Sooty was a 13-year-old, female neutered domestic shorthair cat. She had been owned for six years during which time she had not been vaccinated or wormed. She was an only cat and spent most of her time outdoors. Her diet consisted of various brands of tinned cat food and she weighed 3.2 kg. She had no known previous medical problems and was not taking any medication at the time of referral.

Clinical history

Sooty was referred to the Feline Centre with a four-week history of progressive lameness. On initial presentation to the referring veterinary surgeon a month previously, Sooty was described as having a `drunken' hind limb gait with frequent stumbling. She was having difficulty with jumping and climbing the stairs. At this time the only abnormality noted on clinical examination was swelling of antibiotics, (clavulanic acid potentiated amoxycillin, 50 mg twice daily for five days).

Sooty made no improvement on this treatment and was re-presented the following week. She now had marked right hind limb lameness and pain on lumbosacral palpation. Radiography of the right stifle and lumbar spine revealed no abnormalities at this time. A course of corticosteroids (prednisolone, 2.5 mg twice daily) and antibiotics (enrofloxacin 15 mg once daily) was prescribed.

A solitary mass approximately 1.5cm in diametre is present in the caudal lung field

A very large bladder is present (presumably as Sooty was in too much pain to urinate frequently). The abdomen is otherwise unremarkable radiographically

Profound periosteal new bone formation is present together with areas of osteolysis in the distal femor and proximal tibia on the left stifle

During the following week Sooty's condition continued to deteriorate. She became very weak and uncomfortable on both hind limbs and a lameness was now present in the left forelimb. At this time Sooty was referred to the Feline Centre at Bristol . The owners noted that over the course of the last month Sooty had remained fairly bright but her appetite had steadily deteriorated. She had become increasingly sedentary and now would hardly walk at all. She would not even stand up to urinate or defecate. The owners felt that Sooty was in substantial pain as she would no longer tolerate being handled.

Clinical examination

On clinical examination Sooty was alert but very reluctant to move and resented any form of handling. She was eventually encouraged to walk a short distance which she did with a very stiff, stilted gait holding her stifles flexed and her back arched. Her mucous membranes were pink with capillary refill time less than two seconds. Her heart rate was 200 beats per minute and her respiration rate was 24 breaths per minute. This heart rate is slightly higher than would be expected for a resting value but the respiratory rate is within the normal range. Much of the clinical examination was compromised by the extreme pain induced by any palpation. It was noted, however, that both stifles were grossly swollen and there was very poor muscle condition of all limbs. The majority of the neurological examination could not be performed adequately, but proprioceptive reflexes were found to be normal.

Investigation

A percutaneous fentanyl patch was applied for pain relief pending radiography. The patch releases a potent opioid painkiller into the systemic circulation via diffusion through the skin. Unfortunately this failed to control Sooty's pain and further handling proved a major problem. Sooty was anaesthetised for further investigation.

Unpremedicated halothane via a gas chamber was used to minimize the need for further handling. Sooty was intubated and anaesthesia maintained using halothane. Under anaesthesia it was clear that both stifles were grossly swollen. This swelling was firm and extended along the distal third of the femurs and the proximal third of the tibias and fibulas. Movement was significantly reduced in the stifle and hock joints. The muscles of all four limbs were profoundly atrophied and several firm, roughly spherical masses could be palpated within the muscle bellies. One mass approximately 1 cm in diameter was present in the triceps muscle of the left fore limb and two masses were present, both approximately 1.5 cm in diameter, in each of the gastrocnemius muscles of the hind limbs. All of the digits of the left fore and left hind limbs were swollen with bleeding from the nail beds.

Results

Blood was collected for routine biochemical and haematological analysis and for FIV/FeLV screening. Samples were also submitted for antinuclear antibody and rheumatoid factor assay to try to rule out immune-mediated disease. Both stifle joints were aseptically prepared and a sample of joint fluid (synovial fluid) aspirated. This yielded an excessive volume (0.4 ml) of blood-tinged synovial fluid. The fluid was submitted for cytology and for bacterial culture and sensitivity. Multiple fine needle aspirates were taken from the masses in the gastrocnemius and triceps muscles.

The presence of multiple digital lesions along with the muscle masses was suggestive of metastases from a pulmonary neoplasia such as a carcinoma. We also considered the possibility of hypertrophic pulmonary osteopathy (HPOA). This is a condition in which a pulmonary (orProfound periosteal new bone formation is present together with areas of occasionally abdominal) mass leads to secondary periosteal new bone osteolysis in the distal femor and proximal tibia on the left stifle formation in the limbs. The cause of these secondary bony changes is unknown but they often result in intense pain and swelling of the limbs. Survey thoracic and abdominal radiographs were therefore taken as well as lateral stifle and anterioplantar/palmar digital views.

Conclusions

The results are consistent with advanced epithelial cell neoplasia with evidence of spread throughout the body. Sooty was suffering from intractable pain, and the prognosis for her condition was extremely poor. After discussion with her owners it was decided to euthanase her while still under her anaesthetic.

Discussion

The results were consistent with neoplasia of epithelial cell origin (for example squamous cell carcinoma or adenocarcinoma), with lesions present in the lungs, digits, stifles and muscles. No pulmonary signs had been present clinically, but this is not unexpected given that the lesion was focal and relatively small.

`Lung-digit syndrome' is a recognised condition of cats in which a primary pulmonary neoplasm metastases to the digits, often resulting in osteolysis of the phalanges. Invariably multiple digits are affected on multiple limbs. In Sooty's case the digital metastases were accompanied by metastases to other sites which is also a recognised presentation. Discrete masses within limb muscles have been described but the stifle changes are unusual. Hypertrophic pulmonary oesteoarthropathy could be ruled out since the bony changes seen in this condition are purely proliferative and usually originate distally, gradually spreading proximally up the limbs. Profound osteolytic and proliferative lesions such as Sooty's are usually associated with primary neoplasia rather than metastases. We can therefore not rule out the possibility that Sooty was suffering from a primary hone tumour affecting the stifles with metastases to the lung. It is also conceivable that Sooty may have had two separate neoplastic conditions ie, a primary lung tumour with digit and limb muscle metastases plus a separate primary bone tumour affecting the stifles. The concurrent existence of multiple neoplasms within one individual is uncommon, though Sooty was FIV-positive, which does predispose to neoplastic states via immunosuppression. Unfortunately post rnortem examinations were not possible so the nature of the pulmonary and bony lesions was not identified. Sooty was suffering from a particularly unusual form of neoplasia. There was multiple organ involvement and the radiological changes were dramatic and indicative of an advanced neoplastic process. The prognosis was extremely poor and given that Sooty's condition was intensely painful, euthanasia was deemed to be the kindest treatment option in this case.