Diagnosis and treatment of a periocular myxosarcoma in a bearded dragon (Pogona vitticeps)

Abstract

A 5-year-old male Australian bearded dragon (Pogona vitticeps) was presented with a 2-month history of a periocular mass. The clinical evaluation included a physical examination, hematology, biochemistry, and radiographs. The mass was treated surgically and diagnosed as myxosarcoma. Strontium-90 plesiotherapy was attempted, but the mass recurred 5 mo later.

Bearded dragons are presented for various diseases, including neoplasia (1). Neoplasms are commonly encountered in lizards, though they were once thought to be uncommon (2–7). Soft tissue sarcomas, of which myxosarcoma is one type, are the most common neoplasms and comprise about 11% of all reported neoplasms in lizards (2). The following describes a case of periocular myxosarcoma in a bearded dragon, in which treatment with strontium-90 (⁹⁰Sr) was attempted following surgery.

Case description

A 5-year-old male Australian bearded dragon (Pogona vitticeps) was referred to the Ontario Veterinary College Health Sciences Centre (OVC-HSC) following a 2-month history of an ocular mass in the medial canthus of the right eye. The lizard displayed epiphora and hyperemia and was non-responsive to ophthalmic antibiotic treatment (Triple antibiotic ointment — brand unknown) initiated by the referring veterinarian.

On physical examination, the lizard was bright, alert, responsive, and in good body condition (body weight of 501 g; body score of 5 out of 9). No abnormalities were noted other than the affected right eye. A 5-mm firm, pink swelling was noted at the medial canthus of the right eye, and medial to the third eyelid (Figure 1). Differential diagnoses for the swelling on the eye included neoplasia, abscess, foreign body, or bacterial causes such as mycobacteria or Chlamydophila (8).

Figure 1.

Lateral view of the bearded dragon at the initial presentation. The lizard is placed in sternal recumbency showing a firm, pink mass at the medial canthus of the eye.

A blood sample was collected from the ventral caudal (tail) vein for a complete blood (cell) count (CBC) and biochemistry panel. The CBC showed a mild leukocytosis [23.60 × 10⁹/L, reference range (RR): 1.99 to 23.00 × 10⁹/L] (9) with frequent reactive lymphocytes and toxic heterophils, suggesting current inflammation or infection. The total solids were slightly increased (66 g/L, RR: 36 to 64 g/L) (8), likely due to mild dehydration. The biochemistry panel revealed an elevated aspartate aminotransferase (AST, 155 U/L, RR: 0 to 77 U/L) (9), most likely due to tissue damage but muscle and liver damage could also be considered. Whole body two-view (dorsoventral and lateral horizontal) radiographs were unremarkable other than the soft tissue swelling on the right eye. Fine-needle aspiration of the mass was declined by the owner. Attempt to surgically remove the mass in its entirety for histopathological examination was elected.

The lizard was premedicated with butorphanol (Torbugesic; Fort Dodge Animal Health, Fort Dodge, Iowa, USA), 1 mg/kg body weight (BW), IM, and induced with propofol (Rapinovet; Schering Canada, Pointe-Claire, Quebec), approximately 10 mg/kg BW, IV, in the ventral caudal (tail) vein to effect, and later intubated with a 2.0 mm inner diameter uncuffed endotracheal tube. General anesthesia was maintained with 3% sevoflurane in oxygen (1 L/min). Hydration was provided with Lactated Ringer’s solution (Baxter, Toronto, Ontario), 10 mL, SQ, and ceftazidime (Fortaz; Glaxo-SmithKline, Mississauga, Ontario), 20 mg/kg BW, IM in the left antebrachium. Thermal support was provided via a forced warm-water blanket. Body temperature was monitored using a handheld digital thermometer. Anesthetic monitoring included a Doppler flow detector (model 811-B, 9.5-MHz probe; Park’s Medical Electronics, Aloha, Oregon, USA) placed under the sternum.

The anesthetized lizard was placed in a left lateral oblique position and the surgical site was aseptically prepared. A medial canthotomy of 5 mm length was performed using iris scissors, and extended the surgical field boundary. The mass was freed from its surrounding tissue attachments using both sharp and blunt dissection. Once released, the mass was completely excised together with the third eyelid using a #11 scalpel blade. The resected mass was fixed in 10% neutral buffered formalin and submitted for histopathological evaluation. Hemostasis was maintained using bipolar cautery (Ellman Surgitron Unit; Ellman International, New York, New York, USA) and surgical gel foam (Surgifoam Ethicon; Johnson & Johnson, Somerville, New Jersey, USA). The incision was closed using 5-0 polydioxanone (PDS, Ethicon; Johnson and Johnson, New Brunswick, New Jersey, USA) in a vertical mattress everting pattern. Meloxicam (Metacam; Boehringer Ingelheim, Burlington, Ontario), 0.1 mg/kg BW was given intramuscularly. The lizard recovered from surgery and anesthesia uneventfully. The lizard was discharged the following day after being gavage fed with 6 mL of a critical care formula (Emeraid^® Omnivore; LafeberVet, Cornell, Illinois, USA). Home care included ceftazidime (Glaxo-SmithKline), 20 mg/kg BW, IM, once every 72 h for 30 d and meloxicam (Boehringer Ingelheim), 0.1 mg/kg BW, IM, once every 24 h for 5 d.

