In the ARCHIVES, Barbot et al1 report "ocular apraxia" in patients with autosomal recessive ataxia. The description of the disturbance is actually more compatible with supranuclear pseudo-ophthalmoplegia, which is characteristic of some autosomal dominant forms of spinocerebellar ataxia (SCA), especially SCA2 and SCA7. Many patients with Huntington disease have similar problems with ocular motility, and it is likely that the responsible anatomical lesion is located in the nucleus pontis centralis caudalis.2 Barbot and colleagues make no mention of the extensive descriptions of congenital and acquired ocular motor apraxia by Cogan3 and Cogan and Adams.4 These authors emphasized the definition of apraxia as a disorder only of willed movements, whereas random movements are preserved. Cogan and Adams found acquired ocular motor apraxia in 2 patients who had lesions of the cerebral hemispheres. Additional limb apraxia occurred in 1 patient who was suspected of having a postpartum superior sagittal sinus thrombosis. Autopsy confirmation of a metastatic tumor was obtained in the second patient. We reviewed the distinction between ocular motor apraxia and supranuclear ophthalmoplegia in a clinicoanatomic study of olivopontocerebellar atrophy that was later identified as SCA2.5 Neuronal loss in the paramedian pontine reticular formation may be responsible for the peculiar ocular disturbance in several hereditary and sporadic system disorders. They are quite subtle2 and are probably beyond the reach of current imaging techniques. Although the described disturbance is similar to true ocular motor apraxia, the term apraxia should be reserved for the rare defects that involve only voluntary (willed or willful) eye movements and spare random ones.
Koeppen AH. Ocular Apraxia in Recessive Ataxia. Arch Neurol. 2002;59(5):874. doi:
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