The relationship between white matter low attenuation on brain CT and vascular risk factors: a memory clinic study - computed tomography

Age and Ageing,  Sept, 1995  by Khaled Amar,  Tim Lewis,  Gordon Wilcock,  Margaret Scott,  Romola Bucks

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Table I. Demographic characteristics of the patients

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Table II shows that the prevalence of WMLA increases from 12% in patients who had no evidence of a cementing illness, to 32% in those with isolated memory loss and 59% in patients suffering from possible or probable dementia. Patients with high leucency score were also more likely to be suffering from dementia, especially vascular dementia, rather than isolated memory loss or no dementia.

Table II. Number (%) of patients in the different diagnostic
groups and the incidence of WMLA
                   No. of       WMLA
                 patients     present     LS> 4
All Dementias        127         76 (59)    19 (25)
Alzheimer's disease   76     40 (53)     7 (18)
Vascular dementia     33     23 (70)     7 (30)
AD and VAD             5      4 (80)     2 (50)
Other dementia        13      9 (69)     3 (33)
Possible dementia     17     10 (59)     0
Isolated memory loss  34     11 (32)     1 (9)
Normal                25      3 (12)     1 (33)
Total                202    100 (49.5)   21 (21)
LS > 4 = leucency score of 5 or 6.

There was no significant difference between patients with and without WMLA with regard to history of smoking, hypertension, diabetes, or hypercholesterolaemia and no correlation between WMLA and the blood glucose or cholesterol levels. However, as can be seen from Table III, raised systolic blood pressure, heart disease, peripheral vascular disease, focal neurological signs on examination and central atrophy were all significantly more common in patients with WMLA (p < 0.05).

Table III. Prevalence of vascular risk factors, findings on examination, blood results, and CT in patients with and without WMLA

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Although there were more visible cerebral infarcts on CT in the WMLA group, compared with patients with no visible WMLA, this did not reach statistical significance. The presence of central atrophy however was significantly more common in patients with WMLA and this remained even after including patients with both central and cortical atrophy. (p = 0.036).

On stepwise regression analysis, only age, diagnostic group and raised systolic blood pressure were predictors of WMLA When the effect of age was eliminated from the equation both diagnostic groups and raised systolic blood pressure remained as predictors of white matter lesions.

Discussion

The older age for the WMLA group is not surprising, since the prevalence of WMLA has been shown to rise with age [3, 4]. This age difference did not reach statistical significance in our sample (p = 0.067).

WMLA was commonest in patients with vascular and combined vascular and degenerative dementia as in previous reports [5, 7, 12]. The prevalence of WMLA in Alzheimer's disease (52%) was higher than that quoted in most similar studies and this may be explained, at least partially, by easier recognition of WMLA with more sensitive CT scanners. The high prevalence of white matter lesions (59%) recorded by Brun and Englund in their post-mortem studies of white matter changes in Alzheimer's disease suggests that this is not an overestimation [18]. Wallin et al. reported a marked difference in the prevalence of WMLA between early onset (onset before the age of 65 years) and late onset AD with a much higher frequency in patients with late onset AD (80% in late onset AD versus 11.5% in early onset AD) [12]. This was to an extent mirrored in our sample of patients with AD, i.e. among 76 AD patients, 22 patients had an early onset disease with a WMLA incidence of 36%, compared with a prevalence of 59% in 54 patients with late-onset disease. This trend was not statistically significant.