Delayed saccadic initiation, oculomotor apraxia, could be an early presentation of juvenile-onset Huntington disease (juvenile HD), according to a case report published in Movement Disorders Clinical Practice. Oculomotor apraxia has been reported in about 20% of juvenile HD cases, but it usually occurs later in the disease progression.
The patient in the case report, a 16-year-old male, first presented with oculomotor apraxia at 14 years of age. He failed to start voluntary saccades and upward gaze palsy, often attempting to utilize blinking or head thrusts to initiate eye movements. He also presented with dysarthric speech and mild cerebellar ataxia.
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Assessment 3 months after the initial presentation revealed new findings of bradykinesia with preserved reflexes and strength and hypertonia with rigidity. Dystonic posturing of the limbs and trunk, along with difficulties turning, were identified through gait analysis.
The patient had a normal birth and early development but began to experience recurrent falls at age 13. He also had regression of gross motor skills and coordination, leading to withdrawal from sports. Fine motor tasks were difficult for him, and his peers noticed it was difficult for him to “move his eyes.”
Oculomotor apraxia, along with the above parkinsonism and dystonia motor symptoms, could be indicative of several disorders, including ataxia with oculomotor apraxia 2 (AOA2), Kufor-Rakeb disease, ataxia telangiectasia (AT), Niemann Pick Type C, and PLA2G6-or GNB1-associated movement disorders.
Further testing revealed normal urine metabolic screen, nerve conduction studies, and cerebrospinal fluid tests. MRI scans of the brain, which were initially reported as normal from a referring rural hospital, were found to have bilateral neostriatal hyperintensity and atrophy in the presence of normal appearances for the cerebellum and brainstem. Triplet repeat testing identified a CAG expansion 74 in the HTT gene, consistent with juvenile-onset HD.
At age 16, the patient has now progressed with impaired bulbar function, rigidity, bradykinesia, spasticity with brisk reflexes, and dystonia. He also progressed to ophthalmoplegia and has limited gait with primary mobilization utilizing a manual wheelchair.
“In summary, oculomotor apraxia with parkinsonian features in a teenager should alert the clinician to considering juvenile HD as a differential,” the authors wrote.
“Trinucleotide repeat testing is a key investigation, as repeat expansions are not evaluated on microarray or whole exome-based testing, though whole genome sequencing has shown high sensitivity and specificity in identifying them in neurological disorders,” the authors continued.
Innes EA, Qiu J, Morales-Briceño H, Farrar MA, Mohammad SS. Oculomotor apraxia as an early presenting sign of juvenile‐onset Huntington’s disease. Mov Disord Clin Pract. Published online August 24, 2023. doi:10.1002/mdc3.13775