Australian elapid snake envenomation in cats: Clinical priorities and approach

Artifactually increased serum bicarbonate in a cat with rhabdomyolysis

A 3-year-old male neutered domestic shorthair cat presented with lethargy, hyporexia, and pyrexia of unknown origin. Biochemical analysis using a Beckman Coulter AU480 demonstrated marked increases in creatine kinase and aspartate aminotransferase, indicative of severe muscle injury, with concurrent presumptive myoglobinuria on urinalysis. A marked, non-physiologic increase in measured bicarbonate and resultant negative anion gap was documented; however, calculated bicarbonate obtained via a point-of-care blood gas analyzer was within normal limits. Laboratory error due to interference by lactate dehydrogenase was suspected and supported by the results of subsequent biochemical testing. Artifactual increases in bicarbonate have been documented in cases of rhabdomyolysis in horses, cows, and a bird. However, to the best of the authors' knowledge, this is the first report to demonstrate this spurious change in a cat.

Static anisocoria in cats and dogs with naturally occurring tick paralysis (Ixodes holocyclus)

OBJECTIVE

To characterise the novel occurrence and neuro-ophthalmological features of static anisocoria in cats and dogs with tick paralysis (TP) (Ixodes holocyclus) due to a single tick located remote from the head and neck.

DESIGN

Observational case series with retrospective analysis.

METHODS

Medical records were reviewed from 69 cats and 169 dogs treated for TP from a suburban veterinary hospital in Newcastle, New South Whales, between September 2005 and October 2021.

RESULTS

Anisocoria was observed in 2/18 (11.1%) cats and 3/30 (10.0%) dogs with a single tick located remote from the head and neck. These proportions were not different when compared within species to 4 of 28 (14.3%) cats and 16 of 98 (16.3%) dogs with aniscocoria with a single tick located on the head and neck region (P = 1 and 0.56 respectively). Anisocoria arose from pupillary efferent dysfunction and included unilateral oculoparasympathetic dysfunction (internal ophthalmoplegia) in one dog, unilateral oculosympathetic dysfunction (Horner's syndrome) in one cat and one dog, and a combination of bilateral, but asymmetric, oculosympathetic and oculoparasympathetic dysfunction in one cat and one dog.

CONCLUSION

It is proposed that anisocoria in cases of TP with a tick located remote from the head and neck is due to an intrinsic latent asymmetry in the safety factor for pupillary efferent function that is unmasked by a systemically distributed holocyclotoxin inhibiting neural transmission within this system, and this is the prevailing pathomechanism, rather than a direct local effect, underscoring anisocoria with a tick located on the head or neck.

Mechanical ventilation in snake envenomation of dogs and cats

Envenomation by snakes in Elapidae and Viperidae families have been associated with respiratory failure in dogs and cats. Mechanical ventilation may be required for hypoventilation due to neuromuscular paralysis or hypoxemia due to pulmonary hemorrhage or aspiration pneumonia. Median incidence of dogs and cats with snake envenomation that require mechanical ventilation is 13% (0.06-40%). Standard treatment of snake envenomation in dogs and cats includes prompt administration of appropriate antivenom and management of envenomation complications such as coagulopathy, rhabdomyolysis and acute kidney injury. When mechanical ventilation is required, overall prognosis is good with appropriate treatment. Standard anesthetic protocols and mechanical ventilator settings are generally appropriate, with lung protective ventilation strategies typically reserved for patients with pulmonary disease. Median survival to discharge for cats and dogs with elapid envenomation is 72% (76-84%) with 33 h (19.5-58 h) median duration of mechanical ventilation and 140 h (84-196 h) median hospitalization. This article reviews indications for mechanical ventilation in cats and dogs with snake envenomation, and discusses ventilator settings, anesthetic and nursing considerations, complications and outcomes specific to this disease.

