Retrobulbar thrombus in a cat with systemic hypertension

Abstract

This report describes a 14-year-old neutered male Norwegian Forest cat that was evaluated for a complaint of inappetence, lethargy, and ocular protrusion with third eyelid prolapse. The systemic blood pressure was elevated at 205/129 mmHg. Fundic examination revealed severe retinal hemorrhage in both eyes. Based on an ultrasound study of the retrobulbar area, a thrombus caudal to the right globe was suspected. Over 18 days, the cat exhibited significant clinical improvement as well as good blood pressure control. To our knowledge this is the first report of a retrobulbar thrombus in a cat with systemic hypertension.

Systemic hypertension is a commonly recognized medical condition usually associated with chronic renal disease or hyperthyroidism. This rise in arterial pressure causes or accelerates changes in the vascular walls of the target organs, such as the kidney, heart, eyes, and brain. ¹ There are also reports of hypertension in cats with hyperaldosteronism, pheochromocytoma, diabetes mellitus, erythropoietin treatment, and chronic anemia. ^2–5 The term ‘primary hypertension’ has been used in the past, ⁵ but this term has been replaced with the term ‘idiopathic hypertension’ when an underlying cause cannot be identified. ² Systemic hypertension appears to be recognized most often in cats over 10 years of age. ⁵ Consecutive systolic blood pressure readings greater than 170 mmHg recorded in a relatively stress-free situation are diagnostic in cats and indicate the need for antihypertensive therapy. ⁶

The physiologic mechanism of blood pressure elevation in renal disease is not completely understood. Increased blood volume secondary to either a maladaptative increase in renin secretion or inability of the kidneys to process electrolytes and fluids properly, may lead to increased venous return of blood to the heart, possibly producing a compensatory increase in cardiac output. Hypertension is a common sequel to renal disease in cats and dogs, affecting as many as 61% cats. ⁷

Systemic hypertension can lead to left ventricular hypertrophy in cats. Moreover, in response to chronic pressure overload, left ventricular wall thickness will increase proportionally to the blood pressure to maintain normal wall stress. Cardiac abnormalities occur in 80% of hypertensive cats, and the clinical signs include systolic murmur, gallop rhythm, arrhythmias, cardiomegaly, and hemorrhage, causing epistaxis and strokes. ^2,8

Ophthalmologically, systemic hypertension produces lesions in the retina, choroid, and optic nerve head; this can include a wide range of lesions, from slight vascular narrowing to severe visual loss due to ischemic optical neuropathy. ⁹ Ocular lesions are observed in many cats with hypertension, although prevalence rates for ocular injury vary. In one study, 100% of cats with systemic hypertension had hypertensive retinopathy, and 83.3% of these cats were presented for acute onset of blindness. ¹⁰ Retinal detachment is the most commonly observed finding. Hypertensive ocular injury has been reported at systolic blood pressure as low as 168 mmHg. ¹¹

Neurologic signs of hypertensive encephalopathy have been reported in 46% of hypertensive cats. ¹⁰ Clinical signs include head tilt, ataxia, depression, disorientation, and seizures. ⁵

Therefore, a complete physical examination, including funduscopic evaluation, cardiac auscultation, and neurologic examination, should be performed in all hypertensive cats. ²

Blood pressure determination is fraught with problems at the clinical level. Direct blood pressure determination, utilizing an intra-arterial catheter, is not practical in the primary care setting. Indirect blood pressure determination used by veterinary practitioners is based on Doppler or oscillometric technology. A recent study of three veterinary oscillometric units did not find values that correlated highly with direct-determined values. ⁷ This problem is compounded by environmental factors that can affect the readings. Domestic cats as a species are subjected to stress responses that affect white blood cell counts and differentials, blood glucose levels, heart rate, respiration rate, and body temperature. Blood pressure is often elevated in cats that ride in an automobile, are placed in non-home environments, and are subjected to medical examinations. Therefore, blood pressure determinations made in veterinary hospital settings must be interpreted in light of equipment shortcomings, environmental factors, and clinical findings.

A 14-year-old, 4.2 kg neutered male Norwegian Forest cat was presented with a history of inappetence and lethargy during the past 3 days. The owners noted gross abnormalities in its right eye. Upon physical examination, the cat was found to be hypertensive (blood pressure 205/129 mmHg; reference interval (RI) 100–160 mmHg/60–100 mmHg). The HDO™ (S+B medVET) oscillometric blood pressure monitor was used for this and subsequent blood pressure measurements. The rectal temperature was 38.7°C. No abnormalities were detected during physical examination except severe retinal hemorrhage in both eyes (Fig 1), and a bulging right eye with a prolapsed right nictitating membrane (Fig 2). Tonometry of the right eye revealed intraocular pressure of 21 mmHg (RI 15–25 mmHg). An ultrasound study of the retrobulbar area was performed and revealed a mass caudal to the right globe (Fig 3). Differential diagnoses included retrobulbar abscess, neoplasia, and thrombus.

Fig 1.

Hemorrhage can be seen dorsal to the optic disk.

Fig 2.

Marked prolapsed of the right third eyelid was present.

Fig 3.

The mass (arrow) is seen on day 1 as a hyperechoic area immediately adjacent to the globe and caudal to it.

