Congential hypothyroidism and the hippocampus

A lack of thyroid hormone among children with congenital hypothyroidism appears to cause deficiencies in the hippocampus that impairs learning and memory retrieval, researchers reported here at the 15th International Thyroid Congress (ITC).

The observations might offer insight into memory deficits seen in children with congenital hypothyroidism (CH) even when they’re screened property and get optimal care, according to Joanne Rovet, PhD, The Hospital for Sick Children, Toronto, Ontario.

Even children receiving proper care have been found to have mild reductions in IQ and subtle neurocognitive deficits that persist. Parents report that even as children get older, they forget where they put things, forget recent events, and forget what they were told.

Using functional magnetic resonance imaging (MRI), researchers tested activity in the hippocampus of children with CH while they identified objects in a “new” location versus an “old” one.

Both groups showed more hippocampus activation when identifying “new” objects. However, they found that the effect was stronger in the left middle hippocampus in the subject children than in the control children. This suggests that children with CH have to activate the hippocampus more than normal to make visual associations.

In their latest findings, they tested the activity of the hippocampus in 14 patients with CH versus 14 control subjects in a verbal memory test. The average age in both groups was 13 years.

All the children were shown 2 words and asked to form a sentence using the words to help them remember the words. Later, they were shown pairs of words. Some of the pairs included 2 words they had seen before, some with just one word -- or “item” -- they’d seen before, and others that included no words they’d seen before. The children were asked to identify the words they had previously seen.
The children with CH were less accurate in their recall, with later age at treatment onset significantly associated with poor recognition of pairs (P = .02) and with overall accuracy (P = .03).

And interestingly, among the CH children, there were no regions of the hippocampus that were significantly different for pair recognition versus single item recognition. However, in the control children, the right anterior hippocampus showed a significantly larger distinction between pairs and single items, compared with the children with CH (P = .002).

The functional MRI findings show that there is “de-engagement” in children with CH during item processing, meaning less specialisation in memory formation in these tasks. They also show “reduced engagement” during the processing of relations of words, suggesting less adequate processing in the left middle hippocampus.

Because the researchers found no effects of TSH levels at the time diagnosis, it seems that the effects were unrelated to their initial hypothyroidism level.

“This may explain why children with congenital hypothyroidism still experience memory deficits despite newborn screening and optimal care,” said Dr. Rovet.

Presentation title: Atypical Hippocampal Functioning During Verbal Memory Recall in Youth With Congenital Hypothyroidism. Abstract 8

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