Euthyroid sick syndrome and inhibitory effect of sera on the activity of thyroid 5'-deiodinase in systemic sclerosis.
OBJECTIVE
Our aim was to demonstrate the occurrence of euthyreoid sick syndrome in patients with systemic sclerosis (SSc). Furthermore, the presence of anti-thyroid antibodies and their relationship to thyroid 5'-deiodinase activity was investigated.


METHODS
The activity of thyroid 5'-deiodinase was measured by 5' outer ring-deiodination using the sera of patients with SSc (n = 21), undifferentiated connective tissue disease (n = 12), and secondary (n = 19) and primary (n = 11) Raynaud's syndrome (RP). Patients with acute cardiovascular events at the time of the study (n = 16) were investigated as controls.


RESULTS
Low FT3 (FT3 < 2.5 pg/ml) was frequently demonstrated in all the patient groups (9/21, 3/12, 10/19 and 8/11, respectively). The high frequency of a FT3/FT4 ratio < 0.2 representing euthyreoid sick syndrome was also often found in SSc (14 cases) and primary (12 cases) and secondary (6 cases) RP patients. Anti-thyroid peroxidase antibody was detected in 17 patients with SSc and in 7, 8 and 3 cases with undifferentiated connective tissue disease, secondary and primary Raynaud's phenomenon, respectively, and in none of the controls. The inhibiting effect of sera on the activity of thyroid 5'-deiodinase was higher in patients with anti-thyroid peroxidase antibodies compared to antibody negative cases (P < 0.01). An inverse correlation was shown between the levels of anti-thyroid peroxidase antibodies and the decreased activity of thyroid 5'-deiodinase (r = -0.6111, P < 0.02) in patients with low FT3.


CONCLUSIONS
The low FT3 or FT3/FT4 ratio observed supports the hypothesis that euthyroid sick syndrome is often present in SSc. Anti-thyroid antibody is also frequently detected in SSc and the positive sera inhibit the activity of thyroid 5'-deiodinase, which can contribute to the low FT3 or FT3/FT4 ratio. Anti-thyroid peroxidase antibodies may play an additive role in the development of low FT3 levels via the inhibiting effect of thyroid 5'-deiodinase. The low FT3 levels may directly influence the already impaired microcirculation in SSc by increasing the systemic vascular resistance.
Molnár
I
I
3rd Department of Internal Medicine, Kenézy County and Teaching Hospital, Debrecen, Hungary.
Czirják
L
L
D000208:Acute Disease; D000328:Adult; D000906:Antibodies / Q000032:analysis; D001790:Blood Physiological Phenomena; D002318:Cardiovascular Diseases / Q000097:blood / Q000150:complications / Q000201:enzymology; D003240:Connective Tissue Diseases / Q000097:blood / Q000150:complications / Q000201:enzymology; D005067:Euthyroid Sick Syndromes / Q000209:etiology*; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000037:antagonists & inhibitors* / Q000276:immunology / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D011928:Raynaud Disease / Q000097:blood / Q000201:enzymology / Q000209:etiology; D012594:Scleroderma, Localized / Q000097:blood / Q000150:complications* / Q000201:enzymology* / Q000276:immunology; D012595:Scleroderma, Systemic / Q000097:blood / Q000150:complications* / Q000201:enzymology* / Q000276:immunology / Q000378:metabolism; D013961:Thyroid Gland / Q000201:enzymology*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D000906:Antibodies; D014284:Triiodothyronine; D007453:Iodide Peroxidase; D013974:Thyroxine