From Young MS: Aggressive behavior. In Ford RB, editor: Clinical signs and diagnosis in small animal practice, New York, 1988, Churchill Livingstone.

^* These behavior patterns are not pathologic states. They are typical patterns of the species and are therefore normal. Familiarity with the normal, species-typical aggressive pattern of the dog enables differentiation of species-typical patterns from pathophysiologically based aggression. As with many animal behavior problems, species typicality does not lessen the problem’s disruptiveness or danger.

Diagnostic plans

1. Laboratory profile and neurologic examination to assess the presence of pain or underlying organic disease (intracranial disease).

2. Note: Administration of a psychotropic drug as empiric therapy for aggression is not recommended before determining a possible cause and attempting to modify behavior through training.

Aggressive Behavior in the Cat: Differential Diagnosis According to Origin

Pathophysiologically Based Aggressive Behavior

Rabies

Intracranial neoplasia and lesions

Species-Typical Aggressive Behavior *

Intermale aggression

Predatory aggression

Play aggression

Territorial aggression

Fear-induced aggression

Pain-induced aggression

Maternal aggression

Redirected aggression

^* These behavior patterns are not necessarily caused by pathologic states. They are characteristic behavior patterns of the species and therefore can be normal. Familiarity with the normal, species-typical aggressive patterns of the cat enables differentiation of species-typical patterns from pathophysiologically based aggression. As with many animal behavior problems, species typicality does not lessen the problem’s disruptiveness or danger.

Alopecia

See Hair Loss: Alopecia.

Ataxia

See Incoordination: Ataxia.

Blindness

See Vision Loss: Total Blindness.

Blood in urine: hematuria, hemoglobinuria, myoglobinuria

Definition

Hematuria is the presence of blood in the urine; the presence of trace amounts of blood in the urine will not be obvious on gross appearance of a urine sample. Therefore any noticeable change in the color of urine observed by the owner is likely to be interpreted as “blood in the urine.” Further evaluation of the patient is necessary to determine whether or not the discoloration is associated with small blood clots in recently voided urine, blood-tinged urine, or brown or red urine. The presence of blood in the urine, whether gross or occult, is most often indicative of upper or lower urinary tract bleeding, although systemic coagulopathies and reproductive tract disorders may also cause hematuria. The presence of hemoglobin in urine (hemoglobinuria) is not necessarily a reflection of urinary tract disease. Systemic disorders (e.g., those leading to intravascular hemolysis) can be associated with significant hemoglobinuria in the presence of a normal urinary system. Owners are likely to interpret this clinical sign to be “blood in the urine.” In true hemoglobinuria, without hematuria, microscopic examination will reveal the absence of red blood cells (RBCs).

Distinguishing hemoglobinuria from hematuria is an important diagnostic consideration. Conventional urine test strips (dipsticks) do not differentiate between the two; therefore microscopic examination of urine sediment for the presence of significant numbers of RBCs is critical.

Myoglobinuria is characterized by brown to dark-red urine, the absence of RBCs in the urine sediment, and a positive finding on testing for occult blood. Bilirubinuria can also cause dark-brown to dark-orange urine but alone will not produce a test result positive for occult blood. Myoglobinuria is a serious sign and denotes generalized muscle disease.

Associated signs

Hematuria associated with the urinary tract may not be associated with any other clinical signs. In patients with significant bleeding of renal origin, evidence of systemic illness may be present but is unlikely to localize the source of hematuria. Hematuria originating from the bladder is more likely to be associated with clinical signs, particularly pollakiuria and dysuria. Reproductive tract disorders (e.g., prostatitis and vaginitis) can also cause significant hematuria. Patients with hematuria or hemoglobinuria should be examined carefully for evidence of systemic bleeding, coagulopathies, and neoplasia.

Differential diagnosis

Diagnostic plans

1. Thorough history and physical examination, with emphasis on examination of the genitalia, palpation of the prostate, and caudal abdominal palpation.

2. If practical, assessment of urethral patency and the patient’s ability to urinate. Attempt to pass a urethral catheter if significant dysuria and evidence of lower urinary tract obstructions are present.

