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W0117-Section I (31-50).qxd 4/23/04 7:26 PM Page 124 Polyphagia
Ellen N. Behrend
P olyphagia is the consumption of food in excess of and liver disease) lead to polyphagia by unknown mecha- normal caloric intake. Hunger and satiety and, conse- nisms. Secondary polyphagia can also be caused by certain quently, feeding behavior are primarily controlled by certain regions in the central nervous system (CNS), butmany factors affect the function of these areas. Thus polypha-gia can be classified as primary (i.e., a CNS abnormality) or secondary (i.e., a systemic problem affecting the CNS).
Secondary polyphagia is by far more common and usually is Any change in body weight is an important differentiating accompanied by clinical signs of the underlying disease.
feature of the various causes of polyphagia (Figure 34-1).
Determining whether weight gain or loss has occurred should Primary or drug-induced polyphagia typically results in weight be the first step in formulating a list of differential diagnoses gain, because nutrients are adequate and feeding is inappro- priately increased. Pathologic secondary polyphagia is morecommonly associated with weight loss, because the nutrientsupply usually does not meet physiologic demands. However, PHYSIOLOGY
some causes, such as acromegaly, hypoglycemia caused by aninsulinoma, sudden acquired retinal degeneration syndrome Food intake is controlled by a variety of factors, including gas- (SARDS), and hyperadrenocorticism (HAC), lead to weight trointestinal, environmental, and CNS phenomena. The CNS, gain. Physiologic polyphagia can result in weight gain (e.g., mainly the hypothalamus, controls eating behavior. The lateral pregnancy, growth) or maintenance of weight (e.g., lactation, hypothalamic nuclei represent the “feeding center”; their cold environment, increased exercise). An animal with HAC stimulation causes an animal to eat, and their destruction or in the early stages of any of these states, however, may show results in severe, fatal anorexia. Conversely, the ventromedial nuclei are the “satiety center,” because their stimulation causes Certain causes of polyphagia may be diagnosed on the basis a refusal to eat even highly appetizing food, and their ablation of the history. The possibility of exposure to a cold environment, leads to polyphagia and obesity. The feeding center is con- increased exercise and, for intact females, pregnancy and lac- stantly active unless inhibited by the satiety center (e.g., post- tation should be ascertained. Polyphagia is commonly associ- prandially). Lesions of the amygdala or paraventricular nuclei ated with anticonvulsant and glucocorticoid therapy but has been observed with other medications as well (see Table 34-1).
Gastrointestinal components that affect feeding include Psychogenic polyphagia has been noted after introduction of gastric distention, the rate of gastric emptying, the release of a more palatable diet or in response to a stressful event, most gastric hormones, and absorption of nutrients, such as fatty commonly introduction of a new pet into the household.
acids, glucose, and amino acids. The gut hormones can act Feeding of a low-calorie diet may also be diagnosed on the locally on the gastrointestinal tract and centrally on the CNS.
basis of a complete dietary history.
Insulin, glucagon, and cholecystokinin secreted in response to An animal with primary polyphagia caused by destruction a meal decrease feeding signals from the CNS. Leptin, of the satiety center may have a history of trauma or clinical a polypeptide released from adipose tissue, may also help to signs associated with CNS disease. Depending on the extent create a sense of satiety. Decreased serum concentrations of of a hypothalamic lesion, upper motor neuron signs may be glucose, amino acids, or lipid metabolites cause hunger by seen in all four limbs or unilaterally. A midbrain lesion often stimulating neural centers so as to re-establish normal levels.
leads to incessant pacing, circling, and blindness; polyuria/ Feeding behavior also can be incited by increased nutrient polydipsia may also be present. Disorders caused by diffuse or utilization (i.e., an elevated metabolic rate).
