An 8 yr old, reportedly castrated male Boston terrier presented with a history of generalized hyperesthesia and intermittent shifting leg lameness. Physical examination revealed a caudal abdominal mass and bilateral shoulder pain. A complete blood count, serum biochemistry panel, and urinalysis were unremarkable. Thoracic radiographs demonstrated bony proliferation and lysis of the third sternebra, an expansile lesion of the left tenth rib, and lucency in both proximal humeral metaphyses. Abdominal radiographs and ultrasound revealed a soft tissue mass within the caudoventral right abdomen. Ultrasonography also revealed an enlarged lymph node within the right retroperitoneal space. Exploratory laparotomy identified the mass as a retained testicle. A cryptorchidectomy, lymph node biopsy, and bilateral percutaneous core biopsies of the proximal humeri were performed. Histopathologic examination revealed malignant seminoma of the testicle with metastasis to lymph node and bone. Adjuvant chemotherapy was recommended, but it was declined by the owner. All follow-up was lost. This case highlights a unique case for causative hyperesthesia secondary to a novel site of metastasis from malignant seminoma. Metastasis to bone has not been reported in humans or dogs and represents a very unusual and aberrant variant of the normally relatively benign biological behavior of seminoma in the dog.

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