Polyphagia
Polyphagia in dogs is the medical term used for excessive appetite or overeating. A dog with polyphagia has an abnormal and ravenous appetite.
PATHOPHYSIOLOGY
Failure to assimilate or loss of nutrients (e.g., maldigestion/malabsorption syndromes such as exocrine pancreatic insufficiency).
Inability to use nutrients (e.g., diabetes mellitus, poor-quality diets, gastrointestinal parasites).
Hypoglycemia (e.g., insulinoma, insulin overdose).
Increased metabolic rate or demand (e.g., hyperthyroidism, cold environments, pregnancy, lactation).
Psychologic or learned behaviors (e.g., palatable diets, competition, drugs such as anticonvulsants or glucocorticoids).
SYSTEMS AFFECTED
Cardiovascular—obesity can worsen the clinical cardiac disease.
Central nervous system—tumors of the brain, especially of the hypothalamus, can cause polyphagia.
Integument—obese animals, especially cats, are susceptible to dermatitis.
Musculoskeletal—Overweighted patients are susceptible to arthritis and other orthopedic problems.
Respiratory—obesity exacerbates dyspnea in patients with respiratory disease.
SIGNALMENT
Dogs and cats
SIGNS
Historical Findings
Eating more frequently and/or a greater quantity than normal.
Excessive food-seeking and food-stealing behaviors are possible.
Weight loss may occur with certain disease states (e.g., exocrine pancreatic insufficiency, diabetes mellitus, hyperthyroidism).
PU/PD occurs in some patients (diabetes mellitus, hyperthyroidism, hyperadrenocorticism).
Physical Examination Findings
Patients may have excessive body fat, but those with an underlying medical problem (e.g., exocrine pancreatic insufficiency, diabetes mellitus, hyperthyroidism) may be thin.
CAUSES & RISK FACTORS
Physiologic
Pregnancy
Lactation
Growth
Response to a cold environment
Increased exercise
Pathologic
Diabetes mellitus
Hyperthyroidism—cats
Hyperadrenocorticism—dogs
Exocrine pancreatic insufficiency
Gastrointestinal parasites
Insulinoma
Insulin overdose
Lymphangiectasia
Growth hormone-secreting pituitary tumor
Megaesophagus
Lymphocytic plasmacytic enteritis—cats—uncommon
Neoplasms of the brain—rare
Gastrointestinal neoplasms—rare
Iatrogenic
Corticosteroids
Progestins
Benzodiazepines
Anticonvulsants
Palatable food/overfeeding
Poor diet
Competition for food
DIAGNOSIS
DIFFERENTIAL DIAGNOSIS
PU/PD (excessive trips to food/water area)—differentiated by observation.
CBC/BIOCHEMISTRY/URINALYSIS
Neutrophilia, monocytosis, lymphopenia, and eosinopenia with hyperadrenocorticism, and in patients receiving corticosteroids.
Hyperglycemia with diabetes mellitus, growth hormone-secreting pituitary tumors (cats, insulin-resistant diabetes mellitus), and hyperadrenocorticism (mild).
Hypercholesterolemia with recent food intake, hyperadrenocorticism, and diabetes mellitus, and in patients receiving corticosteroids.
High ALP and ALT activity with hyperadrenocorticism (dogs), hyperthyroidism (cats), and diabetes mellitus, and in patients receiving corticosteroids.
Hypoproteinemia with protein-losing enteropathies (e.g., lymphangiectasia, inflammatory bowel disease).
Hypoglycemia in patients with insulinoma or insulin overdose.
Low urine specific gravity with diabetes mellitus, diabetes insipidus, hyperthyroidism, and hyperadrenocorticism, and in patients receiving corticosteroids.
Glucosuria, possibly ketonuria, with diabetes mellitus.
OTHER LABORATORY TESTS
Fecal examination to rule out gastrointestinal parasites.
Serum trypsin-like immunoreactivity to diagnose exocrine pancreatic insufficiency.
