19th January 2024

A 32-year-old male presents to ED with a one-week history of back pain and stiffness, which he describes as being worse first thing in the morning.

A 32-year-old male presents to ED with a one-week history of back pain and stiffness, which he describes as being worse first thing in the morning. He has also noticed pain and redness in his right eye for the past day and a rash on the soles of his feet. He is normally fit and well and has no past medical history. However, he recalls having a ‘stomach bug’ around 3 weeks ago. Blood test results showed the following.

Hb 140 g/L (130-180)

MCV 92fL (80-96)

WCC 5.0 x 10⁹/L (4.0-11.0)

CRP 96 mg/L (<10)

Sodium 138 (133–146 mmol/L)

Potassium 4.9 (3.5–5.3 mmol/L)

Creatinine 68 (45–84 μmol/ L)

EGFR >90

ESR 3

LFTs normal

Rheumatoid factor 8 (0-20 u/mL)

What is the most likely diagnosis?