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Veterinarian Technician July 2005 (Vol 26, No 7)

Case Report: An Unexpected Finding in a "Clinic Cat"

by Sandra Rhodes, RAHT

    Dash, an 11-year-old, spayed domestic short-haired cat, has been the "clinic cat" at Nanton Veterinary Clinic since she was 6 weeks of age. The staff adopted her on a cold winter night after a local police officer found her shivering and alone outside a local bar.a As she reached her senior years, Dash required minor dental care and treatment for cystitis (bladder inflammation) but otherwise has been healthy.

    Clinical history

    On January 21, 2004, the staff noticed that Dash was becoming restless, eating less, and drinking and urinating frequently. Results of a urinalysis revealed the following:

    Specific gravity: >1.060 (normal: 1.020 to 1.040)

    Chemstrip: 9 R (Roche)

    pH: 6 (normal: 5.5 to 7)

    Protein: 100 mg/dl

    Glucose: Negative

    Ketones: Negative

    Bilirubin: Negative

    Urobilinogen: Negative

    Blood: 50 erythrocytes per microliter (hemoglobin)

    Sediment:

    — Red blood cells: Few

    — White blood cells: Few

    — Transitional and squamous epithelial cells: 4 per low-power field; coarse and fine granular casts: 2 to 3 per high-power field

    — Bacteria: ++

    — Struvite crystals: 2 to 3 per low-power field

    Based on laboratory findings, a diagnosis of bacterial cystitis was made; this was the fourth time in 2 years that Dash was diagnosed with this condition. The prescribed treatment was enrofloxacin (25 mg PO sid for 10 days).

    On January 23, the presence of uroliths was investigated because struvite crystals were found in her urine sediment during each occurrence of cystitis. Abdominal radiographs were obtained and found to be inconclusive; therefore, a pneumocystogram, which would yield detailed information about the bladder, was scheduled. If this had been a client's geriatric pet, the normal protocol would have been to conduct a diagnostic blood screen before anesthesia; however, because Dash was a clinic cat, it was not deemed necessary because a blood screen had been obtained on July 30 of the previous year. Results had been normal except for an elevated T4 concentration (52 nmol/L [normal: 18 to 40 nmol/L]). It was felt that Dash was healthy enough for a brief anesthetic.

    Dash's heart rate was 126 bpm (normal: 120 to 140). A repeat panel that had been obtained on August 9 of the previous year indicated a T4 level of 46 nmol/L, which was slightly elevated, but Dash was not exhibiting signs of hyperthyroidism (e.g., poor haircoat, weight loss). Because Dash is always purring, it was difficult to properly auscultate her heart; only a loud rumble could be heard when listening. Efforts to stop her purring were unsuccessful. If the heartbeat cannot be heard, cardiac abnormalities, such as irregular heart sounds, abnormal rhythm, or increased or decreased heart rate, cannot be detected. If such abnormalities are missed, there is a risk of cardiac events precipitated by anesthesia such as ventricular arrhythmia or cardiac arrest. Dash's heart rate was 150 bpm under anesthesia, with no abnormal heart sounds. A heart rate of 150 bpm after induction is not unusual in a cat.

    Sedation with 1 mg butorphanol, 0.25 mg acepromazine, and 0.19 mg atropine IM was initiated before mask induction with halothane anesthesia. The pneumocystogram yielded no abnormal findings, and treatment with enro­floxacin was continued. Dash seemed to improve with antibiotic therapy, and although she was lethargic the frequent urination subsided.

    On the morning of February 3, a technician noticed that Dash's health had deteriorated. After close examination by a veterinarian, it was discovered that Dash was no longer purring, her mucous membranes were slightly cyanotic, her respiration was rapid, and her heart rate had increased to 180 bpm. She also had vomited. The staff's initial worry was that the pneumocystogram had been conducted without a blood screen before general anesthesia.

    Chest radiographs were obtained, and the results were unremarkable. A geriatric blood panel, including a T4 level, was obtained. Results showed a very high T4 concentration (72 nmol/L) and an elevated alanine aminotransferase (ALT) level (117 IU/L [normal: 34 to 106 IU/L]). The T4 level was diagnostic of hyperthyroidism. This finding surprised everyone because hyperthyroid cats typically are thin and have a poor haircoat. Dash weighed 12 lb (5.5 kg) and had shiny fur and a normal appetite.

    Treatment

    In-Clinic Therapy

    On February 4, treatment with an antithyroid medication, methimazole (5 mg PO bid), was initiated. The two veterinarians who owned the practice discussed available treatment options, including radioactive iodine 131 (131I), surgical removal of abnormal thyroid tissue, and antithyroid medication.

