MRCP2-0907
A 56-year-old man presents to the dermatology clinic with a hyperpigmented rash on his neck, axillae, and groin that has worsened over the past few weeks. He reports increased shortness of breath and decreased exercise tolerance over the past 3 months. He is a smoker and has COPD, which is treated with a high dose salmeterol/fluticasone inhaler. On examination, he has a blood pressure of 132/82 mmHg, a pulse of 65 beats per minute, and a BMI of 22 kg/m². There is a quiet wheeze on chest auscultation and mild tenderness in the epigastrium.
Investigations reveal a hemoglobin level of 90 g/l, platelets of 191 * 109/l, WBC of 7.0 * 109/l, and elevated CRP and ESR levels. His electrolyte and renal function tests are within normal limits.
What is the most appropriate next investigation to perform?