Evaluation of the memory function and cerebral blood flow in patients with hyperthyroidism

Objective: To assess the memory function of hyperthyroid patients at different disease durations and investigate the value of cerebral blood flow (CBF) imaging in the detection of memory dysfunction in related regions. Methods: Thirty-seven hyperthyroid patients (10 males, 27 females; mean age (39.27± 10.58) years) and 28 healthy volunteers (8 males, 20 females; mean age (35.80±9.41) years) were enrolled into this prospective study. The patients were divided into two subgroups: short duration group (duration ≤ 6 months; n=15), long duration group (duration >6 months ; n=22). Wechsler memory scale was used for memory assessment,and cancellation test was used for attention assessment.Self-rating depressions scale (SDS) and self-rating anxiety scale (SAS) were used for mood disorder assessment. ⁹⁹Tc^m-ECD SPECT CBF imaging was performed at rest for all patients and controls on the same day. SPM 2.0 was used to investigate the differences of rCBF between the two groups. Two independent samples t test was used for the comparisons of memory and attention scores between patients and controls, also between patients with short and long disease durations. Multiple stepwise regression was used for factor analysis of memory state. Results: Scale total score (92.27±17.50 vs 101.75±11.70; t=-2.476)and memory quotient (91.32±17.76 vs 100.29±9.43; t=-2.421) were significant different between patients and controls (both P<0.05). The scale total score and memory quotient in patients with long disease duration were significant lower than those of controls (88.77±16.69 vs 101.75±11.70, t=-3.231; 86.18±16.73 vs 100.29±9.43, t=3.770, both P<0.05). The memory quotient was significant lower in patients with long disease duration than those with short disease duration(86.10± 17.13 vs 98.87± 17.00; t=2.212, P<0.05). There was no significant difference in memory quotient and scale total score between short duration group and controls (t=-0.754, 0.910, both P>0.05). CBF was reduced in the limbic system of hyperthyroid patients and the involved area was larger in patients with long disease duration. Age, attention score,serum FT₄ level and reduced CBF in left pulvinar nuclei, left lateral geniculate body and right amygdale were the statistically significant factors for impaired memory function in hyperthyroid patients (b=-0.393-0.685, all P<0.05). Conclusions: Memory impairment could be significant in hyperthyroid patients with long disease duration. CBF imaging could reflect the degree of dysfunction at specific brain regions responsible for memory impairment in these patients. (authors)