From the case:
Magnetic resonance parkinsonism index
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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: (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
Case Discussion
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.
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