EQUINE VETERINARY EDUCATION / AE / MARCH 2015


119


Case Report


Multiple skeletal metastases from a penile squamous cell carcinoma in a horse


B. B. Nelson, E. F. Edmondson†, J. M. Sonis‡, C. B. Frank†, A. Valdés-Martínez§ and B. S. Leise*


Department of Clinical Sciences and †Microbiology, Immunology and Pathology, §Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado; and ‡Hagyard Equine Medical Institute, Lexington, Kentucky, USA. *Corresponding author email: britta.leise@colostate.edu


Keywords: horse; squamous cell; carcinoma; metastasis; bone


Summary A 21-year-old gelding with ventral abdominal and preputial oedema was evaluated for right hindlimb lameness. Partial phallectomy had been performed 3 years prior for treatment of squamous cell carcinoma. Regional analgesia did not localise the source of lameness and nuclear scintigraphy was recommended. The results of the scan revealed severe increased radiopharmaceutical uptake in the proximal femur. Radiographic and ultrasound examinations were inconclusive. The horse was discharged with recommendations of stall confinement and a 2 week course of nonsteroidal anti-inflammatory drugs. Four weeks later the horse presented for an inability to elevate his neck and persistent hindlimb lameness. The owner elected humane euthanasia. Post mortem examination revealed metastatic squamous cell carcinoma in the proximal femur and fifth cervical vertebrae consistent with metastasis from the penile squamous cell carcinoma. To the authors’ knowledge, multiple site bone metastasis of squamous cell carcinoma has not been reported previously in the horse.


Introduction


The penis and preputial region is the second most common location for tumours in the horse, second only to skin and the subcutaneous tissues (Brinsko 1998). Squamous cell carcinoma (SCC) is the most common genital tumour in the horse and most commonly affects older males (Howarth et al. 1991; Mair et al. 2000). Regional metastasis to local lymph nodes is not uncommon. A large case series demonstrated that 7 out of 82 (8.5%) horses with penile SCC had regional lymph node metastasis (van den Top et al. 2008). While regional lymph node involvement can occur with SCC, distant metastasis is extremely rare. In humans, penile SCC is reported to metastasise via lymphatic drainage to inguinal lymph nodes followed by pelvic lymph nodes prior to a distant metastasis (Zhu et al. 2011). The most common sites of distant metastasis following SCC in the horse include the lungs, heart and liver (Cramer et al. 2011) and a single report documented metastasis to bone (Patterson et al. 1990). The local invasiveness of SCC into adjacent bone (osteolysis) has also been described (Dixon and Head 1999). This report describes the case of a horse with multiple SCC skeletal metastases suspected from penile origin.


Case history


A 21-year old Thoroughbred gelding presented to the Veterinary Teaching Hospital at Colorado State University for a history of right hindlimb lameness and ventral abdominal and preputial oedema. Three years prior to presentation, the horse had a partial phallectomy for SCC, which was confirmed by histopathology. One month prior to hospital presentation, the horse developed ventral pitting oedema that included the preputial sheath and a right hindlimb lameness was observed and persisted until hospital presentation. A complete blood count and biochemistry profile were performed by the referring veterinarian, which did not reveal any abnormalities aside from a mild thrombocytopenia (76 × 109/l; reference range: 100–600 × 109/l). Lameness examination by the referring veterinarian revealed a grade 3/5 lameness of the right hindlimb. An abaxial nerve block did not improve the lameness. A peroneal-tibial nerve block improved the baseline lameness 20%, and intra-articular stifle anaesthesia did not change the lameness. Transabdominal ultrasound and rectal palpation did not reveal any abnormalities. Examination of his penis revealed small raised areas present near the site of prior amputation, which were histologically consistent with scar tissue. The horse was placed on a course of phenylbutazone and referred for further evaluation of his persistent lameness.


Clinical findings


Upon presentation the horse was quiet and alert with its temperature, pulse and respiratory rates within normal reference intervals. The horse was in mildly decreased body condition (2 out of 5) and weighed 454 kg. Cardiac and pulmonary auscultation did not reveal any murmurs or respiratory abnormalities. Gastrointestinal borborygmi were present in all quadrants. His hydration status was estimated to be normal and digital pulses palpated normally on all 4 feet. A plaque of oedema was present on the abdomen from ventral midline extending to his preputial sheath. The oedema was cold, pitting and nonpainful. Orthopaedic examination did not reveal any palpable swellings or pain elicited in his neck, forelimbs or spine. The horse was reluctant to flex the right hindlimb, and palpation and manipulation of the pelvic region elicited pain. Lameness examination revealed a grade 3.5/5 lameness in


the right hindlimb on a hard flat surface (American Association of Equine Practitioners 1991). Hoof testers were applied and


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