Case presentation
A seven-year-old neutered male American shorthair cat was referred to
the Saitama Animal Medical Center with symptoms of blepharospasm in the
right eye. Ophthalmic examination revealed superficial corneal
ulceration with mild eyelid restriction in the right eye, but no
abnormality was observed in the left eye (Figure 1). Treatment with
antibiotic and hyaluronate eye drops was started, but the corneal
ulceration in the right eye did not improve at follow-up three weeks
later. In addition, entropion caused by eyelid restriction persisted.
Partial right eyelid tarsorrhaphy was performed to treat the corneal
ulcers. However, vision was eventually lost in the right eye due to
severe exposure keratitis caused by complete eyelid restriction, and
resistance to retropulsion of the globe was observed at follow-up.
Orbital disease was suspected from these clinical findings. Ultrasound
examination was performed, but no apparent mass was observed in the
globe or in the orbit. (Figure 2A). Oral prednisolone (5 mg/head, once
daily) was prescribed for suspected orbital inflammation but was
ineffective, and the dose was tapered off and eventually discontinued.
Given the lack of improvement in clinical symptoms by medical treatment,
surgical resection following computed tomography (CT) was scheduled on
day 138 after initial presentation. CT revealed a space-occupying lesion
in the right orbit, with infiltration extending from the eyelid to the
lips (Figure2B). There were no osteolytic lesions in the orbital bone
and no sign of abdominal or thoracic metastasis. Following the CT
examination, orbital exenteration of the right eye was performed. The
orbit contained multiple nodular lesions, and these were removed to the
extent possible. All specimens were fixed in 10% formalin, embedded in
paraffin, sectioned at 4 µm, and subject to hematoxylin and eosin (HE)
and immunohistochemical staining.
Histopathological examination of HE stained sections revealed the
proliferation of atypical spindle tumor cells infiltrating the skeletal
muscle in the orbital tissue with thin collagenous materials between
spindle cells and moderate lymphoplasmacytic cell infiltration
(Figure3A), but there was no invasion into the globe. Neoplastic spindle
cells resemble reactive fibroblasts or myofibroblasts with mild
anisocytosis and anisokaryosis. These spindle cells have a moderate
amount of elongated eosinophilic cytoplasm and ovoid nuclei with finely
stripped chromatin and one to two nucleoli. There were 4–5 mitotic
figures in tumor cells per ten high-power fields. Immunohistochemistry
showed positive staining for smooth muscle actin (SMA) in the tumor
cells (Figure3B). Based on these histopathological findings, the tumors
were diagnosed as FROMS.
After surgery, the mass in the right lip enlarged, leading to feeding
difficulty. A gastrostomy tube was placed under general anesthesia.
Three weeks after surgery, toceranib 2.17 mg/kg was initiated three
times per week as adjuvant chemotherapy. Toceranib administration was
continued for one month. However, the residual tumor continued to
increase in size, and adjuvant chemotherapy was deemed ineffective and
was discontinued. Subsequently, bleeding from the tumor occurred, which
severely deteriorated the cat’s quality of life. Eventually, the cat
died four months after surgery, 257 days after initial presentation.