Neurological consequences of adult-onset hypothyroidism.

Adult-onset hypothyroidism has long been recognized as a reversible cause of cognitive impairment. However, recent studies have shown that it is associated with structural brain alterations besides functional alterations, particularly in the hippocampus and prefrontal cortex. Neurophysiological and molecular studies have demonstrated that hypothyroidism impairs synaptic plasticity, disrupts neurotransmitter signaling, and promotes neuroinflammation, leading to learning and memory impairments. The condition also affects adult neurogenesis, particularly in the hippocampal dentate gyrus. Moreover, hypothyroidism has been linked to psychiatric disorders, including depression and anxiety, through its influence on the plasticity of the amygdala. In addition, adult-onset hypothyroidism contributes to cerebellar ataxia and peripheral neuropathy, impacting motor coordination and sensory processing. Since we come to know that adult-onset hypothyroidism in part causes irreversible changes in brain structure, prompt treatment is crucial. Furthermore, in addition to thyroid field, recent studies suggest a potential of thyroid hormone treatment beyond the thyroid disorders, such as neurodegenerative and cognitive/psychiatric disorders. This review highlights the critical role of THs in maintaining neural function and explores their therapeutic potential in addressing neurological and psychiatric conditions.