Background/Purpose:

Thyroid dysfunction is common in rheumatoid arthritis (RA). Subclinical hypothyroidism is the first most common, followed by clinical hypothyroidism. Thyroid dysfunction in RA had been found to increase the risk of cardiovascular disease. Subclinical hypothyroidism is defined as increased serum thyroid stimulating hormone (TSH) concentration with normal serum free thyroxine (T4) level. The aim of this study was to compare the thyroid function in early RA patients (of less than one-year duration of RA symptoms) versus established RA patients (of more than or equal to one-year duration of RA symptoms).

Methods:

We recruited 35 early RA patients (ERA) and 52 established RA patients attending specialized rheumatology clinic. All the patients had no clinical evidence of thyroid dysfunction. Patients with diabetes, pregnancy, renal and liver impairment were excluded. Fasting Free thyroxine (FT4), Free triiodothyronine (FT3), and thyroid stimulating hormone (TSH) were assessed in all the participants. t-test was used to compare the RA disease characteristics and the thyroid function between early and established RA. P value of <0.05 was considered significant.

Results:

Rheumatoid arthritis patients had been recruited through a specialized rheumatology clinic, 35 were with new onset rheumatoid arthritis (early RA; ERA of less than a year of RA symptoms onset) and 52 were with established RA (of more than a year of RA symptoms onset). The mean RA duration was 7.4 ± 2.0 months for ERA and 96 ± 92 months for the established RA group. There were no significant differences in age (45.76 ± 2.45 years for ERA vs. established RA respectively, p=0.49), or in gender distribution (31 F and 4 M in ERA vs. 46 F and 6 M in established RA, p=0.9) between the two groups.

ERA compared to the established RA group had more active RA as manifested by more swollen 28- joints (5.7 vs 1.7, respectively, p=0.001), more tender 28-joints (17 vs 11, respectively, p=0.01), higher DAS-28-ESR score (5.8 vs 4.5, respectively, p.0001), higher DAS 28-CRP score (5.1 vs. 3.9, respectively, p=0.001), and longer morning stiffness duration (in minutes) (p=0.04). As well, ERA had lower HDL level (1.4 vs 1.2, respectively, p=0.04). On the other hand, established-RA patients had RA disease onset at an earlier age than the EAR group (36.5 vs 44 years, respectively, p=0.02)

While the mean TSH, T3 and T4 were within normal range in both groups, there were significant differences in the mean values between ERA and established RA. TSH was 2.12±1.52 in ERA vs. 5.8±8.3 in established RA (NR:0.27-4.2 mlU/L), p=0.04. Mean FT3 was 4.54± 0.53 in ERA vs. 3.61± 1.13 in the established RA (NR: 4-6.8 pmol/L), p=0.04. Average FT4 was 17.7 ± 4.77 in ERA vs. 15.3 ± 2.51 in the established RA (NR: 12-22 pmol/L), p=0.01.

Conclusion:

RA patients with more than a year of RA symptoms are at a higher risk of silent autoimmune thyroid disease than their age sex matched RA patients with new onset RA; of less than a year of RA symptoms onset. Regular assessment of thyroid function might be an important part in the routine biochemical and immunological profile screening of RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/thyroid-function-in-early-versus-established-rheumatoid-arthritis/