Symptoms and signs may include gait impairment, visual blurring due to nystagmus, unclear (“scanning”) speech, hand incoordination, and tremor with movement. Differential diagnosis: Unsteady gait associated with vertigo from vestibular nerve or labyrinthine disease can resemble gait instability of cerebellar disease but produces a perception of movement, dizziness, or light-headedness. Sensory disturbances also can simulate cerebellar disease; with sensory ataxia, imbalance dramatically worsens when visual input is removed (Romberg sign). Bilateral proximal leg weakness also can rarely mimic cerebellar ataxia.
| APPROACH TO THE PATIENT | ||
AtaxiaCauses are best grouped by determining whether ataxia is symmetric or focal and by the time course (Table 187-1 Etiology of Cerebellar Ataxia). Also important to distinguish whether ataxia is present in isolation or is part of a multisystem neurologic disorder. Acute symmetric ataxia is usually due to medications, toxins including alcohol, viral infection, or a postinfectious syndrome (especially varicella). Subacute or chronic symmetric ataxia can result from hypothyroidism, vitamin deficiencies, infections (Lyme disease, tabes dorsalis from syphilis, prions), alcohol, other toxins, or an inherited condition (see below). An immune-mediated progressive ataxia is associated with antigliadin antibodies; biopsy of the small intestine may reveal villous atrophy of gluten enteropathy. Elevated serum anti-glutamic acid decarboxylase (GAD) antibodies have been associated with a progressive ataxic syndrome affecting speech and gait. Progressive nonfamilial cerebellar ataxia after age 45 suggests a paraneoplastic syndrome, either subacute cortical cerebellar degeneration (ovarian, breast, lung, Hodgkin's) or opsoclonus-myoclonus (neuroblastoma, breast, lung). Unilateral ataxia suggests a focal lesion in the ipsilateral cerebellar hemisphere or its connections. An important cause of acute unilateral ataxia is stroke. Mass effect from cerebellar hemorrhage or swelling from cerebellar infarction can compress brainstem structures, producing altered consciousness and ipsilateral pontine signs (small pupils, sixth or seventh nerve palsies) sometime without prominent limb ataxia; prompt surgical decompression of the posterior fossa can be lifesaving. Other diseases producing asymmetric or unilateral ataxia include tumors, multiple sclerosis, progressive multifocal leukoencephalopathy (in immunodeficiency states), and congenital malformations. |
May be autosomal dominant, autosomal recessive, or mitochondrial (maternal inheritance); >30 disorders recognized. Friedreich's ataxia is most common; autosomal recessive, onset before age 25; ataxia with areflexia, upgoing toes, vibration and position sense deficits, cardiomyopathy, hammer toes, scoliosis; linked to expanded trinucleotide repeat in the intron of gene encoding frataxin; a second form is associated with genetically determined vitamin E deficiency syndrome. Most common dominantly inherited ataxias are spinocerebellar ataxia (SCA)1 (olivopontocerebellar atrophy; “ataxin-1” gene) (Fig. 187-1. Sagittal Magnetic Resonance Imaging (MRI) of the Brain of a 60-Year-Old Man with Gait Ataxia and Dysarthria due to Spinocerebellar Ataxia Type 1 (Sca1), Illustrating Cerebellar Atrophy (Arrows)), SCA2 (ataxin-2; pts from Cuba and India), and SCA3 (Machado-Joseph disease); all may manifest as ataxia with brainstem and/or extrapyramidal signs; SCA3 may also have dystonia and amyotrophy; genes for each disorder contain unstable trinucleotide repeats in coding region.
Diagnostic approach is determined by the nature of the ataxia (Table 187-1 Etiology of Cerebellar Ataxia). For symmetric ataxias, drug and toxicology screens; vitamin B1, B12, and E levels; thyroid function tests; antibody tests for syphilis, Lyme, and Legionella infection; antigliadin and anti-GAD antibodies; paraneoplastic antibodies (Chap. 79 Neurologic Paraneoplastic Syndromes); and CSF studies often indicated. Genetic testing is available for many inherited ataxias. For unilateral or asymmetric ataxias, brain MRI or CT scan is the initial test of choice; CT is insensitive for nonhemorrhagic lesions of the cerebellum.
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Ataxia
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