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Hyperthyroidism is one of the most common endocrine diseases affecting older cats. Hyperthyroidism typically results from a functional thyroid adenoma (98%) or a carcinoma (1-2%). In the euthyroid cat the thyroid hormones are released from the thyroid gland in response to thyroid stimulating hormone (TSH). The hormones circulate as thyroxine (T4) and the biologically more active triiodothyronine (T3). Thyroxine (T4) acts as acirculatingreservoir of thyroid hormone and is converted to T3 in response to concentrations of T3.
Functional neoplastic tissue breaks away from the negative feedback loop and overproduces thyroid hormones despite low concentrations of TSH. The thyroid glands are bi-lobar and located on either side of the trachea, normally distal to the larynx. There are two associated parathyroid glands. One is extracapsular and situated adjacent to the thyroid capsule at the cranial pole while the other is surrounded by the thyroid tissue and is found at the caudal pole. Cranial pole of the capsule a branch of the carotid, the cranial thyroid artery, supplies each thyroid gland. Recurrent laryngeal nerves run close to the thyroid glands.
The epidemiology of hyperthyroidism in cats remains unclear and no single underlying cause has been identified. It is likely that diet and the environment play a role. In humans, hyperthyroidism is twice more likely to occur in humans with dietary iodine deficiency. However the pathophysiology of hyperthyroidism development in humans is different humans develop autoantibodies against the TSH receptor, whereas this is not seen in cats. The second most common cause of human hyperthyroidism is toxic nodular goitre one or more hyperfunctioning adenomas similar to cats...
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Chronic nasal disease in cats maybe caused by various aetiologies including infection, inflammatory and neoplastic disease. Definitive diagnosis can require advanced imaging and biopsy, yet despite utilisation of these modalities and depending on the disease process, treatment ultimately is about long term management rather than cure in many cases.
- Viral e.g. Feline Herpesvirus & chronic rhinosinusitis
- Fungal e.g. Cryptococcus, Aspergillus
- Tooth root abscess
- Oronasal fistula
- Nasopharyngeal polyp
- Chronic lymphocytic plasmocytic rhinitis "nasal IBD"
- Foreign body
- Squamous cell carcinoma
- Choanal atresia
- Nasopharyngeal stenosis
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Pleural effusions may occur in cats due to the following mechanisms:
- Increased capillary hydrostatic pressure e.g. congestive heart failure
- Altered lymphatic drainage e.g. neoplasia within the chest cavity
- Altered capillary integrity e.g. feline infectious peritonitis (FIP), inflammation or
- Decreased colloidal oncotic pressure e.g. hypoalbuminemia.
Fluid can be characterized based on cell numbers and types of cells, the protein content of the fluid, triglyceride and cholesterol content. Traditional fluid types include transudates, modified transudates and exudates. There is often cross-over between categories...
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The feline liver is susceptible to disease as it has limited conjugation capabilities. It can only conjugate to cholic acid with taurine. Also, due to deficiencies in glucuronyl transferase, the feline liver performs limited glucoronide conjugation, the major route for elimination of salicylates, morphine derivatives, diazepam derivatives, phenols, pyrethroids and benzoic acids.
Additionally, the feline liver has high activity of hepatic transaminases and deaminases, requiring a high dietary protein requirement. Cats are unable to down regulate these enzymes in times of limited protein intake (e.g. starvation or reduced appetite), predisposing to the development of diseases such as hepatic lipidosis (HL).
Anatomically, the major pancreatic duct joins the common bile duct from the liver before entering the duodenum, predisposing to ascending infection from the gastrointestinal tract...
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Cats with urethral obstruction are one of the true feline emergencies. They may present with marked hyperkalaemia. Cardiovascular protection is paramount via administration of calcium gluconate (1-1.5 mls/kg 10% calcium gluconate) to re-establish membrane excitability. If given too quickly it will cause further bradycardia and ventricular arrhythmias. Calcium gluconate will not lower serum potassium concentration, it's benefit is predominantly in stabilising the patient prior to administration of treatments that will redistribute or excrete potassium.
