Investigators have discovered that adults with hypothyroidism are at an increased risk of suffering from abnormal regional brain metabolism and neuropsychological impairment.
"Hypothyroidism may profoundly alter mental function and influence mood and cognition, but the neural correlates of these impairments and of thyroid hormone treatment are not well understood," the researchers reported at the European Congress of Endocrinology in Glasgow, UK.
The team, led by M Bauer from the Charité University in Berlin, Germany, therefore compared the neuropsychiatric status and regional brain metabolism using position emission topography (PET) in 14 previously untreated hypothyroid patients and 10 euthyroid individuals, before and after thyroid replacement treatment with levothyroxine (L-T4). The participants were aged an average of 42 years.
Prior to treatment, the hypothyroid patients had significantly decreased glucose metabolism compared with the controls, particularly in the anterior and posterior cingulate cortex, the prefrontal cortex, and the subcortical structures including the dorsal and ventral striatum, the putamen, and the amgydala.
Treatment with L-T4 therapy, however, resulted in a significant increase of regional normalized brain activity in the hypothyroid patients, such that after treatment, no differences in brain metabolism were found between the patients and the controls.
L-T4 treatment was also effective in increasing prefrontal metabolism in the hypothyroid patients, which before treatment was decreased and correlated with the severity of somatic complaints.
This increase in the rate of prefrontal metabolism in the patients was associated with a normalization of thyroid-stimulating hormone levels and metabolism in the posterior cingulate cortex, which in turn led to an improvement in short-term memory.
Bauer told delegates: "This is the first PET study demonstrating in vivo regionally specific effects of primary hypothyroidism on cerebral glucose metabolism especially in the perigenual anterior cingulate/medial prefrontal gyrus and its normalization with L-T4 treatment.
"Furthermore, associations between abnormalities of regional brain metabolism and neuropsychological impairments can be demonstrated in adults with hypothyroidism."