The tissues were routinely processed for histology and stained with hematoxylin and eosin. The mass was infiltrative, non-encapsulated, poorly demarcated, and extended to all lateral and deep surgical margins. Cells were spindle or stellate shaped and arranged in loose streams and sheets. Each cell was surrounded by varying amounts of fine, lightly eosinophilic, myxoid matrix. The cells had poorly demarcated cytoplasmic boundaries that merged with the surrounding matrix and a pale eosinophilic cytoplasm. Nuclei were centrally located and ranged from small and spindle-shaped to large and round. Anisokaryosis was 6-fold and the mitotic rate was 20 mitoses per 10 high power fields. There were up to 3 multinucleate neoplastic cells in each high power field (400×). There were focal regions containing heterophils and hemorrhage. A diagnosis of pleomorphic myxosarcoma was made (Figure 2).

Figure 2.

Photomicrograph of myxosarcoma with neoplastic spindle cells separated by myxomatous intercellular matrix. Hematoxylin and eosin, ×400. Bar = 50 μm

The lizard was returned for adjunct therapy. On physical examination, the right eye appeared mildly swollen, particularly along the lower palpebrum, with mild epiphora. The sutures were intact. The lizard was able to open the affected eye, and the eye appeared functional.

The lizard was anesthetized using the same sedation and anesthesia protocol as described before. Strontium plesiotherapy at a dose of 100 Gy/site was used, by direct contact of radioactive strontium-90 (⁹⁰Sr) probe to the surface of the surgical scar at 5 mm overlapping space intervals and into surrounding normal palpebral tissue. The lizard was given 15 mL Lactated Ringer’s solution (B. Braun Medical, Irvine, California, USA) with B-12 vitamin, 1 mL, SQ, meloxicam, 0.1 mg/kg BW, SQ, and ceftazidime 20 mg/kg BW, IM (right antebrachium). Following the procedure the lizard was recovered in a similar environment as his previous surgery. The lizard was sent home the same day on meloxicam, 0.1 mg/kg BW, IM, q24h for 4 d, with instructions for a recheck in 1 wk.

At recheck examination, the owners indicated they had noticed a small scab on the right upper eyelid a few days after treatment, but it had fallen off prior to the recheck. On physical examination, the lizard was quiet, alert, and responsive. He had gained 32 g in body weight compared with the previous visit. The right eye was still mildly swollen, had no discharge, and the sutures were intact. The lizard was able to open both eyelids well.

The lizard was returned 4 wk post-radiation treatment for another recheck examination and suture removal. Since the last visit, the lizard had been doing very well. The lizard’s activity level, appetite, and bowel movements were normal. Occasionally, the owner noted that the lizard opened his right eye only about 80% of the time. On physical examination, the lizard was bright, alert, and responsive. Body weight was maintained. The affected right eye showed dysecdesis and appeared subjectively slightly larger than the left eye. The sutures were removed since the tissue had healed well.

Five months from the initial presentation, the lizard was presented with a 5-day history of a swelling on the dorsal aspect of the right eye. The owner reported the lizard was doing well at home. On physical examination, the lizard was quiet, alert, and responsive. He was in good body condition and had maintained his normal weight (525 g). There was a firm swelling dorsal to the right eye within the lid margins which was located outside the strontium radiation field. The eye appeared to be functional and the eyelids opened and closed without difficulty.

Differential diagnoses for the swelling included local inflammation, infection, or recurrence of the tumor. Fine-needle aspirates (FNA) of the swelling were performed and cytological evaluation was consistent with recurrence of the myxosarcoma. A biopsy was recommended to obtain a definitive diagnosis. The owners elected for a trial anti-inflammatory therapy with meloxicam, 0.1 mg/kg BW, PO, q24h for 7 d to see if there would be any improvement. During a phone conversation, the owner reported no response to meloxicam and the lizard was lost to further follow-up.

Discussion

This report describes the clinical presentation, diagnosis, surgical removal, and strontium-90 plesiotherapy of a pleomorphic periocular myxosarcoma in a bearded dragon. Myxosarcomas in lizards have been reported, but no details of these cases have been described in the literature (2). Four cases were reported in lizards; 2 in Iguanids and 2 in the family Agamidae, which includes the bearded dragon (2).

Neoplasia is becoming more frequently reported in reptiles (2–7). Retrospective studies have been performed to determine the incidence of common cancers in reptiles (3). Skin tumors were common, including cutaneous squamous cell carcinomas, melanomas, fibrosarcomas, cutaneous papillomas, fibropapillomas, lipomas, spindle cell sarcomas, and chromatophomas (2,3). Iris melanoma was reported in 1 gecko (2,3). There are also reports of squamous cell carcinoma of the skin of the eyelid in lizards (8,10).

