Evaluation Guidelines Table173

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Neuroimaging. Immediate computerized tomography (CT) scanning or magnetic resonance imaging (MRI) has to be performed in the setting of acute and subacute cerebellar ataxia. Posterior fossa lesions (hemorrhage, ischemia, hydrocephalus, neoplasms, abscess, or parasitic infections) carry the risk of increased intracranial pressure and death because of the cerebellar tonsils moving downward and compressing the brain stem within the foramen magnum. Angiography of the vertebrobasilar vascular system should be performed if the diagnosis of an aneurysm, vascular malformation, or basilar artery thrombosis is suspected based on the findings of the CT or MRI scan.

Compared with CT scanning, MRI offers an increased capacity for demonstrating cerebellar (and brain stem) lesions because of a lack of bone artifact. MRI demonstrates cerebellar atrophy as well as spinal and brain stem involvement in degenerative cerebellar disorders. In addition, MRI is much more sensitive to white matter lesions, particularly demyelination. Therefore, MRI should be performed when multiple sclerosis is suspected.

Electrophysiology. Electrophysiological tests are applied to confirm extracerebellar lesions. Nerve conduction studies are performed when lesions of the peripheral nervous system are expected. Evoked potentials show lesions of the visual (visual evoked potentials), auditory (auditory evoked potentials), and somatosensory (somatosensory evoked potentials) systems. Involvement of the corticospinal tract is demonstrated using magnetic evoked potentials.

Fluid and Tissue Analysis. Intermittent ataxia associated with mental retardation and onset in infancy or early childhood suggests a metabolic disorder: for example, urea cycle deficiencies, aminoacidurias, and disorders of pyruvate and lactate metabolism. Screening investigations include blood ammonia, amino acids, urinary amino acids, pyruvate, and lactate.[6] Investigations of early-onset, chronic progressive ataxia associated with dementia should include blood ammonia, hexosaminidase, arylsulfatase A, galacto-cerebrosidase, amino acids, and bone marrow biopsy.

Metabolic disorders (e.g., lipid, mitochondrial and storage disorders, Refsum's and Wilson's diseases, hypothyroidism) should be excluded in early-onset chronic progressive ataxia and in adult-onset forms of the disorder, which are not dominantly inherited. Lipids, vitamin E, lactate, very long-chain fatty acids, adrenocorticotropic hormone (in males), phytanic acid, ceruloplasmin, and thyroxine should be analyzed. Alpha-fetoprotein is increased and immunoglobulins are decreased in ataxia-telangiectasia. A muscle biopsy should be performed in cases of suspected mitochondrial myopathy. Poisoning or drug intoxication has to be excluded. Anemia, macrocytosis, and raised gamma-glutamyltranspeptidase suggest alcoholic cerebellar degeneration. In children, neuroblastoma may be associated with paraneoplastic cerebellar degeneration leading to opsoclonus. Urinary catecholamine levels are increased. Diabetes mellitus should be excluded in Friedreich's ataxia. Genetic testing is available for an increasing number of inherited ataxias, particularly for autosomal dominant cerebellar ataxias with onset usually after the age of 20 years. y To date, direct DNA testing is available for spinocerebellar ataxia type 1 (SCA1) and type 3 (SCA3; Machado-Joseph disease), type 6 (SCA6), dentatorubral-pallidoluysian atrophy, and Friedreich's ataxia.

Cerebrospinal Fluid. Lumbar puncture and examination of the cerebrospinal fluid are applied when inflammatory or infectious disorders are expected. Pleocytosis, increased total protein content, and oligoclonal bands are found in patients with multiple sclerosis, viral cerebellitis, and paraneoplastic cerebellar disorders. In addition, serum and cerebrospinal fluid anti-Purkinje cell antibodies (anti-Yo, anti-Hu, and anti-Ri) are useful in the diagnosis of paraneoplastic cerebellar degeneration.y

Neuropsychological Tests. Degenerative forms of ataxia might be associated with dementia. Neuropsychological testing might be useful to confirm and quantify existing cognitive deficits.

Other Tests. Electronystagmography is a useful laboratory tool to confirm and quantify cerebellar oculomotor disorders. Posturography is applied to quantify ataxia of stance and to distinguish spinocerebellar, vestibulocerebellar, and spinal ataxias. Lesions of the anterior lobe lead to

TABLE 17-3 -- USEFUL STUDIES IN THE EVALUATION OF DISORDERS OF COORDINATION

Syndrome

Neuroimaging

Electrophysiology

Fluid and Tissue Analysis

Neuropsychological Tests

Other Tests

Truncal, gait and stance ataxia (absence of Romberg's sign)

CT or MRI: brain

Posturography ENG

CSF

N/A

N/A

Stance and gait ataxia (presence of Romberg's sign)

CT or MRI: brain

Posturography

Infancy and early childhood onset: Urinary catecholamine levels. Adult onset:

Anti-Purkinje cell antibodies, blood count, gamma-glutamyl transpeptidase.

CSF

N/A

Chest x-ray Pelvic imaging (to exclude malignancy)

Unilateral limb ataxia

CT or MRI: brain cerebral angiography

N/A

CSF

N/A

Truncal, cranial, and bilateral limb ataxia

CT or MRI: brain

Posturography, ENG, VEP, SSEP, AEP, MEP, NCVs

Infancy and early childhood onset:

Lipids, vitamin E, glucose, alpha-fetoprotein, immunoglobulins, VLCFA, ACTH (in males), lactate, ceruloplasmin, thyroxine.

Associated with dementia:

Hexosaminidase, arylsulfatase A, galactocerebrosidase, ammonia, amino acids, bone marrow biopsy.

Adult onset:

Lipids, vitamin E, VLCFA, ACTH (in males), lactate, ceruloplasmin, thyroxine.

CSF, genetic testing

N/A

Chest x-ray Electrocardiogram

Cerebellar speech

CT or MRI: brain

N/A

CSF

N/A

N/A

Paroxysmal ataxia

CT or MRI: brain

ENG, VEP, SSEP, AEP, MEP, NCVs

Infancy and early childhood:

Blood ammonia, pyruvate, lactate, amino acids, urinary amino acids.

Adult onset:

CSF

N/A

N/A

Cerebellar oculomotor signs

CT or MRI: brain

ENG

CSF

N/A

N/A

ACTH, Adrenocorticotropic hormone; AEP, auditory evoked potentials; CSE, cerebrospinal fluid; CT, computed tomography; ENG, electronystagmography; MEP, magnetic evoked potentials; MRI, magnetic resonance imaging; N/A, not applicable; NCVs, nerve conduction velocity studies; SSEP, somatosensory evoked potentials; VEP, visual evoked potentials; VLCFA, very long chain fatty acids.

anteroposterior body sway with a frequency of about 3 Hz. Lesions of the lower vermis cause omnidirectional postural tremor of head and trunk with frequency components below 1 Hz. Spinal ataxia leads to predominantly lateral body sway. [23]

In subacute-onset ataxia, a thoracic x-ray study and pelvic imaging are required to exclude malignancies (small cell lung cancer, ovarian or breast cancer, or Hodgkin's disease) causing paraneoplastic cerebellar degeneration. Abdominal and thoracic CT scan as well as bronchoscopy might be required. An electrocardiogram should be performed in Friedreich's ataxia, which might be associated with heart disease.

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