Pathogenesis and Pathophysiology. Idiopathic cerebellar ataxia (IDCA) refers to a heterogeneous group of nonhereditary degenerative ataxias that begin after the age of 25 years.y Ihe etiology of IDCA is unknown. Clinically and pathologically, there are two major types. Ihe cerebellar type, IDCA-C, is characterized by a purely cerebellar syndrome and an almost exclusive degeneration of the cerebellar cortex. Ihe plus type, IDCA-P, often has additional clinical features that suggest involvement of the basal ganglia, pyramidal tracts, and autonomic nervous system. y Pathologically, there are various combinations of OPCA, striatonigral degeneration, degeneration of the intermediolateral spinal columns, and Onuf's nucleus that qualify this disorder as the cerebellar type of multiple system atrophy (MSA-C). Ihe hypothesis that IDCA-P is part of the spectrum of MSA is supported by the observation that brains of patients with IDCA-P show MSA-typical oligodendroglial argyrophilic intracytoplasmic inclusion bodies. y Ihe etiology of both types of IDCA is unknown.
Epidemiology and Risk Factors. Ihere are no studies on the epidemiology and risk factors of IDCA.
Clinical Features and Associated Disorders. On average, IDCA starts around the age of 55 years. Both types, IDCA-C and IDCA-P/MSA are characterized clinically by a progressive cerebellar syndrome marked by ataxia of gait and stance, ataxia of limb movements, dysarthria, and cerebellar oculomotor abnormalities (gaze-evoked nystagmus, saccade hypermetria, broken-up smooth pursuit, reduced optokinetic nystagmus, and impaired suppression of vestibulo-ocular reflex by fixation). Saccade slowing never occurs in IDCA. Although the syndrome remains purely cerebellar in IDCA-C, patients with IDCA-P/MSA have additional noncerebellar symptoms, the most frequent of which are akinetic-rigid parkinsonism, pyramidal tract signs, bladder dysfunction, orthostatic hypotension, and
Figure 35-3 I2-weighted MRIs of the basal ganglia, pons, and middle cerebellar peduncles in IDCA-P/MSA, Hypointensities of basal ganglia. Upper left: Normal. Upper right: Hypointensity at the dorsolateral margin of the putamen in beginning IDCA-P/MSA. Lower left: Strong hypointensity extending through part of the body of putamen in IDCA-P/MSA. Lower right: Hypointensity extending throughout the putamen, with intensity exceeding that in globus pallidus in late-stage IDCA-P/MSA. Note the hyperintensity at the lateral putaminal borderB, Hyperintensities in the upper ponsleft side) and middle cerebellar pedunclefright side). Upper panel: Normal. Lower panel: Hyperintensities of the transverse pontine fibers between tegmentum and the base of p/eff) and in the middle cerebellar peduncles(right) in IDCA-P/MSA.
vocal cord palsy. These symptoms may be present years before any manifestation of ataxia, they may occur simultaneously with ataxia, or they may develop later. Male patients often have erectile dysfunction years before any neurological symptoms appear. y y y y
Differential Diagnosis and Evaluation. Xhe clinical phenotype of advanced IDCA-P/MSA, consisting of ataxia, parkinsonism, and autonomic failure, is highly characteristic and rarely causes confusion with other disorders. In contrast, IDCA-C and incomplete or beginning forms of IDCA-P/MSA must be carefully distinguished from symptomatic cerebellar ataxia. Degeneration of the cerebellar cortex in patients with chronic cerebellar ataxia may be due to alcoholism, various toxic causes (antiepileptics, cytostatic drugs, lithium, solvents, heavy metals), remote effects of malignancy (paraneoplastic cerebellar degeneration), malabsorption with vitamin E deficiency, increased body temperature (heat stroke, neuroleptic malignant syndrome, sepsis), and hypothyreosis.
Routine nerve conduction velocity and EMG studies in patients with IDCA give normal results in most cases. However, EMG of the external sphincter muscles is useful for distinguishing MSA from other disorders. Because of degeneration of Onuf's nucleus, external sphincter EMG reveals denervation activity and an increased number of polyphasic potentials.'«*1 Whether evoked potentials are helpful to distinguish MSA from IDCA-C has not been systematically explored. MRI of IDCA-C patients consistently shows pure cerebellar atrophy without brain stem or spinal cord involvement. Atrophy is often pronounced in the cerebellar vermis. Some IDCA-C patients have additional supratentorial atrophy. Patients with IDCA-P/MSA develop OPCA with diffuse cerebellar atrophy and additional shrinkage of the base of the pons and the middle cerebellar peduncles. In contrast to ADCA, the size of the cervical spinal cord remains normal (see Fig 35-2 ). T2-weighted images in patients with IDCA-P/MSA may show hypointense signals in the putamen, suggesting involvement of the basal ganglia. In addition, there are hyperintense areas in the pons and middle cerebellar peduncles, reflecting degeneration and gliosis of the pontocerebellar fibers( ..Fig 3.5:3 ). However, these are not early signs, and their absence does not exclude a diagnosis of IDCA-P/ MSA.y , y
Management. At present, there is no specific treatment for IDCA. As in other types of ataxias, a trial with 5-hydroxytryptophan, amantadine, or buspirone may be attempted, although there are no controlled trials that clearly demonstrate the efficacy of these drugs in relieving ataxia. Physical therapy is recommended. Many IDCA patients become dependent on canes or wheelchairs within years after the onset of disease. Additional noncerebellar symptoms in IDCA-P/MSA patients require adequate symptomatic treatment. Parkinsonian symptoms in these patients respond to dopaminergic medications, although the response is less robust than it is in patients with idiopathic Parkinson's syndrome. Many patients develop urinary retention and have to be supplied with suprapubic catheters. For management of orthostatic hypotension, elastic stockings and oral treatment with mineralocorticoids are recommended.
Prognosis and Future Perspectives. While IDCA-C patients have an almost normal life expectancy, the prognosis for those with IDCA-P/MSA is poor. Patients become wheelchair-bound approximately 5 years after the onset of disease. Median survival after disease onset is 8 to 10 years. y , 'asi Xhe cause of IDCA is unknown. Unlike the situation with the hereditary ataxias, major progress in understanding the pathogenesis of IDCA is not to be expected in the near future.
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