9th June 2025

A 65-year-old man presents with a year’s history of headache, abdominal pain, diarrhoea, pruritus and flushing.

A 65-year-old man presents with a year’s history of headache, abdominal pain, diarrhoea, pruritus and flushing. He has been more tired than usual and reports a widespread itchy red rash which becomes a wheal when scratched.

On examination his chest is clear, heart sounds are normal and he has non-tender hepatosplenomegaly. He has red-brown papules across his trunk, arms and legs. 

Investigations are as follows:

Hb 123 g/L Male: (135-180)

Platelets 190 * 109/L (150 – 400)

WBC 12.0 * 109/L (4.0 – 11.0)

Na+ 142 mmol/L (135 – 145)

K+ 4.3 mmol/L (3.5 – 5.0)

Urea 6.8 mmol/L (2.0 – 7.0)

Creatinine 75 µmol/L (55 – 120)

CRP  <5 mg/L   (< 5)

Which diagnosis best fits with this clinical picture?