BY CorTechs LabsMarch 18, 2020

Hippocampal Occupancy Score (HOC): Predicting the Progression of MCI to Alzheimer’s

The NeuroQuant Age Related Atrophy report includes a hippocampal occupancy (HOC) score along with volumes of the hippocampi and inferior lateral ventricles, which are important biomarkers used in the assessment of patients with MCI and Alzheimer’s Disease. As with all NeuroQuant reports, the brain structure volumes and HOC are normalized to intracranial volume (ICV) and compared to healthy patients of the same age and sex.

Current research has demonstrated the effectiveness of the HOC in assessing patient progression from mild cognitive impairment (MCI) to Alzheimer’s disease (AD). This proven biomarker is an invaluable factor in predicting the progression of neurodegenerative diseases as approximately 10 – 15% of all patients diagnosed with MCI will develop AD annually [1]. Hippocampal volume remains the best single predictor of conversion of MCI to AD at a 3-year follow-up [2].

The HOC measures the degree of hippocampal atrophy accounting for volume loss and compensatory inferior lateral ventricle (ILV) expansion. It is calculated as a ratio of hippocampal volume to the sum of the hippocampal and ILV volumes in each hemisphere separately, which are then averaged and normalized for age and sex. The equation is as follows:

The NeuroQuant Age Related Atrophy report provides the HOC in the first row of the table below the segmented images. The HOC is then visualized on the graph below the table to the far left, where it is plotted against the age and sex normalized values. The normative range (5th – 95th percentile) is represented in the white area of the graph while the solid line represents the mean. 

Below are a few examples to better illustrate how the HOC is interpreted with the rest of the information provided on the NeuroQuant Age Related Atrophy report.

Example Cases

Case 1: 

 

  • 67-year-old male – two time points
  • HOC is .69 cm3 within the normative range for age and sex.
  • Normal volumes: The hippocampi, lateral ventricles, and inferior lateral ventricles are within the normative range for age and sex.
  • Conclusion: Normal follow up that does not support neurodegeneration or the progression from MCI to AD. 

 

Case 2:

 

  • 36-year-old female – single time point
  • HOC is 0.66 cm3. The mesial temporal lobe is more than 2 standard deviations from the normative range for age and sex. 
  • Low volume: The hippocampi demonstrate atrophy, beyond 2 deviations below the normative range for age and sex.
  • High volume: The lateral ventricles and inferior lateral ventricles are enlarged beyond 2 standard deviations above the normative range for age and sex.

Conclusion: Low hippocampal volume and suggestive of local ex-vacuo dilatation. This supports mesial temporal lobe-focused neurodegenerative etiology. Suggestive of the progression from MCI to AD.

 

This measure not only aids in the differentiation of individuals with congenitally small hippocampi from those with small hippocampi due to a degenerative disorder but also effectively demonstrates the risk of conversion from MCI to AD. 

Citations:

[1] Biomarkers for the clinical evaluation of the cognitively impaired elderly: amyloid is not enough

[2] Predictive Utility of Marketed Volumetric Software Tools in Subjects at Risk for Alzheimer Disease: Do Regions Outside the Hippo

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