Case presentation:
A 34-year-old woman with no medical history presented to our department with a five-day history of arthritis affecting the small joints of the left hand, wrist, right elbow, and ankle. She had myalgia without sicca symptoms.
Physical examination showed a normal blood pressure of 110/60 mmHg, synovitis of the left wrist and metacarpophalangeal joints, right elbow, and ankle.
Laboratory findings revealed a high C-reactive protein level (28 mg/L, Normal value (N) < 6), normocytic anemia (hemoglobin: 7.7 g/dL, N ≥ 12 g/dL, mean corpuscular volume: 96.5 femtoliter, N: 80 – 100), high Lactate dehydrogenase (LDH) level (280 IU/L, N: 91 – 260), and high Creatine-phosphokinase (CPK) level (485 IU/L, N: 22 – 269). Liver and renal tests were within the normal range.
Anti-nuclear antibodies (ANA), anti-SSA, SSB, rheumatoid factor, and anti-citrullinated protein antibodies (ACPA) were negative.
C3 and C4 complement levels were normal. Thyroxine (T4) level was low (2.8 pmol/L, N: 7.9 – 14.4), and thyroid-stimulating hormone (TSH) level was high (39 µIU/L, N: 0.34 – 5.6). The thyroid peroxidase antibodies were positive (670 IU/mL, N: <35 IU/mL), whereas anti-thyroglobulin antibodies were negative.
Radiographs of hands, feet, and pelvic were without abnormalities. Musculoskeletal ultrasound showed synovial thickening of the left wrist and the right elbow with hyperemia in power Doppler imaging. There was also synovial thickening of the left metacarpophalangeal joints, right ankle, and tenosynovitis of the posterior tibial  and fibular tendons. The chest radiograph was normal. Thyroid ultrasound showed inhomogeneous and hypoechogenic thyroid parenchyma. However, ultrasonography of the salivary glands was without abnormalities.
The diagnosis of primary hypothyroidism related to Hashimoto thyroiditis was made. There were not enough criteria to make the diagnosis of Sjogren’s syndrome.
A thyroid hormone replacement therapy was started at 25µg daily and increased progressively to reach 150 µg daily.
After three months of treatment, the TSH level had become within the normal range, and polyarthritis had disappeared. The TSH level remained stable, and the patient didn’t develop a recurrence of the polyarthritis after 20 months of follow-up.
Consent from the patient for publication of this case study was obtained.