According to Dr. Herbert Kaplan, MD (retired), Denver, CO, pain may be the only complaint of people with undifferentiated spondyloarthropathy. Most people with USpA have one or more of the following symptoms:

• Inflammatory back pain
  
  
• Unilateral or alternating buttock pain
  
  
• Enethesitis - inflammation where a tendon or ligament attaches to the bone
  
  
• Peripheral arthritis
  
  
• Arthritis of the small joints
  
  
• Swollen fingers or toes
  
  
• Heel pain
  
  
• Fatigue
  
  
• Iritis
  
  

Onset of the disease is often insidious and, even years of disease inflammation or calcification of the sacroiliac joints (the joints where the spine meets the pelvis) is often absent or mild on routine x-rays.

According to some experts, the age of onset is very wide and tends to peak at age 50. Unlike AS, USpA is more common in females and only 20-25% of people with USpA are HLA-B27 positive.

Some people with undifferentiated spondyloarthropathy later develop symptoms of the other forms of spondylitis, such as AS, but many will continue to have chronic, but not severe symptoms, and remain "undifferentiated."