Myxosarcomas are malignant soft tissue sarcomas of mesenchymal origin that arise from fibroblast precursor cells (11). They can exude a clear mucoid fluid, and are characterized histologically by an abundance of mucopolysaccharide-rich myxoid matrix (11). No exudate was observed in this case and the neoplastic mass was solid in appearance. Myxosarcomas tend to be unencapsulated, poorly circumscribed, locally infiltrative, and rarely metastasize (11).

Soft tissue sarcomas can be difficult to diagnose since they often display overlapping features with a variety of neoplasms, commonly being soft and lobulated, like lipomas (11). Diagnostic work-up involves fine-needle aspirates to rule out an abscess or cyst. Cytological preparation of these smears may be difficult due to the viscous consistency and lack of cells to adhere to the slide. A biopsy with histopathological evaluation is required for a definitive diagnosis of a myxosarcoma, as was performed in this case.

Myxosarcomas are rare in cats and dogs, in which they are most commonly found subcutaneously on the trunk or limbs, but have been reported from the heart, eye, and brain (11). Myxosarcomas are rarely reported in other species, except rabbits and chickens where the etiologic nature is viral (12). Mxyosarcomas have been reported in ferrets (13), horses (14), dogs (15), hedgehogs (16), and hamsters (17). In humans, myxosarcomas are also relatively rare, and tend to arise most commonly from the heart (12).

No grading scheme exists for myxosarcomas in bearded dragons. Histologic grade of the tumor is a key prognostic factor for predicting survival in human and canine patients diagnosed with soft tissue sarcomas, including myxosarcomas (18,19). The grading system used in dogs involves tissue differentiation, mitotic index, and necrosis and applies a grade of I, II, or III to the tumor (20). Grade I tumors have the lowest likelihood of recurrence following excision, although completeness of surgical margins is also an important factor in recurrence (20). They are also unlikely to metastasize (20). Grade II tumors also rarely recur if complete margins are obtained, though they recur more frequently than grade I tumors (20). Grade III tumors are the least common of the soft tissue sarcomas in dogs, but have the greatest potential for recurrence and metastasis (20).

Treatment options include surgical resection, surgical resection followed by radiotherapy, and surgical resection followed by chemotherapy (19). In dogs, surgical resection with radical margins or surgical resection with radiation therapy are common approaches to treatment (19). Radical resection is considered to achieve high rates of cure, with only 20% of canine patients demonstrating recurrence of the neoplasm (21). Radical surgical margins are 3 cm lateral to the tumor and 1 fascial layer deep to the tumor (11). Radiation therapy is often used in combination with surgery, when incomplete excision occurs (15). Radiation therapy was utilized in this case because it was not possible to obtain the recommended surgical margins due to the location of the neoplasm (11). The optimal total radiation dose and fractionation scheme is unknown for canine soft tissue sarcomas but a dose above 50 Gy seems to be necessary to control microscopic disease (15,19). Chemotherapy is generally not effective against soft tissue sarcomas, though it has been attempted in some cases (15). Chemotherapy is commonly used in cases of incomplete resection, high-grade tumors, and metastatic disease (15). The most common and responsive protocols include doxorubicin and mitoxantrone (22). It is difficult to say if 5 months disease-free in this lizard is a success or failure of treatment.

Plesiotherapy, used in this case, involves direct application of a radiation source to a tumor (23). The ⁹⁰Sr ophthalmic probe has a small active area (about 8 mm in diameter) attached to a shielded applicator (24). ⁹⁰Sr emits beta particles with a maximal energy of 2.27 MeV and has a half-life of 29.12 y (24). The maximal radiation dose provided by the probe is delivered at the skin surface with a rapid decrease in dose with depth; < 10% of the surface dose penetrates to a depth of 3 mm (23). Traditional radiation using a megavoltage unit was not feasible due to the small size of the patient and the proximity of the eye. ⁹⁰Sr has been used in the treatment of cutaneous mast cell tumors and squamous cell carcinoma in cats (23,25,26), and various soft tissue sarcomas in dogs (19). Minimal side effects of ⁹⁰Sr application close to the eyelid have been seen in dogs and cats. The most common side effects with close application to the eye in dogs and cats included corneal scarring and neovascularization, conjunctivitis, keratopathy, and later effects such as scleral thinning and focal scleromalacia (26,27). No side effects as a result of the radiotherapy were noted in this lizard. Radiation therapy has also been reported in the treatment of various reptile neoplasms (28,29).

In this case, the location of the tumor around the eye prevented wide surgical excision without compromising the eye and although potential remaining neoplastic tissue was controlled with the local radiation therapy, this proved to have just a temporary (5 months) effect. It is also possible that the radiation probe may not have been applied to the area where the tumor recurred. However, it is most likely that recurrence was due to the locally infiltrative nature of myxosarcomas.

This case reports the antemortem diagnosis, and multimodal treatment approach including surgical removal, and radiation treatment of a periocular myxosarcoma in a bearded dragon. Myxosarcoma should be considered as a differential diagnosis in bearded dragons presented with a periocular mass. CVJ