MRI features of pancreatitis, panniculitis, polyarthritis and the fourth p: The "polka dot sign." A case series and imaging review.

Pancreatitis, Panniculitis and Polyarthritis (PPP) syndrome is a poorly understood systemic illness that will initially present with pancreatitis followed by debilitating arthralgia and cutaneous manifestations. We present the largest descriptive case series known to date of 3 patients with 5 MRI's diagnosed with PPP syndrome. In each case, a detailed review of the Magnetic Resonance Imaging (MRI) features of PPP syndrome are discussed with the introduction of a descriptive "polka dot sign." Of the 5 joints evaluated, we found the predominant extra-pancreatic imaging features in PPP syndrome to be the extra-articular manifestations including panniculitis, bone marrow edema, enhancing osteitis and the "polka dot sign." Mild to moderate inflammatory changes with joint effusion, synovitis and tenosynovitis may be present, although they will typically be a lesser feature. While the term "polyarthritis" still applies, we have found the name to be somewhat misleading as typical imaging features of inflammatory arthritis are not the predominant findings. On skin biopsy, the presence of "ghost cells" are diagnostic of this rare illness. Medical professionals should feel comfortable with the characteristic imaging manifestations of PPP syndrome in the context of pancreatitis.