MRCP2-4051

MRCP2-4051

A 55-year-old man presents with a history of feeling generally unwell for several months. He reports experiencing fever, malaise, and weight loss. He has also been experiencing muscle aches and pain in several joints, although none have swollen. Recently, he has developed a cough that produces fresh blood and has become short of breath.

Upon conducting blood tests, the following results were obtained:
– Haemoglobin: 99 g/L (130 – 180)
– White cell count: 9.1 ×109/L (4 – 11)
– Platelets: 134 ×109/L (150 – 400)
– Sodium: 136 mmol/L (137 – 144)
– Potassium: 3.9 mmol/L (3.5 – 4.9)
– Urea: 28.9 mmol/L (2.5 – 7.5)
– Creatinine: 412 μmol/L (60 – 110)

A urine dipstick also revealed 2+ protein and 3+ blood. Autoantibodies were sent and the anti-neutrophil cytoplasmic antibody was positive with perinuclear staining. Further testing revealed a raised MPO (myeloperoxidase) titre at 73 U/ml (<6). What is the most likely underlying diagnosis for this 55-year-old man?