Cognitive and neuropsychiatric aspects of subclinical hypothyroidism: significance in the elderly.

The effects of overt hypothyroidism (HO) on cognition and mood are well established, and HO is considered a common cause of reversible dementia. There is now increasing evidence to suggest that subclinical hypothyroidism (ie, elevated thyroid stimulating hormone in the presence of normal thyroxine concentrations) may be a predisposing factor for depression, cognitive impairment, and dementia. Subclinical hypothyroidism is more common than HO and is most prevalent in the elderly, particularly in women. Older adults may be more vulnerable to the effects of subclinical hypothyroidism, given age-related changes to the hypothalamic-pituitary-thyroid axis, and there is an association between thyroid status and cognitive decline and dementia in the elderly. The purpose of this review is to summarize existing data on the cognitive and neuropsychiatric consequences of subclinical hypothyroidism, benefits of treatment, and recommendations for screening and monitoring in older adults.