    On February 5, it was decided that the best option for Dash was 131I treatment. The University of Saskatchewan's Western College of Veterinary Medicine (WCVM) in Saskatoon was contacted to add Dash's name to a waiting list for treatment.

    On February 25, Dash began vomiting and appeared unwell; therefore, the methimazole was discontinued. During the first weeks of treatment, gastrointestinal upset is a common side effect of methimazole; therefore, recommendations were followed to temporarily discontinue the drug for 10 days and resume administration at a lower dose. Dash's packed cell volume was 42%, her total protein was 6.8 g/L, and the differential also was normal.

    A few days later, the staff was notified that Dash was to be admitted to WCVM on March 8. Dr. Sue Taylor, a senior internal medicine clinician at WCVM, advised that it was not necessary to resume treatment with methimazole before admission for 131I treatment. The Nanton staff was given information about hyperthyroidism and what to expect from treatment along with a caution that kidney disease or serious heart disease may preclude treatment.

    131I Treatment at WCVM

    Dash was content during her 7-hour car ride to Saskatoon, and she ap­peared content during her examination by fourth-year veterinary student Christy Hitesman. Dash purred, rubbed against Christy, and laid calmly on the examination table. This type of behavior is unusual because hyperthyroid cats tend to avoid any type of physical contact. Dr. Taylor also examined Dash and was concerned because her heart rate was 240 bpm with an occasional gallop rhythm. A thyroid nodule was palpated, and Dash was noted to be moderately obese.

    Pretreatment studies included a complete blood count, serum biochemistry profile, resting T4 level, an electrocardiogram, cardiac and abdominal ultrasonograms, and a urinalysis. Ab­dominal ultrasonography was conducted and a urine culture obtained because of Dash's history of recurrent bacterial cystitis and the presence of what appeared to be an internal lipoma in the left caudal abdomen. Results of preliminary tests were normal with the exception of the T4 level, which was 109 nmol/L (normal [WCVM]: 13 to 50 nmol/L), and heart rate, which was 240 bpm. These preliminary tests help ensure that patients are ideal candidates for 131I treatment. It was determined that Dash was a good candidate for this therapy.

    On March 12, Dash was given a single subcutaneous injection of 3.3 millicurie of 131I. She spent a restful week in the iodine therapy room. After treatment, strict radiation safety precautions and procedures had to be followed. Cats receiving iodine therapy must be hospitalized until a Geiger counter shows that their surface radiation dose has fallen below a level deemed safe by radiation control officials.1 The hospitalization period was un­eventful. The only follow-up re­quired was a blood test 1 month after treatment to measure T4 concentration.

    Homeward bound

    On March 22, Dash returned to the Nanton Veterinary Clinic. The next day, she wandered throughout the clinic and investigated each room. Although Dash appeared a little skittish from her recent experience, she seemed happy to be home. Results of a blood test conducted on April 14 showed a T4 level of 19 nmol/L, indicating that 131I treatment was successful.

    Case Commentary

    A small number of cats develop "apathetic" hyperthyroidism, which can be indicated by such clinical signs as lethargy, anorexia, and weight loss.2 How­ever, as in this case, some cats show no clinical signs of hyper­thyroidism.

    Hindsight is always 20/20. We realized that we should have obtained a preanesthetic blood screen and were lucky that we had not induced a fatal arrhythmia during general anesthesia. This incident served as a reminder that preanesthetic blood screenings are important, and patients with borderline-normal T4 concentrations require follow-up!

    Radioactive iodine treatment is expensive and is not a consideration for all patients. We were glad this option was available for Dash because she experienced side effects when taking methimazole.

    As geriatric blood screenings in older patients become more routine, feline hyperthyroidism is being diagnosed earlier. When ruling out hyperthyroidism, veterinary professionals should not rely on telltale signs, such as inappetence and poor haircoat. At WCVM, many obese patients that had lost weight secondary to hyperthyroidism were still significantly overweight at the time of presentation.1

    1. Meric SM: Recognizing the clinical features of feline hyperthyroidism. Vet Med 84(10):954-981, 1989.

    2. Panciera DL, Peterson ME, Birchard SJ: Diseases of the thyroid gland, in Birchard SJ, Sherding RG (eds): Saunders Manual of Small Animal Practice, ed 2. Philadelphia, WB Saunders, 2000, p 240.

    aRead about how Dash became the "clinic cat" in our December 2003 issue, p. 869.

    References »

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