Anorexia In Canine and Feline

Anorexia In Canine and Feline: Causes, Symptoms and Treatment

Overview

• Anorexia is a diminished or absent desire to consume food.
• Hyporexia is a diminished desire to eat.
• Dysrexia is a change in appetite or the absence of a stable appetite.
• Anorexia nervosa is a reduction in food consumption, resulting in manifestations such as weight loss, dehydration, nutritional deficiencies, and sarcopenia.

Causes of Anorexia In Canine and Feline

Causes

• Potential signs of a wide range of systemic illnesses.
• Psychological factors, such as food aversion, stress, and changes in routine or surroundings.
• Pain.
• Toxic substances and the undesirable effects associated with drug administration.
• Gastrointestinal and pancreatic disorders.
• Acid-base disorders.
• Organ failure, such as cardiac, renal, and hepatic failure.
• Endocrine and metabolic illnesses.
• Neoplasia.
• Infectious diseases.
• Immune-mediated diseases.
• Respiratory diseases.
• Musculoskeletal illnesses.
• Neurological illnesses.
• Various factors, such as motion sickness and excessive environmental temperature.

Risk factors

• Nausea.
• Pain.
• Dietary modifications.
• Environmental stress.
• Concerns related to palatability, such as anosmia.
• Endocrine variables, including malfunctions in the thyroid and adrenal glands.
• Systemic disease.

Pathogenesis of Anorexia In Canine and Feline

• Appetite regulation is a multifaceted interplay involving the central nervous system, the surrounding environment, and the gastrointestinal tract.
• The hypothalamus and brainstem have neurons responsible for regulating feeding, serving as primary receivers for sensory and metabolic inputs.
• These cellular populations have projections to multiple locations of the brain and demonstrate significant interconnections.
• Various sensory signals have an impact on appetite, encompassing factors such as olfactory perception, gustatory experience, tactile sensation, and thermal properties of food.
• Stomach and duodenum distention can contribute to the modulation of appetite.
• Metabolic signals of hunger and satiety encompass a diverse range of peptides and hormones that are secreted during periods of fasting and feeding.
• Glucose, amino acid, and fatty acid levels in the bloodstream play a role in regulating these sensations.
• Insulin, glucagon, somatostatin, cholecystokinin, peptide tyrosine tyrosine (PYY), and pancreatic peptide provide a centrally mediated effect to reduce appetite.
• Adipocytes produce leptin, which acts on specific receptors in the hypothalamus to increase metabolic activity and suppress appetite.
• Neuropeptide Y released from the gastrointestinal tract after dietary restriction elicits hunger and reduces energy expenditure.
• Ghrelin, a hormone synthesized in the stomach, exhibits prokinetic properties and enhances appetite by suppressing the production of leptin while promoting the development of neuropeptide Y.
• Serotonin is a central mediator through a serotonergic pathway that traverses in close proximity to the ventromedial hypothalamus nuclei, which is known as the satiety center.
• Dopaminergic tracts in the hypothalamus facilitate the control of food intake.
• Environmental factors, such as the specific geographical and temporal aspects of meals, acquired behaviors, and circadian rhythms, regulate appetite.
• Brain lesions that impact the hypothalamus alter appetite.
• Any condition that diminishes cerebral arousal decreases food consumption.
• Proinflammatory cytokine release can lead to hyporexia in animals with inflammatory and neoplastic illnesses.
• Exogenous and endogenous toxins, such as liver and renal failure, cause hyporexia.
• Hyporexia is commonly related to neoplasia, metabolic abnormalities, pancreatitis, and primary gastrointestinal illnesses.
• Fear, pain, and stress decrease appetite.

Symptoms (History & Physical Examination) of Anorexia In Canine and Feline

History

• Refusing food consumption is an often observed initial concern among pet owners, leading to considerable emotional discomfort.
• Owners report a noticeable decrease in body weight as a result of this behavior.

Physical Examination

• The results differ based on the root cause.
• Low body condition score and muscle wasting vary depending on the time during which food intake has been reduced.
• Patients diagnosed with pseudoanorexia may exhibit symptoms such as halitosis, excessive salivation, challenges in grasping or chewing, and odynophagia.

Diagnosis of Anorexia In Canine and Feline

1- From History and Physical Examination

2- Diagnostic Procedures

CBC/BIOCHEMISTRY/URINALYSIS

• Variations in abnormalities across different underlying disorders.
• May be normal.