Causes of Apparent or Actual Hematuria in Dogs and Cats Classified by Anatomic Site of Origin

Site	Diseases
Kidney	Pyelonephritis Glomerulonephropathy or glomerulonephritis Neoplasia Calculi Renal cysts Renal infarction
	Renal trauma Benign renal bleeding Hematuria of Welsh Corgis Dioctophyma renale infection Microfilaria of Dirofilaria immitis Chronic passive congestion
Bladder, ureter, urethra	Infection, inflammation, cystitis, LUTD Cystic calculi Neoplasia Trauma Thrombocytopenia Capillaria plica infection Cyclophosphamide therapy
Any site	Coagulopathy Heat stroke DIC
Extraurinary sources (genital tract or spurious hematuria)	Prostate Neoplasia Infection Hypertrophy Uterus, pyometra Estrus Subinvolution Infection Neoplasia (including TVT) Vagina Trauma Penis TVT

DIC, Disseminated intravascular coagulation; LUTD, lower urinary tract disease; TVT, transmissible venereal tumor.

3. Complete urinalysis. Using a fresh sample, include assessment of gross appearance, specific gravity, biochemical reagent strips (dipsticks), and microscopic examination of urine sediment. Ideally, two samples should be collected: a voided urine sample followed by a urine sample collected by cystocentesis.

4. Culture and sensitivity, if bacteria are present.

5. Routine laboratory profile, to include hematology and biochemistry panel.

6. Coagulation profile, if hemoglobinuria is present.

7. Abdominal radiographs, for evidence of calculi, prostatic enlargement, and soft tissue masses.

8. Contrast radiography of the upper and lower urinary tracts.

9. Ultrasound examination of the prostate, urinary bladder, and kidneys.

10. Exploratory laparotomy (if coagulation profile is normal).

Coma: loss of consciousness

Definition

Coma is a state of complete reversible or irreversible unconsciousness that can result from neurologic as well as nonneurologic disease (drug overdose, especially in dogs). Coma can be a consequence of diffuse or multifocal lesions of the cerebrum or a lesion affecting the rostral brainstem and ascending reticular activating system. A variety of organic central nervous system (CNS) diseases leading to metabolic or toxic encephalopathy can also produce coma.

Associated signs

Despite the fact that the comatose patient is unconscious, a complete neuroophthalmologic examination should be completed. Altered pupil size and pupillary light responses usually indicate brainstem disease. Emergency cardiac assessment of the unconscious patient justifies an electrocardiogram (ECG) and thoracic radiographs. Laboratory assessment of the comatose patient includes hepatic enzymes and, when feasible, hepatic function, electrolytes, and glucose level.

Differential diagnosis

Differential Diagnosis of Coma

	Neurogenic	Nonneurogenic
Acute, nonprogressive	Intracranial hemorrhage Brain malformations	— —
Acute, progressive	Metastatic lesions Epidural, subdural hemorrhage Meningoencephalitis Cerebral edema	Hypoglycemia Diabetic coma (hyperosmotic) Heat stroke Hepatic or uremic encephalopathy Infection Hypoxia Thiamine deficiency (cat) Heavy metal and drug toxicity Carbon monoxide poisoning
Chronic, progressive	Hemorrhage (rare) Storage diseases Hydrocephalus Encephalitis	Heavy metal toxicity

Diagnostic plans

1. Critical: Assessment of vital signs to evaluate airway, breathing, and circulation (pulse, heartbeat, and ECG). Take thoracic radiographs if indicated. If cerebral edema is suspected, administer ventilation support, intravenous hyperosmotic agents (e.g., mannitol 20%, 1 to 2 g/kg of body weight q6h), and glucocorticoids.

2. Conduct careful neurologic examination directed toward evaluation of brainstem function, including motor function, pupillary light responses (or lack thereof), and eye movement.

