26th May 2025

A 32-year-old male presents with a 3-month history of back pain and stiffness, which he describes as being worse first thing in the morning, but gradually improves throughout the day.

A 32-year-old male presents with a 3-month history of back pain and stiffness, which he describes as being worse first thing in the morning, but gradually improves throughout the day. He is otherwise fit and well and works as a builder. He denies any history of trauma or the presence of any weight loss or night sweats. His father had a skin condition which he cannot remember the name of. On examination, he has reduced spinal flexion and sacroiliac joint tenderness. Blood test results showed the following.

Hb 140 g/L (130-180)

MCV 90fL (80-96)

WCC 5.0 x 10⁹/L (4.0-11.0)

CRP 26 mg/L (<10)

Sodium 138 (133–146 mmol/L)

Potassium 3.9 (3.5–5.3 mmol/L)

Creatinine 60 (45–84 μmol/ L)

EGFR >90 

ESR 5

LFTs normal 

Rheumatoid factor 8 (0-20 u/mL)

Anti-CCP negative 

An x-ray of his spine revealed right-sided sacroiliitis and presence of scattered syndesmophytes on the same side. 

What is the most likely diagnosis? 

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