Widespread lytic lesions—A metastatic or vasculitic process?

INTRODUCTION: This case highlights the complexities in the initial diagnosis and investigations of widespread lytic lesions initially perceived to be a widespread metastatic process and the consideration of alternative diagnosis. PRESENTATION OF CASE: A 57 year-old man with a background of psoriatic arthritis presented to the rheumatology department with lumbar back pain and sensory disturbance over L4/5. Magnetic resonance imaging (MRI) and bone scan identified lesions consistent with bony metastases at L5. The patient previously had a raised prostate specific antigen (PSA) of 10.8 μg/L (normal < 4) but prostate biopsy was benign. Multiple metastatic deposits in the liver and kidneys (confirmed necrotic tissue on biopsy) were identified through further investigations. The initial diagnosis of malignancy was challenged after a positron emission tomography (PET) scan showed lesions highly suggestive of polyarteritis nodosa (PAN) and subsequent magnetic resonance angiogram (MRA) revealed stenosis and aneurysm in the renal artery in keeping with PAN. Therefore what was initially thought to be a widespread metastatic disease process was in fact the manifestation of a systemic vasculitic disease. DISCUSSION: PAN is a vasculitis that predominantly involves small to medium-sized vessels. The disease can affect any site in the body, but holds a predisposition for organs such as kidneys, heart and the gastrointestinal tract. Differential diagnosis of PAN should be considered in patients with widespread lytic lesions. CONCLUSION: Due to the pathological nature of PAN and its variable clinical manifestations that add to the challenges of its diagnosis, one must hold a high clinical suspicion, even in urological conditions.