Oral temperature change and cognitive decline in Alzheimer's patients.

Abstract

To the Editor: May I offer a more prosaic explanation for the remarkable set of data that you published recently1 on the possible relationship between low core temperature and decline in mental status in Alzheimer's disease patients. A later comment on the findings2 noted that the decline in oral temperature was statistically significant (P < .001), whereas the decline in cognitive function was only marginally so (P = .06). If the oral temperature is taken to represent core body temperature in this study, then two of the 12 Alzheimer's patients would be regarded as clinically hypothermic (core temperature < 95.5°C) at the end of the study, and one other would be on the borderline of hypothermia. Oral temperature is a notoriously inaccurate measure of core temperature in cold ambient conditions and is often a spurious indicator of hypothermia. The question is, therefore, whether the difference between the first oral temperature reading and the second, taken 3 to 11 months later, reflected a seasonal drop in external temperature that affected the oral temperature readings. Oral temperatures were described as being measured in a standard outpatient setting, but equilibration of buccal cavity temperature may take considerable time in outpatients attending a clinic in winter. Therefore, details of the dates and environmental conditions would have been of value in interpreting the data. Perhaps it is not the absolute level of deep body temperature that is likely to provide a “prognostic and monitoring tool” in assessing Alzheimer's disease patients, but changes in circadian temperature rhythms in older people and in older Alzheimer's disease patients.3 It has been said that temperature rhythm variables are damped or phase shifted in Alzheimer's disease.4 This may, however, only apply to patients in the more advanced stages of the disease, for in carefully defined populations with mild Alzheimer's disease, no differences in temperature rhythms were found between patients and a healthy older control group.5 A method for measuring deep body temperature accurately that is unaffected by external temperature and is acceptable to patients on a 24 to 48 hour basis is a desirable, though surprisingly difficult, objective for monitoring Alzheimer's patients.