multifocal CNS disease will have other clinical signs as well, Normal control of feeding, therefore, is complex and works to maintain energy stores and body weight through an inter- Perturbation of hypothalamic control of the pituitary can play of central and peripheral inputs. Pathologic conditions lead to reproductive, thyroidal, and adrenal hypofunction and that affect the CNS can increase feeding behavior even in associated clinical signs. Hypothyroidism secondary to pitu- the presence of normal energy stores (primary polyphagia). itary dysfunction is clinically identical to primary thyroidal Secondary polyphagia exists when feeding behavior is stimu- failure. If adrenal insufficiency occurs secondary to a lack of lated by non-neural factors and can be caused by an increased adrenocorticotropic hormone (ACTH), vague, nonspecific metabolic rate or decreased nutrient supply (Box 34-1). An signs of lethargy and gastrointestinal disease usually are seen.
augmented metabolic rate can be physiologic (e.g., preg- Serum electrolyte concentrations (e.g., sodium and potassium) nancy) or pathologic (e.g., hyperthyroidism) in origin.
are normal because aldosterone secretion is not affected by Diabetes mellitus is an unusual case of decreased nutrient pituitary disease. This type of hypoadrenocorticism is referred supply. Due to an inability to respond to or a lack of insulin, the body does not recognize glucose and reacts to a perceived Historical findings associated with secondary polypha- hypoglycemia. Certain diseases (e.g., hyperadrenocorticism gia can be highly varied. Animals with diabetes mellitus, W0117-Section I (31-50).qxd 4/23/04 7:26 PM Page 125 acromegaly, HAC, SARDS, and hyperthyroidism usually are Box • 34-1
polyuric and polydipsic. Feline acromegaly is seen in middle-aged to older males, and naturally occurring canine acromegaly Differential Diagnoses of Polyphagia
is seen almost exclusively in intact bitches. In dogs of either AL MANIFEST
sex, progestin administration can lead to acromegaly, and use OF DISEASE
Primary Polyphagia
of this medication should be historically evident. Owners may note inspiratory stridor or a change in body conformation, such as increased interdental spaces, skin folds, or head size inacromegalic animals. It should also be noted that progestin administration to dogs and cats can increase appetite without causing acromegaly. A multitude of historical details can be associated with HAC, including abdominal enlargement, per- sistent panting, failure to regrow hair after clipping, lethargy, and muscle weakness. Animals with SARDS typically havethe presenting complaint of sudden-onset blindness.
Drug-Induced Polyphagia
Hyperthyroidism commonly leads to increased activity but can be associated with depression and lethargy. Gastrointestinal signs (e.g., vomiting and diarrhea) may also be present.
Hypoglycemia has a number of causes. Of these, insulinoma is the most likely to lead to polyphagia, but other neoplasias and insulin overdose may also do so. Hypoglycemic patients may exhibit weakness, trembling, ataxia, disorientation and, possibly, grand mal seizures. Malassimilation can be caused by a number of problems such as pancreatic exocrine insuffi-ciency (PEI), infiltrative bowel disease, parasites, and lymph- Reported Specific Disorders Associated
angiectasia. Malassimilation syndromes and PEI generally with Polyphagia
cause large-volume, malodorous, soft stools. PEI is more common in younger dogs (i.e., those less than 2 years of age), and the German shepherd breed shows a predisposition for this disorder. In older dogs and cats, PEI is rare but, if seen, ismost commonly associated with chronic pancreatitis. The cat- egory of infiltrative disease encompasses processes such asinflammatory bowel disease, neoplasia, and infections such as Secondary Polyphagia
histoplasmosis. Historical details vary according to the under- Acquired esophageal disease often leads to anorexia, but animals with congenital megaesophagus may be polyphagic and typically have a history of regurgitation. Although anorexia is more common in animals with a portacaval shunt, polyphagia has been reported in approximately 10% of cases.
Depression, vomiting, weight loss, polydipsia, and neurologicsigns may also be noted. Polyphagia has been reported rarely in cases of hepatoencephalopathy; other clinical findings are the result of hepatic failure and may be similar to those in an Diabetes mellitusMalassimilation syndromes PHYSICAL EXAMINATION
Physical examination findings in polyphagic animals vary, depending on the underlying disease. With primary polypha- gia, neurologic abnormalities such as ataxia and proprioceptivedeficits may be present. A complete neurologic and fundic examination should be performed. With acute causes of cen- tral blindness, however, the fundus appears normal.
