Abstract

Polyarteritis nodosa (PAN) is a medium and small-vessel vasculitis that presents as dermal and subcutaneous nodules and retiform purpuric patches but can be difficult to diagnose due to the segmental pattern of inflammation. We present an 82-year-old woman with PAN diagnosed after a prolonged course of systemic symptoms. One year prior to presentation, she developed elbow and knee arthralgias, which progressively worsened and eventually involved the ankles and wrists. She reported recurrent, painful “knots” on her forearms. She was seen by internal medicine, rheumatology, podiatry, and orthopedic surgery without definitive diagnosis. Her work up prior to seeing dermatology was notable for an elevated CRP, rheumatoid factor, and an IgG kappa monoclonal gammopathy. Workup for inflammatory arthritis was negative. MRI without contrast of the right foot and ankle was notable for diffuse subcutaneous edema and degenerative changes. She was prescribed a two-week course of prednisone without improvement. When seen in dermatology, punch biopsies were performed on the subcutaneous nodules and retiform purpura and demonstrated brisk inflammation of medium vessels in the subcutis with minimal associated panniculitis consistent with PAN. Histopathologically, PAN demonstrates leukocytoclastic vasculitis of the superficial dermal vessels with necrotizing vasculitis of the muscular arteries of the deep dermis or subcutaneous fat. As the features can be focal and segmental, diagnosis may require more than one biopsy and highest diagnostic yield may be found in the subcutaneous nodule as demonstrated in this case. This case highlights the importance of multi-disciplinary teams and appropriate skin biopsy in the diagnosis of PAN.