Total serum T4 to rule out hyperthyroidism (cats); T3 suppression testing if hyperthyroidism is suspected but serum total T4 is normal.
Low-dose dexamethasone suppression or ACTH stimulation test to diagnose hyperadrenocorticism; plasma ACTH level or high-dose dexamethasone suppression testing to differentiate pituitary-dependent hyperadrenocorticism from adrenal tumor if hyperadrenocorticism is confirmed with the low-dose dexamethasone suppression test or ACTH stimulation test.
Serum insulin levels in hypoglycemic patients to rule out insulinoma.
IMAGING
Abdominal radiology may demonstrate hepatomegaly associated with hyperadrenocorticism, diabetes mellitus, and corticosteroid administration.
Abdominal ultrasonography may demonstrate an adrenal mass or bilateral adrenomegaly (hyperadrenocorticism), hepatomegaly (hyperadrenocorticism, diabetes mellitus, and corticosteroid administration), bowel wall thickening or bowel wall layering disruption (inflammatory bowel disease, lymphoma, lymphangiectasia), and pancreatic masses (insulinoma).
Magnetic resonance imaging could be used to visualize a neoplasm of the hypothalamus.
DIAGNOSTIC PROCEDURES
Endoscopy with biopsy of the upper gastrointestinal tract to rule out gastrointestinal diseases.
TREATMENT
Usually outpatient medical management.
Polyphagia without weight gain or with weight loss is more likely due to a medical problem; evaluate the animal prior to food restriction or manipulation.
Once pathologic causes of polyphagia have been excluded, limit the amount of food available, feed a reduced-calorie diet, and/or increase exercise if obesity or weight gain is present.
Owners must measure food to accurately assess intake.
Some dogs may benefit from the addition of low-calorie bulky foods such as canned green beans.
Feeding smaller meals two to three times daily may be beneficial for some patients, provided the total food provided remains the same as required by life stage and activity to promote weight loss or prevent weight gain.
Removing the pet during human meal preparation and consumption to reduce begging behavior and the pet obtaining additional food.
Slowing down the rate of eating may be beneficial in some dogs, using food-dispensing toys that require manipulation to obtain daily ration.
If social issues within the home influence intake these must be addressed:
Feed all dogs in separate locations, preferably without visual contact.
Have multiple feeding stations available in a multiple-cat home.
The average animal’s daily caloric need can be estimated by the formula 30 × weight (kg) + 70.
Chew toys can be used as a substitute for food.
MEDICATIONS
DRUG(S)
See specific diseases for detailed therapy.
Drug-induced—attempt to taper or discontinue the drug.
If a compulsive eating disorder is suspected in dogs, clomipramine (1–3 mg/kg PO q12h) or fluoxetine 1–2 mg/kg q24h may be used or in cats clomipramine 0.25–1.0 mg/kg q24h or fluoxetine 0.5–1.0 mg/kg q24h.
Dirlotapide is a selective microsomal triglyceride transfer protein inhibitor that blocks the assembly and release of lipoprotein chylomicrons into the bloodstream, thus triggering peptide YY release and a decreased appetite. This could be used in obese dogs at a dose of 0.01–0.02 mL/kg PO q24h (see package insert for dose adjustment protocol).
FOLLOW-UP
PATIENT MONITORING
Monitor body weight in patients with non-pathologic causes of polyphagia.
Assess compliance with feeding regime and food measurement to decrease intake and promote weight loss.
POSSIBLE COMPLICATIONS
Obesity in non-pathologic polyphagia.
The owner responds to begging behavior and caloric intake is not decreased.
Weight loss/emaciation in pathologic causes of polyphagia.
Worsening of respiratory or cardiovascular disease processes in obese patients.
MISCELLANEOUS
ASSOCIATED CONDITIONS
Obesity
PREGNANCY/FERTILITY/BREEDING
A normal physiologic response to pregnancy.
SYNONYMS
Eating disorder
Hyperphagia