If unclear from the history, pregnancy potentially can be diagnosed by abdominal palpation and lactation by inspection of the mammae. Approximately 80% of cats with hyperthy- roidism have a palpable thyroid nodule, and approximately Sudden acquired retinal degeneration (SARDS) 50% have tachycardia or a gallop rhythm. Hyperthyroidism is rare in dogs, and a cervical mass usually is palpable. Hypera-drenocorticism can have a variety of physical examinationfindings, including abdominal and hepatic enlargement,muscle wasting, bilaterally symmetric alopecia, cutaneoushyperpigmentation, areas of poor hair regrowth or calcinosiscutis. Even when not noted by an owner, the physical changesassociated with acromegaly can be documented on physi-cal examination; a degenerative polyarthropathy may alsobe present.
W0117-Section I (31-50).qxd 4/23/04 7:26 PM Page 126 • Hypoglycemia• Acromegaly• Sudden acquired retinal degeneration syndrome Rule out:• Malassimilation syndromes• Hyperthyroidism• Megaesophagus• Portosystemic shunt• Hepatoencephalopathy Figure 34-1 Algorithm for diagnostic approach to polyphagia.
Examination findings in a dog with SARDS may be unre- DIAGNOSTIC PLAN
markable, because in the early stages of the disease, the reti-nas appear normal on fundic examination. Dogs or cats with The first step in diagnosis is to ascertain what change has PEI, an insulinoma, megaesophagus, hepatoencephalopathy, occurred, if any, in the animal’s weight (see Figure 34-1). After a portasystemic shunt, or a malassimilation syndrome may as many differential diagnoses as possible have been ruled out have no abnormal physical findings other than the associated on the basis of the history, further testing is warranted. In all weight change. In rare cases, polyneuropathies may accom- cases a minimum data base (MDB), including a serum bio- pany an insulinoma. Aspiration pneumonia may be present chemistry profile, complete blood count (CBC), and urinalysis, in animals with megaesophagus. Neurologic abnormalities may be detected in an animal with a portasystemic shunt, For dogs and cats with weight gain, pregnancy must be and ascites is noted in approximately 20% of afflicted dogs.
ruled out. To diagnose primary polyphagia, a complete neuro- Neurologic findings associated with hepatoencephalopathy logic examination should be performed, any abnormalities may be episodic, and other examination findings vary with the localized, and appropriate tests obtained. A cerebrospinal fluid cause of liver disease. Depending on the cause of malassimila- analysis or diagnostic imaging, such as radiography, computed tion, the intestines may feel thickened. Lymphangiectasia may tomography (CT), or magnetic resonance imaging (MRI), may Occasionally, polyphagia may be a clinical sign of a disease Hypoglycemia caused by an insulinoma usually can be diag- with which it is not usually associated. For example, one cat nosed by measuring paired blood glucose and insulin serum with feline infectious peritonitis (FIP), one with foreign body concentrations when the animal is hypoglycemic. Rarely, encephalitis, and one with spongiform encephalopathy have provocative testing may be required (see Chapter 240). The been reported as being polyphagic, as have 18 cats in diagnosis of SARDS can be made on the basis of appropriate Great Britain with lymphocytic cholangitis. Other historical history, physical examination findings, an MDB that rules out and clinical signs are present depending on the cause.
other causes and, if necessary, an electroretinogram (ERG).
W0117-Section I (31-50).qxd 4/23/04 7:26 PM Page 127 Although certain changes in the MDB are typical of hyper- of the cause. Determination of preprandial and postprandial adrenocorticism, they do not confirm the diagnosis and fur- serum bile acid concentrations can document hepatic dys- ther adrenal testing must be performed; an ACTH stimulation function, but a biopsy may be required to document the cause test or low-dose dexamethasone suppression test should be of hepatic failure. Ultrasonography or a radionuclide scan may AL MANIFEST
performed to confirm the diagnosis (see Chapter 242).
be used to identify a portacaval shunt.
