Objective: To investigate using magnetic resonance imaging (MRI) the part played by flexor and extensor tenosynovitis and synovitis of the metatarsophalangeal (MTP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints in producing the "sausage-like" aspect of spondyloarthropathy (SpA) toe dactylitis.
Methods: Twelve sausage-like toes and corresponding contralateral toes of 7 consecutive patients meeting Amor criteria for SpA were studied by MRI.
Results: All dactylitic toes showed fluid collections in the flexor synovial sheaths on MRI. Due to the sheath distension the plantar bone to skin distance was significantly increased (p < 0.05) in the dactylitic toes compared to normal contralateral toes. Peritendinous soft tissues were not involved since these were significantly thicker (p < 0.05) in normal toes. Extensor synovial sheaths were involved in only 4 dactylitic toes. Of the 36 joints of the 12 dactylitic toes only 2 MTP joints showed capsule distension. Considering MRI as the "gold standard", examination showed 100% sensitivity and specificity for flexor sheath involvement but lacked sensitivity for extensor synovial sheaths and showed a low specificity for joint capsule distension.
Conclusion: Like finger dactylitis, toe dactylitis may also be due to flexor tenosynovitis and synovitis of MTP, PIP, and DIP joints may not be a required condition for sausage-shaped appearance. Extensor tenosynovitis may be present in addition to flexor tenosynovitis. Physical examination is a sufficient method for diagnosing toe dactylitis.