52. Downbeat Nystagmus & the Hereditary Ataxias

Anatomy: Pons, medulla, foramen magnum, posterior fossa. Pathology: Posterior fossa lesion, foramen magnum lesion, purkinje cell abnormality in cerebellum. Disease/Diagnosis: Familial or progressive spinocerebellar ataxia. Clinical: 1. Vertical downbeating nystagmus is a hallmark of foramen magnum lesion. 2. Cogan drop test - a test for corneal sensation and thus first division of 5th cranial function. 3. Ataxia telangiectasia. On eye examination one can see telangiectasia in lower tarsal region, fornix, ears and nose. The patient may have an ocular motility dysfunction including pseudo ophthalmoplegia, pseudo progressive supranuclear palsy, and one-and-a-half syndrome. These patients may have macular edema or degenerative retinitis pigmentosa. 4. Fredericks ataxia: It typically effects children under 20 years of age who may have pes cavus deformity, dysarthria, nystagmus, kyphosis, scoliosis, ataxia, and depressed knee and ankle jerk, may have cardiomyopathy and optic atrophy with or without retinitis pigmentosa.