OF DISEASE
Diagnosis of acromegaly can be difficult because of the lack of If the disease is in the early stages, weight change may not a commercial assay for growth hormone, but measurement of yet have occurred, and the list of differentials may be difficult insulin-like growth factor-I (IGF-I) may be helpful (see to narrow. However, a good history and physical examination Chapter 235). The history, together with conformational combined with an MDB can eliminate many possibilities.
changes, can provide evidence of the underlying disease.
Although animals with HAC may not have a weight change, Acromegalic cats consistently have insulin-resistant diabetes abdominal enlargement may create the impression of weight mellitus, and imaging of the pituitary may reveal a tumor.
gain. All diseases suspected as possible differential diagnoses If weight loss is associated with polyphagia, the MDB in this situation should be diagnosed as discussed above.
should be preceded by three fecal examinations. If the resultsof these are negative, the MDB does not provide the diagno-sis, and the animal is stable, trial therapy with antiparasiticides MANAGEMENT
may be warranted. If deworming does not resolve the prob-lem, additional tests must be done. Hyperthyroidism often The management of polyphagia depends on the cause.
can be diagnosed on the basis of a single serum thyroxine Physiologic causes of polyphagia are transient. If the condi- measurement; however, other tests, such as measurement of tion is drug induced, the polyphagia may be temporary, as is the free thyroxine concentration by equilibrium dialysis, may usually seen with anticonvulsants. Psychogenic polyphagia may be corrected by removing the instigating element, if Malassimilation syndromes cover myriad differential diag- possible, or by behavioral therapy (e.g., paying more attention noses (see Table 34-1). Protein-losing enteropathies can be to the animal). If the polyphagia persists with ongoing drug associated with hypoalbuminemia and hypoglobulinemia.
therapy or if the inciting agent (stress or medication) cannot Depending on the suspected cause, measurement of serum be removed, food intake should be limited to that necessary folate or cobalamin, assessment of fat absorption, abdominal to satisfy caloric requirements. Low-calorie, high-fiber foods, radiography or ultrasonography, and/or biopsy either by such as carrots, can be added to the diet to assuage hunger endoscopy or exploratory surgery may also be considerations.
and prevent obesity. Polyphagia caused by dietary factors For verification of PEI, serum trypsin-like immunoreactivity can be managed as needed. In cases of SARDS, the poly- (TLI) should be determined. Thoracic radiographs with phagia usually is self-limiting. For all other conditions, appro- a positive contrast esophagram should be used to diagnose priate therapy should be initiated to resolve the underlying megaesophagus; this imaging may also aid in the determination Ptyalism
Sandra Manfra Marretta
P tyalism is the excessive production and secretion the pharynx,esophagus,and stomach also may stimulate the of saliva. Pseudoptyalism is the drooling or dribbling of production of excessive amounts of saliva. In some cases saliva because of an inability or reluctance to swallow, this excess may be clinically evident not as drooling but as which results in an overflow of saliva from the oral cavity.
Anatomic abnormalities of the oral cavity may cause saliva to drip from the mouth even when normal amounts of saliva PATHOPHYSIOLOGY
are produced. Drooling is evident with diseases in which the animal is unable or reluctant to swallow because of pain Saliva is continuously produced by the salivary glands. The production of saliva may be increased by excitation of the salivary nuclei, located in the brain stem, after taste andtactile stimuli are received from the tongue and other areas in HISTORICAL FINDINGS AND THEIR MEANINGS
the oral cavity. Higher centers in the central nervous system(CNS) may also have an excitatory or inhibitory affect on the Age and Breed
salivary nuclei. Increased production of saliva is a normal Young animals with congenital anomalies, including porto- physiologic occurrence associated with imminent feeding, systemic shunt and megaesophagus, may hypersalivate. Jaw abnormalities, such as severe retrognathism, may cause Oral lesions and central nervous system disorders may excessive drooling. In some giant breed dogs, the shape and size stimulate an increase in the production of saliva. Diseases of of the lower lip may predispose to drooling. Young animals are

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