Evidence for a specific defect in hippocampal memory in overt and subclinical hypothyroidism.
BACKGROUND
Declarative memory largely depends upon normal functioning temporal lobes (hippocampal complex) and prefrontal cortex. Animal studies suggest abnormal hippocampal function in hypothyroidism.


OBJECTIVE
The aim of the study was to assess declarative memory in overt and subclinical (SCH) hypothyroid patients before and after l-T(4) (LT4) replacement and in matched normal subjects.


METHODS
A prospective, open-labeled interventional study was conducted at a teaching hospital.


METHODS
Hypothyroid (n = 21) and SCH (n = 17) patients underwent neuropsychological tests at baseline and 3 and 6 months after LT4 replacement. Normal subjects were studied at the same time-points.


RESULTS
Tests of spatial, verbal, associative, and working memory; attention; and response inhibition and the Hospital Anxiety and Depression Scale were administered.


RESULTS
Baseline deficits in spatial, associative, and verbal memory, which rely upon the integrity of the hippocampal and frontal areas, were identified in patients with overt hypothyroidism. Spatial and verbal memory were impaired in SCH patients (P < 0.05). TSH levels correlated negatively (P < 0.05) with these deficits. After LT4 replacement, verbal memory normalized. Spatial memory normalized in the SCH group but remained impaired in the hypothyroid group. Associative memory deficits persisted in the overt hypothyroid group. Hospital Anxiety and Depression Scale scores did not correlate with cognitive function. Measures of attention and response inhibition did not differ from control subjects.


CONCLUSIONS
Cognitive impairment occurs in SCH and more markedly in overt hypothyroidism. These impairments appear predominantly mnemonic in nature, suggesting that the etiology is not indicative of general cognitive slowing. We propose that these deficits may reflect an underlying disruption of normal hippocampal function and/or connectivity.
Correia
Neuman
N
Department of Endocrinology and Diabetes, Adelaide and Meath Hospital, incorporating the National Children's Hospital, Tallaght, Dublin 24, Ireland.
Mullally
Sinead
S
Cooke
Gillian
G
Tun
Tommy Kyaw
TK
Phelan
Niamh
N
Feeney
Joanne
J
Fitzgibbon
Maria
M
Boran
Gerard
G
O'Mara
Shane
S
Gibney
James
J
D000328:Adult; D000368:Aged; D001288:Attention; D016022:Case-Control Studies; D005260:Female; D006624:Hippocampus / Q000503:physiopathology*; D006784:Hospitals, Teaching; D006801:Humans; D007037:Hypothyroidism / Q000150:complications* / Q000188:drug therapy / Q000503:physiopathology* / Q000523:psychology; D008297:Male; D008568:Memory; D008569:Memory Disorders / Q000209:etiology* / Q000503:physiopathology* / Q000523:psychology; D008570:Memory, Short-Term; D011939:Mental Recall; D008875:Middle Aged; D009483:Neuropsychological Tests; D013974:Thyroxine / Q000627:therapeutic use*
D013974:Thyroxine