MSFinals-5904

A 76-year-old woman, who was previously in good health, presents for review. For the past 2–3 months, she has suffered from increasing pain and stiffness, particularly in the early part of the day, affecting her shoulders and, most recently, her hips. There has also been low-grade fever and she has lost 4 kg in weight. Examination reveals normal proximal muscle strength.
Investigations:
Investigation Result Normal value
Haemoglobin 111 g/l 115–155 g/l
Mean corpuscular volume (MCV) 96 fl 76–98 fl
White cell count (WCC) 6.1 × 109/l 4–11 × 109/l
Platelets 345 × 109/l 150–400 × 109/l
Erythrocyte sedimentation rate (ESR) 75 mm/h 0–10mm in the 1st hour
Sodium (Na+) 140 mmol/l 135–145 mmol/l
Potassium (K+) 5.0 mmol/l 3.5–5.0 mmol/l
Creatinine 130 μmol/l 50–120 µmol/l
Creatine kinase 31 IU/l 23–175 IU/l
Alanine aminotransferase (ALT) 45 IU/l 5–30 IU/l
Chest X-ray (CXR) Slight cardiomegaly, otherwise normal
Which of the following is the most likely diagnosis?