3. Comprehensive laboratory profile, to include hematology, biochemical profile, and urinalysis.

4. Special diagnostic tests as appropriate:

a. Metabolic coma: Serum ammonia, bile acids, glucose, blood and urine lead levels

b. Neurologic coma: Skull radiographs, cerebral spinal fluid analysis, electroencephalography

c. Assessment of response to intravenous mannitol.

Constipation (obstipation)

Definition

Constipation is the infrequent or difficult passage of feces. Obstipation is intractable constipation resulting in fecal impaction through the rectum and possibly the colon. The act of straining to defecate or painful defecation, the likely manifestation of constipation or obstipation, typically represents the reason for which a constipated dog or cat is presented (see also Straining to Defecate: Dyschezia).

There is no strict definition of bowel regularity; therefore there is no “normal” number of daily or weekly bowel movements, deviations from which constitutes constipation. Practically, constipation can be considered to exist when a significant delay in frequency of passing formed stools has been noted or when the stool is observed to be of unusually hard or dry consistency. Constipation is categorized under one of the following headings: neurogenic; mechanical (physical); muscular (smooth muscle); or iatrogenic (drug-induced).

The owner who perceives a pet as straining to defecate may, in fact, be observing a pet that is straining to urinate. This is particularly true in cats with disorders of the lower urinary tract, such as feline urologic syndrome (FUS). In the context of this discussion, dyschezia is discussed only insofar as it is associated with constipation and obstipation (Figure 3-2).

Figure 3-2: Clinical algorithm for constipation in the dog or cat. EMG, Electromyogram.

Associated signs

Assessment of the patient presented because of constipation or obstipation can represent a significant medical challenge because of the complex and varied pathogenic mechanisms involved. Animals with neurogenic causes of constipation may have significant perianal or rectal pain associated with focal lesions. Other patients may have nonpainful neurologic disease or long-term complications stemming from previous pelvic or spinal trauma.

Mechanical causes are either extraluminal or intraluminal. Abdominal and rectal palpation is indicated in both male and female dogs and cats. Narrow or blood-tinged feces may signal the presence of an intraluminal lesion, whereas in patients with extraluminal lesions, associated clinical signs may not be present.

Muscular causes are the least common and are generally the result of extreme metabolic aberrations. Idiopathic colonic atony is reported, but constipation may also result from severe catabolic states. Laboratory evidence of endocrine disease and electrolyte abnormalities should be assessed.

Differential diagnosis

Diagnostic plans See Figure 3-2.

Differential Diagnosis of Constipation

Neurogenic causes

Cortical (pain-induced constipation)

Central nervous system disease

Spinal trauma

Spinal neoplasia

Degenerative myelopathy

Peripheral nerve disease (e.g., complication after pelvic trauma)

Mechanical Causes

Extraluminal

Prostate (neoplasia or hyperplasia)

Large intraabdominal tumors

Pregnancy (?)

Pelvic fracture

Intraluminal

Rectal stricture (e.g., adenocarcinoma)

Colonic stricture

Granulomas (e.g., histoplasmosis)

Benign colorectal tumors

Fecalith

Rectal-colonic prolapse

Intussusception

Muscular causes

Colonic atony

Severe malnutrition and cachexia

Segmental dilation subsequent to surgery

Drug-Induced Causes

Anesthetics

Anticholinergics (e.g., atropine)

Anticonvulsants

Barium sulfate

Diuretics

Prolonged laxative therapy

Monoamine oxidase inhibitors

Heavy metal toxicity (e.g., lead)

Behavioral factors

Soiled or odiferous litter

No litter available

Cough

Definition

A cough is a sudden, forceful expiratory response to irritating stimuli (e.g., secretions) situated in the tracheobronchial tree. Cough is the most frequent clinical presentation (followed by dyspnea and hemoptysis) that is referrable to the lower respiratory tract. At presentation, cough should be characterized as “acute-onset” (duration of only a few days) or “chronic” (duration longer than 2 weeks). Attempting to characterize cough as productive or nonproductive is difficult in animals and therefore has little value in the overall diagnostic plan.