Multiple cranial nerve motor deficits, resembling polyneuritis cranialis, in a cat with hyperthyroidism

A 14 plus-year-old (exact age unknown) neutered female domestic shorthair cat presented with a 6-day history of rapidly evolving difficulty in eating, dropped jaw, protrusion of the tongue, sialosis, change in voice (meow softer and higher pitched) and mild variable pelvic limb weakness. Salient clinical features were a left thyroid nodule, 2/6 systolic cardiac murmur, poor body condition, hypertension, bilateral retinal haemorrhages and an increased total thyroid hormone level consistent with a diagnosis of hyperthyroidism (HT). Neurological examination disclosed mild generalised weakness, bilateral visual deficits attributable to a hypertensive retinopathy and multiple cranial nerve (CN) motor deficits that included; mandibular paresis (CN V), bilateral external ophthalmoparesis (CNs III, IV, VI), bilateral facial paresis (CN VII), dysphagia (CNs IX, X), dysphonia (CN XI) and symmetrical paresis of the tongue (CN XII). Treatment with carbimazole, and subsequently, a modified extracapsular bilateral thyroidectomy resulted in a rapid improvement in neurological signs over 13 days and complete resolution by 100 days post thyroidectomy. To the best of the authors' knowledge, this is the first description of multiple CN motor deficits in a cat with HT and resembles polyneuritis crainialis that has recently been described in human patients with this disorder. It is suggested the underlying pathogenesis is a thyrotoxic polyneuropathy selectively affecting CN motor function, that HT needs to be considered in cats that might present with such signs and that resolution can occur with successful treatment of the HT.

Successful treatment of a potentially fatal eastern brown snake (Pseudonaja textilis) envenomation in a dog with tiger-brown snake antivenom with serial quantification of venom antigen and antivenom concentrations in serum and urine

CASE REPORT

A successfully treated case of eastern brown snake (Pseudonaja textilis) envenomation in a Jack Russel Terrier dog is described with measurement of venom and antivenom concentration pre- and post-treatment. Early presentation, prompt administration of tiger-brown snake antivenom, hospitalisation and critical care monitoring lead to low morbidity and rapid recovery from a potentially fatal envenomation. Retrospective measurement of urine and serum venom and antivenom provided insight into the potential severity of the case and rapid efficacy of antivenom.

CLINICAL SIGNIFICANCE

Potentially fatal brown snakebite cases may initially present with only mild clinical signs despite having high concentrations of venom and potential for fatal outcome. Prompt treatment with antivenom is essential to prevent the development of progressive and fatal coagulopathy and paralysis.

A retrospective evaluation of eastern coral snake envenomation and antivenom administration in cats: 30 cases (2012-2019)

Thirty cats were identified to be have been suspected to have a potential coral snake envenomation after searching medical records from 2012 to 2019 at a university teaching hospital. The records were reviewed and evaluated for signalment, date and time of the snake encounter, elapsed time between encounter and hospital examination, presenting complaint, initial physical examination findings, initial laboratory findings, antivenom dose and duration of administration, adverse reactions to antivenom, additional treatments administered, progression of clinical signs, length of hospitalization, and outcome. Thirteen cats presented with clinical signs consistent with envenomation while 17 cats were treated for possible asymptomatic envenomation, as defined by the owner discovering a live or dead coral snake in their home or on their property. Initial physical examination findings included tachypnea with short shallow breaths and use of accessory muscles; tetraparesis with normal or decreased to absent spinal reflexes; cranial nerve deficits including decreased to absent gag, slow pupillary light reflexes, and absent physiologic nystagmus; and normal or altered mentation. Laboratory findings included hypercapnia, hyperglycemia, hypokalemia, increased aspartate aminotransferase activity, increased alanine aminotransferase activity, echinocytosis, leukocytosis, azotemia, and hyperlactatemia. Twenty-eight cats received antivenom; two cats received two vials while twenty-six cats received one vial. Antivenom reaction was suspected in one cat that developed facial swelling during administration of the drug. Average length of hospitalization was 1 day for cats without clinical signs and 3 days for cats with clinical signs. Twenty-nine cats survived to discharge. Due to the inclusion criteria of the study, cats euthanized on presentation or discharged without receiving antivenom may have been unintentionally excluded from the study. Diagnosis of eastern coral snake envenomation should be suspected in the cat that has acute onset of lower motor neuron neuropathy. Prognosis with treatment is considered good with 97% of cats surviving to discharge. Antivenom reaction occurred in 3.5% of administrations with none being fatal. Monitoring of hypercapnia was critical in making the decision to mechanically ventilate patients. Supportive care that includes antivenom administration, recumbency care, and mechanical ventilation if needed are the mainstays of therapy.