congenital ocular motor apraxia, typically presents in early infancy with horizontal head thrusts once head control is achieved. Defective initiation of horizontal saccades and saccade hypometria with normal saccadic velocity are characteristic findings. Isolated impairment of vertical saccades is rare. Impaired smooth ocular pursuit may be seen. Other relatively common features include developmental delay, hypotonia, ataxia, or clumsiness. Brain MRI may be normal or show a diverse range of abnormalities, most commonly involving the cerebellum. Defective slow phases of the optokinetic response are commonly associated with brain MRI abnormalities. Isolated defect of vertical saccade initiation may indicate supratentorial brain abnormalities on MRI. Joubert syndrome, a developmental midbrain-hindbrain malformation, and ataxia telangiectasia are both commonly associated with defective volitional and reflexive saccade initiation, saccade hypometria, and head thrusts. Both horizontal and vertical saccades are impaired in these two disorders.

Do the clinical features in infantile-onset saccade initiation delay (congenital ocular motor apraxia) correlate with brain magnetic resonance imaging findings?

BACKGROUND

Infantile-onset saccade initiation delay (ISID) is a defect in saccade initiation. Other features may include impaired smooth ocular pursuit, developmental delay, hypotonia, and ataxia. Brain magnetic resonance imaging (MRI) can be normal or show supratentorial or infratentorial abnormalities. Our aim was to correlate the clinical features of ISID with brain MRI findings.

METHODS

Detailed review of the English medical literature between 1952 and 2012 revealed 67 studies with possible ISID. Patients without a brain MRI or with inadequate information, Joubert syndrome, neurodegenerative disorders, and acquired saccade initiation delay were excluded. Ninety-one patients (age range, 3 months to 45 years) met the inclusion criteria and were divided into 3 groups based on their brain MRI findings: normal (n = 55), supratentorial abnormalities (n = 17), and infratentorial abnormalities (n = 19). The patients' clinical features including the direction of head thrusts, smooth pursuit, optokinetic response (OKR), tone, development, and coordination were compared and analyzed among the MRI groups using χ test.

RESULTS

Horizontal head thrusts were significantly more common in patients with infratentorial abnormalities or normal brain MRI, whereas vertical head thrusts were more common among patients with supratentorial abnormalities (P < 0.0001). The slow phases of the OKR were significantly more likely to be impaired in patients with supratentorial or infratentorial abnormalities than in those with a normal MRI (P = 0.011). Other neuro-ophthalmological, neurological, and developmental features were similar among patients in the 3 neuroimaging groups.

CONCLUSION

The direction of head thrust and the integrity of the slow phases of the OKR are useful clinical indicators of possible sites of abnormality on brain MRI in patients with ISID.

The syndrome of infantile-onset saccade initiation delay

INTRODUCTION

Infantile-onset saccade initiation delay (ISID), also known as congenital ocular motor apraxia, is characterized by the inability to initiate volitional horizontal saccades. Other abnormalities including developmental delay and ataxia have been reported. The frequency of these abnormalities is unknown. We performed a detailed review of the medical literature to quantify features of ISID.

METHODS

We searched the English medical literature for articles related to ISID from 1952 to 2010. Whenever possible, patients were excluded if they had acquired SID, Joubert syndrome or neurodegenerative conditions. The minimum prevalence was calculated for each abnormality.

RESULTS

Sixty-six articles with information on 288 patients were included in the analysis. Head thrusts were reported in 84.7%. Blinks without head thrusts were used to initiate saccades in 41%. The fast phases of the optokinetic response and vestibulo-ocular reflex were impaired in 69.8% and 34.4% respectively. Smooth ocular pursuit was abnormal in 33%. Global developmental delay occurred in 41.3%, speech or language delay in 36.5%, cognitive delay in 17%, hypotonia in 35.8%, motor delay in 48.6%, and ataxia/clumsiness in 49.3% of patients. Neuroimaging was performed on 197 patients and was normal in 39.1%. Abnormalities involved the cerebellum (24.9%), cerebrum (15.7%), other infratentorial structures (11.7%), and corpus callosum (6.1%).

CONCLUSIONS

Infantile-onset saccade initiation delay is frequently associated with deficits in reflexive saccades and less frequently with impaired smooth ocular pursuit. Developmental delay, hypotonia, and ataxia occur frequently in ISID, suggesting more global brain impairment and not just a saccadic disorder.