The cat had leukocytosis (41.9×10⁹/l; RI 5.5–19.5×10⁹/l), thrombocytopenia (90.0×10⁹/l; RI 200–500×10⁹/l), and a mild regenerative anemia (packed cell volume: 27%; RI 30–45%). Serum biochemistry tests were normal, including creatinine (123.7 μmol/l; RI 53–212 μmol/l) and total T₄ (31.5 nmol/l; RI 12–60 nmol/l). The glucose was slightly above normal (9.52 mmol/l; RI 3.6–9.4 mmol/l).

Due to the possibility of a retrobulbar abscess, the cat was sedated with propofol (4 mg/kg intravenous (IV) to effect with additional boluses given as needed). A 4.0 mm cuffed endotracheal tube was placed to the level of the thoracic inlet, and 100% oxygen administered through it. An incision was made at the right angle of the jaw, but there was no discharge present. Skull radiographs revealed swelling of right eye without boney involvement (Fig 4a, b).

Fig 4.

(a) A ventrodorsal (VD) view of the skull shows soft tissue swelling is seen in the right orbit. (b) An oblique lateral of the skull also shows the soft tissue swelling of the orbital area.

In order to decrease the blood pressure, nitroglycerin 2% ointment (q 12 h transdermally) and amlodipine (1 mg q 24 h per os (PO) were given. In addition, due to the leukocytosis, enrofloxacin (2.5 mg/kg q 12 h subcutaneously (SC) was included in the treatment protocol. After 48 h (day 2), minimal improvement of the bulging of the right eye was observed; however, the nictitating membrane was less prolapsed. Retinal hemorrhage had not changed, but there was no evidence of retinal detachment. The blood pressure was measured at 195/157 mmHg. After 96 h (day 4), another ultrasound study of the retrobulbar area was performed, and the mass caudal to the right eye was estimated to be 50% of its original size (Fig 5). At that time, the cat was discharged with an ophthalmic ointment for lubrication of the cornea and amlodipine (1 mg q 24 h PO). At day 7, the cat was rechecked. The appetite was reported to be improved, and the activity level had increased. Systemic blood pressure was measured at 197/108 mmHg. The ultrasound study revealed the mass caudal to the right eye was 25% of its initial size (Fig 6). Amlodipine was increased to 1.25 mg q 24 h PO. At day 11, the appetite and activity level were good, and the cat had gained 0.2 kg since the first examination. During physical examination, there was still some hemorrhage in both eyes, and the blood pressure was measured at 179/92 mmHg. Benazepril was added to the treatment regimen (2.5 mg q 24 h PO). By day 18, blood pressure was measured at 180/102 mmHg, and the mass caudal to the right globe was not seen ultrasonographically (Fig 7). His right eye appeared grossly normal (Fig 8). The fact that the ophthalmic bulging went away in less than 3 weeks without the use of chemotherapy drugs is strong evidence that it was not a tumor.

Fig 5.

On day 4 the mass is smaller than on day 1.

Fig 6.

On day 7 the mass is smaller than on day 4.

Fig 7.

On day 18 the mass is no longer found with ultrasound.

Fig 8.

On day 18 the globe was no longer protruding, and the third eyelid was normal in position.

Because renal disease or hyperthyroidism was not diagnosed based on blood tests, another cause for the systemic hypertension was sought. Plasma was submitted to for an aldosterone level. The result was slightly out of the RI (393 pmol/l; RI 194–388 pmol/l). This value is not likely to be significant because a study of 20 cats with aldosterone-secreting tumors had values ranging from 800 to 43,000. In addition, abdominal ultrasound did not reveal enlargement of either adrenal gland.

Amlodipine and benazepril were continued, and a 3-month recheck was requested.

Three months after initial evaluation, the owners did not report any signs of recurrence of clinical signs or behavioral changes.

This is the first reported case of retrobulbar thrombus formation secondary to systemic hypertension. It lengthens the differential list for retrobulbar mass causing ocular protrusion with third eyelid prolapse.

The cause for hypertension was not detected. ⁵ However, International Renal Interest Society (IRIS) stage 1 and stage 2a renal disease are accompanied by normal creatinine values. Therefore, further tests, including urine protein:creatinine ratio, renal ultrasound, and renal scintigraphy, might have revealed early renal disease, the most common cause of systemic hypertension in cats. Client factors prohibited us from performing these tests (finances, early concern for a poor prognosis, and major health problems of one owner). Hyperthyroidism was reasonably ruled out based on negative thyroid palpation, a normal total T₄ value, and lack of appropriate clinical signs. An aldosterone-secreting tumor was unlikely due to its rarity in the cat and an aldosterone level not consistent with known cases.

The blood pressure values (195/157) on day 2 were not sufficiently reduced; however, no increase in the dose of amlodipine or additional hypotensive drugs was prescribed. This decision was based on several clinical factors. The cat was quite agitated at this visit so the inherent inaccuracies of oscillometric blood pressure determination were likely magnified. The values were subjectively determined to be falsely elevated based on a perceived stress response and because ocular findings were improved; the nictitating membrane was less prolapsed and there was no evidence of progressive retinal hemorrhage or the onset of retinal detachment.

Monitoring intervals for the cat's blood pressure were not ideal. Although 48 h rechecks were requested, for various reasons listed above, the owners did not return at the times requested. Clinical practice sometimes dictates that we work under less than ideal conditions.

This case appears to be unusual because of the presumed retrobulbar thrombus associated with systemic hypertension and massive bilateral retinal hemorrhage.