Magnetic resonance parkinsonism index

Magnetic resonance parkinsonism index (MRPI) can be used in MRI studies to predict the presence of progressive supranuclear palsy (PSP) in patients with clinically unclassifiable parkinsonism.

MRPI is calculated by measuring the width of the superior cerebellar peduncle in the coronal plane, the middle cerebellar peduncle in the sagittal plane and the area of the midbrain and pons in the midsagittal plane. It is calculated by multiplying the pons area to midbrain area ratio by the middle cerebellar peduncle width to superior cerebellar peduncle width ratio 1-2:

(P / M) x (MCP / SCP)

  • MCP = width of middle cerebellar peduncle
  • SCP = width of superior cerebellar peduncle
  • P = area of pons in midsagittal plane
  • M = area of midbrain in midsagittal plane

A value of more than 13.55 indicates an abnormal result, and strongly suggests that these patients will go on to develop PSP. One study found that 78.5% of patients with clinically unclassifiable parkinsonism who had abnormal MRPI went on to fulfill criteria for PSP at two years following that measurement 2

NB: midbrain to pons area ratio has also been used to help in the diagnosis of PSP. 


Neurodegenerative diseases

Neurodegenerative diseases are legion and their classification just as protean. A useful approach is to divide them according to underlying pathological process, although even using this schema, there is much overlap and thus resulting confusion.

Article information

rID: 28173
Tag: psp
Synonyms or Alternate Spellings:
  • parkinsonism index
  • Magnetic Resonance Parkinsonism Index (MRPI)
  • MRPI

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Cases and figures

  • Figure 1: measures to calculate the MRPI
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