Accuracy of CT scan measurements of the medial temporal lobe in routine dementia diagnostics.

BACKGROUND

Atrophy of the medial part of the temporal lobe is seen in Alzheimer's disease (AD). We studied the usefulness of CT scan measurements of the medial temporal lobe (MTL) in elderly with suspected dementia.

METHODS

MTL measurements were done with callipers by three raters, blinded to the diagnosis and to each other, on scans from 110 subjects with suspected dementia from a memory clinic in Oslo, Norway and 36 participants included in the OPTIMA study, Oxford, England.

RESULTS

The correlation between the MTL and the Mini-Mental State Examination (MMSE) was very low, and there was a marked overlap between Alzheimer and cognitively unimpaired subjects. The inter-rater reliability was lower on the Norwegian than on the OPTIMA scans (R = 0.48 vs R = 0.68), but this was partly explained by larger MTL readings (4.5 mm after adjustment for age, gender and MMSE sumscore) on the OPTIMA scans as the reliability was confounded by MTL width and was higher at larger MTLs. A wider scan width (3 mm vs 2 mm in the OPTIMA scans) can also contribute to differences in reliability.

CONCLUSIONS

The published threshold values regarding the CT scan MTL measurements for the diagnosis of AD may be invalid when applied by other radiology departments without a local standardisation and validation.