Neural response to transcranial magnetic stimulation in adult hypothyroidism and effect of replacement treatment.
OBJECTIVE
Despite clinical evidences that hypothyroidism is often associated with cognitive dysfunction, affective disorders and psychosis, the effects of thyroid hormone deficiency on the adult brain have been largely unexplored. We investigated the hypothesis that hypothyroidism might affect cortical excitability and modulates inhibitory and excitatory cortical circuits by using Transcranial Magnetic Stimulation.


METHODS
Cortical excitability was probed in 10 patients with overt hypothyroidism and 10 age-matched healthy controls. We tested motor thresholds and corticospinal excitability, cortical silent period and peripheral silent period, short interval intracortical inhibition, intracortical facilitation. Patients were evaluated at the time of diagnosis, as well as after 3 and 6 months replacement therapy with l-thyroxin.


RESULTS
At baseline, patients showed decreased cortical excitability, with increased resting and active motor threshold and decreased steepness of the motor evoked potential recruitment curves. These changes were paralleled by longer cortical silent period and decreased short interval intracortical inhibition. After 3 months replacement therapy, all the parameters but short interval intracortical inhibition were restored to normal values. Short interval intracortical inhibition returned to normal values only after 6 months of replacement therapy.


CONCLUSIONS
Thyroid hormones are needed to modulate cortical excitability and cortical inhibitory circuits in adults.
Rizzo
Vincenzo
V
Department of Physiology and Pharmacology, CUNY School of Medicine, New York, NY 10031, USA.
Crupi
Domenica
D
Bagnato
Sergio
S
Quartarone
Angelo
A
Benvenga
Salvatore
S
Bartolone
Luigi
L
Ghilardi
M Felice
MF
Trimarchi
Francesco
F
Girlanda
Paolo
P
Battaglia
Fortunato
F
D002540:Cerebral Cortex / Q000503:physiopathology; D003627:Data Interpretation, Statistical; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy / Q000503:physiopathology* / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D011999:Recruitment, Neurophysiological; D013963:Thyroid Hormones / Q000097:blood / Q000627:therapeutic use; D013972:Thyrotropin / Q000097:blood / Q000627:therapeutic use; D050781:Transcranial Magnetic Stimulation
D013963:Thyroid Hormones; D013972:Thyrotropin