Associated signs

Although cough is a principal sign of lower respiratory tract disease, particularly lower airway (tracheal and bronchial) disease, it may also occur in animals with nonpulmonary disease, particularly cardiac and intrathoracic diseases. Associated signs, therefore, may include a wide spectrum of findings; there may also be no associated signs. Particular attention should be given to determining the character of the cough: it can be paroxysmal and severe, which usually indicates the need for immediate intervention, or mild but persistent. Animals in need of immediate attention are those with cough associated with syncope, dyspnea, or hemoptysis. Orthopnea, the inability to breathe without assuming a particular (usually upright) position, is a serious sign that suggests compromised respiratory function and also warrants immediate attention. Nasal discharge, tachypnea, and hyperpnea are less commonly associated with cough. Cough can be misinterpreted by the owner as vomiting, particularly in dogs with infectious airway disease.

Differential Diagnosis of Cough

Primary Respiratory Tract Disease

Canine infectious respiratory disease (CIRD; formerly “kennel cough”); multiple viruses and bacteria may be involved

Tonsillitis and pharyngitis

Tonsillar neoplasm

Pharyngeal polyp (cat)

Laryngeal cyst

Laryngeal neoplasm

Laryngeal paralysis

Tracheal hypoplasia (usually with secondary tracheitis)

Segmental tracheal stenosis

Tracheal collapse—acquired and congenital

Tracheal neoplasia

Tracheal osteochondral dysplasia

Foreign body

Bronchiectasis

Bronchial collapse

Immotile cilia syndrome

Aspiration

Respiratory parasites (e.g., Capillaria aerophila in cats; Filaroides osleri in dogs)

Pulmonary Vascular Disease

Pulmonary edema (multiple causes)

Pulmonary hypertension, especially heartworm disease

Pulmonary Parenchymal Disease

Bacterial pneumonia

Systemic mycoses (e.g., histoplasmosis)

Pulmonary neoplasia

Pulmonary abscess

Protozoan pneumonia (e.g., feline toxoplasmosis)

Viral pneumonia

Allergic pneumonitis (e.g., feline asthma)

Metabolic and endocrine disease (e.g., hyperadrenocorticism)

Cardiovascular Disease

Left-sided heart disease

Left-sided heart failure (cardiogenic pulmonary edema)

Intrathoracic Disease

Mediastinal abscess

Mediastinal neoplasia

Differential diagnosis

Diagnostic plans

1. History and physical examination. Focus on recent exposure risk (boarding) and heartworm preventative in dogs. Physical examination is particularly valuable in determining the extent of respiratory tract involvement and characterizing the type of cough present, particularly when the cough can be elicited by manipulation of the cervical trachea.

2. Careful thoracic auscultation to determine the presence or absence of heart murmur or abnormal lung or airway sounds.

3. Thoracic radiographs using lateral and ventrodorsal projections are critical, particularly when the patient has associated signs compatible with respiratory distress. Oxygen should be available to the dyspneic patient throughout the radiographic procedure. Radiographs should be carefully reviewed for changes in vascular, cardiac, and airway patterns. Patients suspected of having thoracic neoplasia should have left and right lateral thoracic radiographs assessed.

4. A laboratory profile, to include hematology, biochemistry panel, fecal flotation, urinalysis, heartworm test, and feline leukemia virus and feline immunodeficiency virus (FeLV/FIV) test in the cat.

5. Special diagnostics:

a. Primary respiratory disease: transtracheal aspiration, bronchial lavage, bronchoscopy, contrast bronchography, fluoroscopy, and radionuclide assessment of mucociliary transport

b. Primary pulmonary disease: fine-needle lung aspiration, arterial blood gases, fungal serology, nuclear studies (perfusion-ventilation), lung biopsy

c. Primary cardiac disease: ECG, echocardiogram (M-mode and two-dimensional), and nonselective angiography

Coughing blood: hemoptysis

Definition

Hemoptysis is the expectoration, during cough, of blood. Seldom is the volume of blood loss sufficient to cause anemia; however, once confirmed, hemoptysis is a severe clinical finding indicative of bleeding into or from the lower airways. Hemoptysis can be attributed to direct injury of the pulmonary or, less commonly, the tracheobronchial blood vessels; pulmonary hypertension; or coagulopathy. Although an uncommon presenting sign, hemoptysis is more prevalent in dogs than in cats.