Intravenous fluid therapy and relieving the obstruction are likely the two most important factors in resolving electrolyte derangements.
Redistribution of potassium using dextrose (0.5 g/kg IV bolus) increases endogenous insulin and moves potassium intracellularly. Insulin ((rapid acting insulin 0.25-0.5 IU/kg) may also be required and ongoing supplementation with dextrose to prevent hypoglycaemia is important. 2 agonists (e.g. salbutamol) stimulate the Na+/K+ ATPase pump to move potassium intracellularly. Although not evaluated in cats, giving three to four puffs of inhalational salbutamol is a quick and rapid treatment that might be helpful...
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Chronic kidney disease (CKD) is the most common kidney disease in cats, estimated to affect 0.5-1.5% of the general population and 30% of cats over 15 years. The term CKD or chronic renal disease is non-specific, but preferred to "chronic renal failure" or "chronic renal insufficiency" as owners understand the terminology and the negative context imbued by "failure" is avoided.
Guidelines for staging cats with CKDwereestablished by the International Renal Interest Society (IRIS)(http://www.IRISkidney.com) and providea useful classification system for ongoing monitoring and information on expected outcome.CKD stagingis based on serum/plasma creatinine concentration and recently, symmetric dimethylarginine (SDMA) has also been included in the guidelines. It is important to note that the specificity of SDMA has not been tested in large scale prospective studies. A recent study compared SDMA, creatinine and glomerular filtration rate in 49 cats that were normal or had CKD or diabetes mellitus (Brans et al JVIM2020). SDMA was a reliable marker of reduced GFR but superiority of SDMA over creatinine could be demonstrated...
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Initial requirements for patient stabilisation depend on the rapidity of onset, type and underlying cause of the anaemia. Collapsed cats require more intensive and aggressive stabilisation than cats with chronic anaemia who frequently appear cardiovascularly stable (based on heart rate, pulse quality, respiratory rate and systolic blood pressure and general demeanour) despite a low PCV.
Patients with blood loss or hypovolaemia will benefit from immediate intravenous fluid therapy to ensure organ perfusion. Initially this can be administered as crystalloid therapy (40-60 ml/kg) although crystalloids will redistribute rapidly (within 30 minutes). Hypotensive resuscitation maybe useful in patients with marked haemorrhage as aggressive fluid therapy may worsen bleeding. This technique requires invasive monitoring methods (e.g. arterial blood pressure) which are rarely available in general practice.
Synthetic colloids (doses ranging from 2-7 ml/kg in cats) may hold fluid within the vascular space for longer than crystalloid fluids depending on the health of the vascular endothelium. They may be used in combination with crystalloids to maintain adequate plasma volume expansion. Caution should be used when administering these products to patients with a coagulopathy as their effect on coagulation is unpredictable in critically ill patients...
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Feline Infectious Peritonitis (FIP) is a devastating syndrome caused by infection of cats with feline Coronavirus (FCoV) a large, enveloped, positive-sense single stranded RNA virus. A spike protein mediates entry into host cells. Two serotypes are recognized. Type I is associated with most field strains and Type II formed from recombination events between FCoV and Canine Coronavirus. There are differences in transmembrane spike (S) gene and protein. Approximately 40% of cats are reported to be infected with FCoV with prevalence rates increasing to 90% within multicat households, although regional variation is expected.
Typical infection with FCoV results in mild intestinal signs. FCoV was thought to be confined to the intestine, however systemic FCoV infection has been demonstrated in healthy cats. Up to 10% of cats infected with FCoV will develop FIP.
Due to the high prevalence in many areas of FCoV, definitive diagnosis of FIP can be difficult. Making a definitive diagnosis is based on demonstrating appropriate signalment, history and examination findings and interpreting this together with laboratory data.
Cats are typically under 2 years of age and may be from multicat households. There is often a history of recent stress (e.g. neutering, rehoming etc), abdominal distension and dyspnoea. Physical examination findings include pyrexia, jaundice, effusions, uveitis and neurological changes. In a recent retrospective study of pyrexia in 106 cats from a referral centre, 20% of the cats had FIP...
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