Hypothyroidism in patients with pseudohypoparathyroidism type Ia: clinical evidence of resistance to TSH and TRH.
OBJECTIVE
Hypothyroidism is a manifestation of multi-hormonal resistance in pseudohypoparathyroidism type Ia (PHP Ia). The objective of the study was to determine the mechanisms of hypothyroidism in PHP Ia.


METHODS
A prospective study.


METHODS
Ten patients with PHP Ia.


METHODS
The serum concentrations of TSH, free triiodothyronine (FT(3)), free thyroxine (FT(4)), and prolactin (PRL) were measured at baseline and after stimulation with TRH (200 microg i.v).


RESULTS
The median basal serum TSH concentration was 4.92 mU/l. Basal serum TSH concentration was slightly elevated in eight patients (4.22-7.0 mU/l; normal range, 0.4-3.6 mU/l), normal in one patient (2.5 mU/l), and high in one patient (13.1 mU/l). After the TRH test, TSH concentrations increased to 13.4-36.0 mU/l (normal range, 4.0-20.0 mU/l). The absolute values after the test were normal in three patients and high in seven patients. However, TSH responses relative to the baseline value (stimulated/basal TSH and expressed as a fold increase), which reflect the relative increases after TRH stimulation, were low in seven patients (2.3- to 4.3-fold TSH) and normal in three patients. Basal FT(4) concentration was normal in seven patients and low in three patients (range, 8.4-20.0 pmol/l; mean, 14.1+/-4.3 pmol/l; normal range, 10.5-23.0 pmol/l). Basal FT(3) concentration was normal in nine patients and low in one patient (range, 0.9-5.0 pmol/l; mean, 3.8+/-1.1 pmol/l; normal range, 3.3-6.1 pmol/l). FT(4) and FT(3) were not significantly increased after the TRH test. PRL concentration was normal at baseline and increased from 7 to 96 ng/ml after TRH.


CONCLUSIONS
Our results support the hypothesis that patients with PHP Ia have impaired sensitivity to both TSH and TRH.
Balavoine
Anne-Sophie
AS
Clinique Endocrinologique Marc Linquette, CHU, 59037 Lille-Cedex, France. asbalavoine@yahoo.fr
Ladsous
Miriam
M
Velayoudom
Fritz-Line
FL
Vlaeminck
Virginie
V
Cardot-Bauters
Catherine
C
d'Herbomez
Michèle
M
Wemeau
Jean-Louis
JL
D000328:Adult; D002864:Chromogranins; D004912:Erythrocytes / Q000378:metabolism; D005260:Female; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D006801:Humans; D007037:Hypothyroidism / Q000150:complications* / Q000378:metabolism*; D008297:Male; D011388:Prolactin / Q000097:blood; D011446:Prospective Studies; D011547:Pseudohypoparathyroidism / Q000150:complications* / Q000378:metabolism*; D013972:Thyrotropin / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D002864:Chromogranins; D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D013972:Thyrotropin; C406732:GNAS protein, human; D019205:GTP-Binding Protein alpha Subunits, Gs; D013974:Thyroxine