OTHER LABORATORY TESTS

• The history, physical examination, and preliminary tests may call for additional diagnostic tests to investigate specific disorders.
• To establish a conclusive diagnosis, do heartworm serology, tick serology, retrovirus serology, thyroid level assessment, and histologic/cytologic evaluation of tissue or cell samples.
• Baseline cortisol or adrenocorticotropic hormone (ACTH) stimulation test to exclude the possibility of hypoadrenocorticism, even in the absence of notable laboratory alterations.

Imaging:

• Thoracic and abdominal imaging examinations, such as radiography and ultrasound, are frequently incorporated into the minimal database for the purpose of identifying anatomical or functional problems.
• Videofluoroscopy and endoscopy are potential diagnostic procedures to assess the function and visual characteristics of the pharynx, esophagus, and gastrointestinal tract.

3- Differential Diagnosis

• Pseudoanorexia is a condition in which animals feel hungry but cannot consume food due to disorders that cause dysfunction or pain in the facial, neck, oropharyngeal, and esophageal regions.
• Animals with anosmia frequently demonstrate diminished appetite.

Treatment of Anorexia In Canine and Feline

General

• Immediate consideration should be given to assisted feeding for seriously malnourished patients who have a body weight loss of 10% or more, hypoalbuminemia, low body condition score, indications of muscle wasting, and/or chronic disease processes.
• In patients with good physical condition with a reduced appetite, consider providing assistance with feeding if their food intake falls below their resting energy requirement (RER) over a period of 3-5 days without any signs of improvement.
• The RER can be calculated using the formula RER = 70 x (body weight kg^0.75).
• Avoid force-feeding, especially in cats, due to its potential relationship with conditioned food aversions.

Medications

• Pharmacological therapies targeted at enhancing appetite should not be utilized as a substitute for diagnostic endeavors intended at identifying the specific cause(s) of diminished appetite.
• At the presynaptic level, mirtazapine blocks inhibitory α2‐adrenergic receptors, which makes norepinephrine and serotonin (5-HT) come out more. On the postsynaptic neuron, it blocks both 5-HT2 and 5-HT3 receptors.
• 5-HT1 receptor activation elicits depressive effects, whereas 5-HT2 and 5-HT3 receptor suppression leads to anti-emetic and appetite-stimulating effects.
• The dosage for canines is 0.5 milligrams per kilogram every 24 hours.
• Cats use the FDA-approved medication Mirataz® at a dose of 1.5-inch strip to the inner pinna of the ear once daily for 14 days.
• In cats with chronic kidney illness, an alternative approach to stimulate appetite is to administer 1.88 mg of medication per cat orally every 24 to 48 hours.
• Capromorelin acts as an agonist on the ghrelin receptor, hence inducing appetite centrally within the hypothalamus.
• Entyce®, which refers to capromorelin, has received approval from the FDA for its use as an appetite stimulant in dogs at a dose of 3 mg/kg orally every 24 hours and is considered safe for long-term use.
• Although capromorelin has not yet been approved in cats, a safety trial has been published, and clinical trials are currently being conducted.
• Diazepam, intravenously (0.1 mg/kg every 24 hours).
• Avoid giving oral diazepam to cats due to the potential occurrence of idiosyncratic hepatotoxicosis.
• Cyproheptadine (orally at a dosage of 0.2–0.4 mg/kg, around 10–20 minutes before feeding) to stimulate appetite.
• If ileus is present along with anorexia, prokinetic medications like metoclopramide, ranitidine, or erythromycin may be helpful.
• Anti-emetic medications such as ondansetron and dolasetron reduce the symptoms of nausea or vomiting.
• Maropitant acts as an analogue of substance P by binding to neurokinin-1 receptors located in the chemoreceptor trigger zone (CRTZ) and the vomiting center.
• Cerenia®, also known as maropitant, as an antiemetic (1 mg/kg subcutaneously or intravenously, or 2 mg/kg orally, with a frequency of once every 24 hours in dogs) and (1 mg/kg subcutaneously, intravenously, or orally, once every 24 hours in cats).
• Omega-3 fatty acids decrease inflammatory cytokines, hence exhibiting a minor positive effect on appetite.

Some Notes:

Avoid using antiemetics and prokinetics in cases where there is a presence or suspicion of gastrointestinal obstruction.