Palliative Management of Cancer Pain in a Geriatric Cat

On presentation, Luna was quiet and shy. Vital parameters were within normal limits (temperature, 100.8°F [38.2°C]; pulse, 160 bpm; respiratory rate, 36 breaths per min). She was subclinically dehydrated (5%), and her hair coat was greasy. The right submandibular lymph node was enlarged. BCS was 3/9, which was similar to previous visits, with apparently stable body weight. Systolic blood pressure was 140 mm Hg (reference range, <150 mm Hg). Because Luna refused to walk, mobility could not be assessed.

Oral pain was assessed through gentle palpation of the mandible. Luna showed signs of hyperalgesia (ie, increased pain sensation to a painful stimuli) and clear avoidance of palpation while hissing at the clinician. Because osteoarthritis (OA) was suspected, OA-related pain was assessed using the Client Specific Outcome Measures instrument (see Suggested Reading),¹ which consisted of choosing and scoring 3 activities that were specific to Luna (ie, jumping onto the kitchen’s window sill in the morning, using the litter box after breakfast, jumping onto the bed in the evening). Luna performed these activities with severe, mild, and moderate difficulty, respectively. Although there is currently no validated instrument to assess quality of life that is freely available to veterinarians, a general quality-of-life assessment was performed by evaluating Luna’s ability to perform daily activities, appetite and grooming habits, and social interactions and temperament.^2,3 Because Luna was showing progressively decreased levels of activity and socialization, it was determined that her quality of life was moderately affected.

CBC and serum chemistry profile results revealed mild anemia (hematocrit, 25%; reference range, 28%-47%) and elevated BUN (42.6 mg/dL; reference range, 11.5-30.2 mg/dL) and creatinine (2 mg/dL; reference range, 0.4-1.9 mg/dL) levels. Urine specific gravity was 1.029 (reference range, ≥1.035), symmetric dimethylarginine was 15 μg/dL (reference range, 0-14 μg/dL), and total thyroxine was 1.6 μg/dL (reference range, 1.0-4.4 μg/dL).

Luna was anesthetized for additional diagnostics. Premedication was administered intramuscularly with a combination of acepromazine (0.02 mg/kg) and buprenorphine (0.02 mg/kg). Thoracic radiography and abdominal ultrasonography were performed with the patient under sedation and revealed no evidence of metastasis. Approximately an hour after premedication, general anesthesia was induced with propofol (5 mg/kg IV) and maintained with isoflurane (1.2%-1.3% expired concentration delivered in 100% oxygen using a nonrebreathing circuit). Intravenous fluids (3 mL/kg/hr) were also administered. A firm mass (1.2 × 2 cm) was identified on the right rostral mandible. Oral radiographs revealed marked osteolysis and periosteal proliferation. An inferior alveolar (mandibular) nerve block was performed using bupivacaine 0.5% (see Local Anesthetic Technique for Nerve Blocks). An incisional biopsy was performed at the junction of normal and abnormal tissues and submitted for histopathology. No attempts were made to surgically remove the mass, as the owners did not want to perform any invasive procedures and wished to only confirm diagnosis. Histopathology results were consistent with squamous cell carcinoma.

Opioids are safe at clinically acceptable dosages and are excellent analgesics.⁴ The combination of opioids and acepromazine reduces inhalant anesthetic requirements. Locoregional anesthesia with bupivacaine provides pain relief by blocking sodium channels and the consequent production and transmission of nociceptive stimuli (ie, pain transduction and transmission). Analgesia lasts approximately 6 hours with locoregional bupivacaine.

Luna was hospitalized for 36 hours and maintained on fluid therapy. Pain was assessed every hour for the first 8 hours and every 6 hours thereafter using the Glasgow Composite Measure Pain Scale, which includes evaluation of the cat’s behavior and facial expressions while undisturbed.⁵ A pain scale score equal to or higher than 5 (out of 20) is the recommended cut-off score for intervention (eg, with buprenorphine [0.02 mg/kg IV q6h]). During pain assessment 4 hours after recovery from anesthesia, Luna was tense and crouched, with facial expressions indicative of pain, based on ear position and muzzle shape; pain score was 7/20. Thus, buprenorphine (0.02 mg/kg IV q6h) was administered. In addition, Luna exhibited a normal appetite when offered soft food, suggesting that the previously reported decreased appetite had been due to oral pain, which was attenuated by analgesic management.

The owners opted for palliative analgesic treatment (see Treatment at a Glance), with the aim of improving quality of life. Treatment of cancer was declined after a thorough discussion.

Luna’s potential sources of pain included cancer pain affecting the oral cavity and bone, as well as pain associated with OA, resulting in mixed inflammatory and neuropathic pain. Therapy was planned using a mechanism-based approach (ie, analgesics to counteract inflammatory and neuropathic pain mechanisms). Luna was discharged on long-term medication, including robenacoxib (1 mg/kg PO q24h [see Extra-Label Drug Use]) and gabapentin (10 mg/kg PO q12h). NSAIDs are excellent analgesics for inflammatory pain but are normally contraindicated in cats with CKD; however, recent research has suggested that NSAIDs may be safely administered long-term in cats with stable CKD.^6,7 The decision to initiate NSAID therapy in cats with CKD, however, should be made on a case-by-case basis, and the risks and benefits should be carefully assessed.⁸ In Luna’s case, the benefits of NSAID therapy were determined to outweigh the risks, particularly because proper nutrition and hydration were being maintained. Gabapentin blocks Ca⁺² channels and reduces neuronal excitability, and this drug has been shown to provide analgesia in cats with OA and is indicated in conditions that cause neuropathic pain.⁹

Nonpharmacologic therapy in the form of environmental enrichment was also initiated and included play sessions (15-20 minutes of access to the backyard under supervision twice daily), brushing (10-minute sessions twice daily according to Luna’s preference), and providing scratching posts, homemade toys and condos, and steps to give Luna access to windows. Other nonpharmacologic treatment modalities could include acupuncture and/or nutraceuticals (eg, fish oil or green-lipped mussel extract, glucosamine/chondroitin sulfate, polysulfated glycosaminoglycan [extra-label]). Long-term chronic pain management should include treatment of breakthrough pain (eg, administering buprenorphine when oral medications and other treatments are not controlling pain).²

Luna’s needs were approached from a welfare perspective to provide optimal pain management using pharmacologic and nonpharmacologic options.^2,3

Luna’s prognosis was guarded to poor. Recheck visits were performed monthly. Despite pain management, disease was progressive and resulted in pathologic mandibular fractures. Luna’s quality of life could no longer be maintained as an outpatient, and she was euthanized 8 weeks after presentation (see Take-Home Messages).