Case history
A 42-year-old Japanese woman presented with a 4-week history of myalgia. Two weeks before her visit to our hospital, her pain began to spread from the neck to the chest, resulting in extreme myalgia four days prior to her visit. The pain was sudden, non-persistent, and generalised with no clear localisation. There was no change in her symptoms owing to diet. The patient reported excessive sweating and weight loss (5 kg/6 months); however, tremors, diarrhoea, and diplopia were absent. She had no remarkable family history, though her medical history included pyelonephritis. Furthermore, she was not taking any oral medications or supplements.
On examination, the patient appeared ill and was afebrile (37.0 °C). Her blood pressure was 110/64 mmHg, pulse 90/min, respiratory rate 16/min with an O2 saturation of 98% on room air. Physical examination revealed no ocular protrusion or eye movement disorder. Her thyroid gland was diffusely enlarged, but there was no associated tenderness or nodule present. Her cardiac examination results were normal, and lungs were clear on auscultation. There were no abnormal abdominal findings. Findings of neurological examinations, including tests for muscle weakness, muscle grasping pain, muscle atrophy, and deep tendon reflexes, were completely unremarkable.
On admission, initial investigations revealed mild anaemia. Inflammatory markers and kidney function test results were normal, but liver function test values were mildly elevated. Creatinine kinase, serum calcium, and serum phosphate levels were normal. Further examination revealed free triiodothyronine (FT3) > 30.00 ng/mL, free thyroxine (FT4) 3.45 ng/mL, TSH < 0.01 µIU/mL, and findings of thyrotoxicosis. Additionally, she tested positive for TRAb (6.4 IU/L). The results of tests for autoantibodies, including antinuclear antibodies, were negative (Table 1).
Cervical ultrasonography showed diffuse enlargement of the thyroid gland and increased blood flow with a colour Doppler scan of 57.6 cm/s and 48.1 cm/s on the right and left, respectively. Consequently, she was diagnosed with Basedow’s disease. Since there were no specific symptoms and autoantibodies were absent, we concluded that there was no complication of myositis. Treatment with mercazole 15 mg and potassium iodide 50 mg was initiated, leading to an improvement in FT3 (> 4.49 ng/mL) and FT4 (1.31 ng/mL) levels after one month of treatment. Myalgia disappeared one week after the administration of the anti-thyroid medication. Thereafter, the condition of the patient improved without any relapse of pain.