Metastatic paraganglioma presenting as a primary shoulder mass

Paragangliomas uncommonly metastasize, including to the bones, wherein these tumors are designated as malignant paragangliomas. A 56-year-old man presented with pain and immobility in his right arm for 1 year. He had a history of controlled hypertension and diabetes mellitus for 2 years. He had also been taking anti-anxiety medications for 25 years. His shoulder imaging revealed an expansile, lytic, destructive lesion in the glenoid cavity, measuring 4.6 × 3.9 × 3.2 cm, involving the adjacent bones and soft tissues. A whole-body PET-CT scan revealed a hypermetabolic destructive mass in the right glenoid cavity and another lesion in his abdomen in the aortocaval region. Initial biopsy and subsequent scapular resection microscopically revealed a multinodular tumor with polygonal cells arranged in a nesting and diffuse pattern, in a vascularized and sclerotic stroma. Tumor cells displayed moderate to abundant, eosinophilic to clear cytoplasm, fine nuclear chromatin, focal intranuclear inclusions, and scattered mitotic figures. Immunohistochemically, tumor cells were positive for vimentin, synaptophysin, chromogranin, and CD56 and negative for AE1/AE3, CK, EMA, CD10, SMA, Melan A, HMB-45, desmin, and S100-P. Biopsy of the abdominal mass revealed foci of tumor cells resembling the scapular tumor. Diagnosis of a malignant paraganglioma was finally offered. The patient's post-operative blood pressure is controlled. Currently, his urinary vanillylmandelic acid and metanephrine levels are normal. He is asymptomatic 11 months post-surgery and is on follow-up. This unusual case is presented to increase a diagnostic index of suspicion for a malignant paraganglioma, including at unconventional musculoskeletal sites. The diagnostic challenge and therapeutic implications are discussed herewith.