MRCP2-1120

MRCP2-1120

A 28-year-old woman, who has a 9-month-old baby, presents with neck and throat pain over the area of her thyroid. She tells you that she had a flu-like illness a week or so before the pain began. Her partner, who also attends the appointment, tells you she has been nervous and agitated over the past week. On examination, there is a mild diffuse enlargement of the thyroid gland and it is tender to palpation. Her BP is 141/82 mmHg, and her pulse is 85/min and regular at rest. She has a slight tremor.

Investigations reveal the following:
Haemoglobin (Hb) 121 g/l (normal values: 115–155 g/l)
White cell count (WCC) 6.1 × 109/l (normal values: 4.0–11.0 × 109/l)
Platelets (PLT) 170 × 109/l (normal values: 150–400 × 109/l)
Sodium (Na+) 139 mmol/l (normal values: 135–145 mmol/l)
Potassium (K+) 4.6 mmol/l (normal values: 3.5–5.0 mmol/l)
Creatinine (Cr) 100 μmol/l (normal values: 50–120 μmol/l)
Thyroid-stimulating hormone (TSH) <0.05 U/l
Anti-TPO Negative
Erythrocyte sedimentation rate (ESR) 62 mm/hour (normal values: 1–20 mm/hour)
fT4 24.3 pmol/l
Radioiodine uptake on the isotope scan is decreased.

Which of the following forms of thyroiditis is the most likely diagnosis?