EQUINE VETERINARY EDUCATION Equine vet. Educ. (2019) 31 (8) 413-418 doi: 10.1111/eve.12821
Case Report
PCR for antigen receptor rearrangement (PARR) clonality testing in a horse with a solitary retropharyngeal lymphoma
E. M. Collar†* , J. E. Parker†, E. M. Gorman‡, D. S. Russell‡ and B. A. Valentine‡ †Department of Clinical Sciences, Oregon State University College of Veterinary Medicine; and ‡Department of Biomedical Sciences, Oregon State University College of Veterinary Medicine, Corvallis, Oregon, USA. *Corresponding author email:
elizabeth.collar@
oregonstate.edu
Keywords: horse; lymphoma; PCR for antigen receptor rearrangement; antigen receptor rearrangement; clonality
Summary A 19-year-old Quarter Horse gelding was evaluated for respiratory distress and a rapidly enlarging retropharyngeal mass. Initial evaluation revealed severe respiratory distress, and a large, firm mass, visibly appreciable as 12 3 12 cm, in the left retropharyngeal and perilaryngeal region, with surrounding left and right retropharyngeal swelling. No significant abnormalities were present on complete blood count and serum biochemistry analyses. Endoscopy revealed severe pharyngeal collapse restricting airflow without gross abnormalities of the pharyngeal mucosa other than inflammation and irritation. A multilobular retropharyngeal mass, diffusely heterogeneous in echogenicity, was present adjacent to, but not occluding, the carotid artery as assessed by ultrasonography. Initial needle aspirate suggested lymphoma. Tissue biopsy and histopathology confirmed a round cell tumour. A temporary tracheotomy was performed to provide respiratory relief, and the horse was managed on oral antibiotics and anti-inflammatory medications while awaiting histopathological results. The decision was made to humanely euthanise the horse after biopsy results indicated lymphoma. Definitive diagnosis of T cell rich, large B cell lymphoma was made by combination of cytology, immunohistochemistry and molecular clonality PCR (PARR) testing. Lymphoma should be considered in horses with focal masses of the retropharyngeal region. Although treatment was not pursued, PARR testing was successful in this case and may be helpful for accurate characterisation of lymphoma in horses to more precisely determine prognosis and the most effective treatment plans, as it has been in human patients and small animals.
Introduction
Lymphoma is one of the most common malignant neoplasms of the horse, and the most common neoplasm to affect the haemolymphatic systemof the horse (Sellon 2004; Aleman 2009; Munoz et al. 2009). Lymphoma can present in nearly any location, cause varying and often nonspecific signs including enlarged lymph nodes, weight loss, ventral and limb oedema, lethargy and fever (Savage 1998; Meyer et al. 2006; Munoz et al. 2009; Taintor and Schleis 2011; Durham et al. 2013), and occur in horses with a wide range of ages (2 months to 30 years). Clinicopathological findings are usually nonspecific andmay include anaemia, neutrophilia, hyperfibrinogenaemia, hyperglobulinaemia, hypoalbuminaemia and hypercalcaemia (Savage 1998; Meyer et al. 2006; Munoz et al. 2009; Taintor and Schleis 2011). Lymphoma can present diagnostic challenges in animals, particularly in cases with inaccessible masses or cases without
a discrete mass (Burba et al. 1991; Saulez et al. 2004; Meyer et al. 2006; Marques et al. 2012; Gress et al. 2016). The inability to distinguish between populations of lymphocyctic cells has frequently led to nebulous diagnoses that waver between neoplastic or reactive in nature (Meyer et al. 2006), and PCR-based clonality testing has been helpful in other species (Gress et al. 2016). Recently, clonality has been assessed using molecular techniques in horses with leukaemia and concurrent lymphadenopathy (Badial et al. 2015). The current report represents one of only few reported cases of a solitary lymphoid tumour in a well-fleshed horse with no evidence of multicentric disease, and the first documented use of polymerase chain reaction for analysis of antigen receptor rearrangement (PARR) in equine solitary extranodal lymphoma.
Case history
A 590-kg (1298 lb) 19-year-old Quarter Horse gelding in good body condition (6/9 body condition score) was referred for evaluation of a rapidly enlarging retropharyngeal mass causing respiratory distress. Ten months prior, the gelding had begun making a loud respiratory noise when exercising that the owners described as a roaring sound. No external swelling was visible. Gradually, the gelding developed mild exercise intolerance and reportedly coughed on occasion, but continued to eat and swallow without issue. One-week prior to referral, the gelding was examined by the referring veterinarian for a left sided retropharyngeal swelling. Blood was obtained on a fine needle aspirate, and endoscopy demonstrated left pharyngeal compression. The horse remained stable until, when attempting to load the horse for transport the morning of referral, the gelding became distressed. The referring veterinarian was called to the farm and noted that the mass/swelling had significantly enlarged. He administered 40 mg of dexamethasone i.m. and monitored the horse until he was stable and could be transported for referral.
Diagnostic investigations and case management
Clinical examination and clinical pathology The horse presented in severe respiratory distress, which included signs of increased respiratory effort, tachypnoea, nostril flaring and anxious behaviour. Loud respiratory noises were audible on inhalation and exhalation. A large, discrete, approximately 12 9 12 cm retropharyngeal mass (Fig 1) was visible on the left side, just caudal to the ramus of the
© 2017 EVJ Ltd
413
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88
