Olivopontocerebellar Atrophy Workup

Updated: Nov 11, 2014
  • Author: Christina J Azevedo, MD; Chief Editor: Selim R Benbadis, MD  more...
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Workup

Laboratory Studies

Anti-Purkinje cell antibodies: Paraneoplastic cerebellar degeneration is an important entity in the differential diagnosis. Ovarian cancer is one of the malignancies associated with this syndrome, and the paraneoplastic syndrome may manifest in the early and curable stage of cancer. Anti-Purkinje cell antibodies are the diagnostic marker for this entity, and an assay for these antibodies is commercially available. If the patient is a female who has not had oophorectomy and if the degenerative disorder is sporadic rather than clearly familial, additional screening for ovarian cancer is appropriate. Small cell cancer of the lung is also associated with this syndrome.

Vitamin E level: Although isolated vitamin E deficiency is exceedingly rare, the serum vitamin E level should be measured as part of the diagnostic workup.

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Imaging Studies

MRI is the imaging study of choice in patients with olivopontocerebellar atrophy (OPCA) because CT scanning does not provide adequate resolution of the pons and cerebellum. MRI typically shows (1) pancerebellar and brainstem atrophy, with flattening of the pons; (2) an enlarged fourth ventricle and cerebellopontine angle; and (3) demyelination of the transverse pontine fibers. This demyelination of the transverse pontine fibers is responsible for the "hot cross bun" sign, which is thought to be highly specific for multiple system atrophy.

In the first year after the onset of cerebellar symptoms in patients with OPCA, MRIs may be normal; therefore, serial MRI examinations are necessary for detecting infratentorial atrophy.

Brain MRI is also useful in patients presenting with spinocerebellar syndromes to exclude the diagnoses of multiple sclerosis, cerebrovascular disease, and malignancy.

MRI also permits visualization of pontine atrophy, which distinguishes OPCA from other forms of genetic ataxias, and presentations of multiple system atrophy that do not yet heavily involve the pons.

MR SPECT has been used in case reports and shows a decreased NAA/Cr ratio consistent with atrophy. The clinical use of this is not yet defined. [112]

Positron emission tomography (PET) scanning shows reduced metabolism in the brain stem and cerebellum. While this finding is of academic interest, PET scanning is not necessary for the diagnostic workup of a patient with OPCA, and the results do not distinguish subtypes of OPCA.

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Other Tests

Table 3 in Causes lists whether genetic tests are available for the particular SCA. At present, commercial tests are available for SCA-1 (OPCA-I and OPCA-IV), SCA-2 (OPCA-2), SCA-3 (Machado-Joseph disease, not an OPCA), SCA-7 (OPCA-III), SCA-8 (an ADCA-1 but not an OPCA), SCA-10 (an ADCA-3, not an OPCA), SCA-12 (not an OPCA), SCA-14 (not an OPCA), SCA-17 (may be OPCA-V), and DRPLA (not an OPCA). In addition, a research test may be available for some others, such as episodic ataxia type 1, which is a dominant ataxia that is not an OPCA. Table 3 also provides the relevant chromosome and literature reference to the gene involved.

Sleep studies reveal lack of rapid eye movement and stage IV sleep in patients with OPCA. Apneic periods have also been observed.

Nerve conduction studies reveal a sensory neuropathy greater than motor neuropathy.

Evoked potentials may be delayed, especially visual evoked potentials.

EEG may show diffuse slowing and background disorganization.

None of the studies mentioned is necessary for the diagnostic workup of every patient with a progressive spinocerebellar syndrome.

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Histologic Findings

Histologic findings vary among the subtypes of OPCA. The cerebellum shows predominant Purkinje cell loss. Sometimes, Purkinje cells are completely obliterated. Purkinje cell axon torpedoes are variably present. The molecular and granular layers are usually thin. The cerebellar white matter is depleted. The pons exhibits loss of transverse pontine fibers and pontine nuclei. Fibrous gliosis exists in the spaces created by the loss of fibers. Preolivary medullary fibers are reduced, and the arcuate nuclei may be so atrophic that they cannot be found. Some patients demonstrate olivary hypertrophy.

Degeneration of the dorsal columns and neuronal loss in the Clarke columns are present. In addition, dorsal root ganglia and anterior horn cells may be reduced.

Argyrophilic oligodendroglial cytoplasmic inclusions, which under light microscopy may resemble neurofibrillary tangles, are present in sporadic forms of OPCA. These typically contain alpha-synuclein.

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Staging

A staging system specific to OPCA is not available.

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