How is sporadic olivopontocerebellar atrophy (OPCA) classified?

Updated: Dec 17, 2018
  • Author: Sombat Muengtaweepongsa, MD, MSc; Chief Editor: Selim R Benbadis, MD  more...
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Finally, the sporadic OPCAs are considered. According to current knowledge, sporadic cases can be classified into the 3 following categories, which may be modified later based on further research findings:

  • Type 1 - A subtype; essentially the presentation of MSA

  • Type 2 - Sporadic cases that are not part of an MSA, as presently understood

  • Type 3 - De novo mutations that are actually genetic cases (but authorities do not realize they are genetic)

A separate but related question is whether the sporadic diseases are simply multigenetic, with the genetics being presently too complex to recognize as such.

A large percentage of the sporadic OPCAs are a subset of MSA, known as cerebellar subtype (MSA-C). Some authorities have claimed that all sporadic OPCAs will progress to include significant autonomic and parkinsonian features and thus evolve into full-blown MSA if the patient lives long enough. According to this view, MSA typically starts as an ataxic OPCA form, an autonomic form (Shy-Drager syndrome), or a parkinsonian form (striatonigral degeneration). Motor neuron degeneration with spasticity and pyramidal weakness, and dementia also eventually occur. [11]

However, a large and careful study by Gilman et al published in 2000 showed that of the cases they selected for analysis, only 25% of the sporadic OPCAs converted to full-blown MSA within 5 years. [12] Nevertheless, all the sporadic OPCAs, Shy-Drager syndrome, striatonigral degeneration, and full-blown MSAs appear on the molecular level to be alpha-synucleinopathies; that is, they involve abnormalities of the protein alpha-synuclein. In addition, Jellinger reports in 2003 that the molecular pathology involves alpha-synuclein–positive glial (and less abundant neuronal) cytoplasmic inclusions in MSA and in all the purported subtypes. [13] These inclusions are also different from the alpha-synucleinopathic inclusions (eg, Lewey bodies), which are seen in other diseases.

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