Because vomiting can be mistaken by the owner for coughing, it becomes essential to differentiate between hemoptysis and hematemesis during the initial examination. Hemoptysis is regarded as an emergency presentation.

Associated signs

The most common, and least significant, sign associated with hemoptysis is melena, or dark-red or black discoloration of stool that occurs subsequent to swallowing expectorated blood. More serious associated signs include coughing, hyperpnea, orthopnea, and cyanosis. Apparent episodic weakness and collapse may also be reported.

Differential diagnosis

Differential Diagnosis of Hemoptysis

Cardiovascular Hemoptysis

Thromboembolic disease

Heartworm disease (in the dog and cat)

Hyperadrenocorticism

Cardiomyopathy

Renal amyloidosis (in the dog)

Idiopathic hemoptysis

Acute pulmonary edema

Arteriovenous fistula

Parasitic Hemoptysis

Lung flukes (e.g., Paragonimus species)

Lungworms (e.g., Aelurostrongylus species)

Inflammation-Induced Hemoptysis

Chronic bronchitis

Pneumonia

Mycotic lung infection

Lung abscess

Neoplasia

Either primary or metastatic neoplasia

Miscellaneous

Coagulation disorder

Direct injury or trauma

Transtracheal aspiration (for diagnostic sampling)

Diagnostic plans

1. Thorough history and physical examination. In addition, an attempt should be made to determine that the sign for which the patient was presented is, in fact, expectoration of blood during coughing and not bloody vomitus.

2. Routine laboratory profile, to assess the patient’s overall health status. Emphasis should be placed on the fecal examination and heartworm tests. Multiple attempts to locate parasite ova in the stool should be made, because lung parasites may be few in number and ova shed intermittently.

3. Thoracic radiographs (especially for evidence of advanced heartworm disease in dogs).

4. Coagulation profile, particularly in those animals with significant bleeding from other sites.

5. Transtracheal aspiration with cytologic studies or bacterial culture and sensitivity tests, or both.

6. Special procedures, including ultrasonography of the lung, particularly when discrete masses are seen on radiographs; echocardiography; blood gas analysis; bronchoscopy; bronchography; and angiography.

7. Radionuclide scans. Although availability is limited, studies may detect areas of pulmonary embolization.

Deafness or hearing loss

Definition

Deafness is the detectable lack or loss (complete or partial) of the sense of hearing. Deafness can result from abnormalities at any one of several levels from the ear to the brain. Peripheral deafness is categorized as either conduction deafness, involving abnormalities of the transduction apparatus (external ear canal, tympanic membrane, auditory ossicles in the middle ear), or nerve deafness, involving the hearing receptors in the cochlea or the auditory branch of the eighth cranial nerve. Congenital deafness is usually nerve deafness and is the result of abnormal development of the middle and/or inner ear. Central hearing loss (intracranial cause) is uncommon.

Loss of hearing, either complete or partial, in one or both ears does occur in both dogs and cats but is particularly difficult to confirm. Partial loss of hearing occurs most commonly in older animals and is noted by owners as decreased response to voice or noise (e.g., thunder).

Associated signs

Although rare, invasive lesions or panencephalitis could conceivably cause central hearing loss. However, the associated neurologic signs would be extensive, and hearing loss becomes a secondary or insignificant clinical issue.

Animals with peripheral hearing loss caused by acquired unilateral lesions (severe otitis externa) may manifest a variety of signs referable to the inner ear, particularly head tilt and, less often, circling. Pain or increased sensitivity may be associated with infectious lesions affecting hearing in either ear. Physical evidence of otitis externa is readily detected during routine examinations. Severe swelling associated with a chronic inflammation, a ruptured or damaged tympanic membrane, and infections of the middle ear may effectively decrease hearing acuity. Hypothyroidism may also be associated with degeneration of the cochlea and subsequent decrease in hearing acuity. The clinical history is important and should include any prior exposure to drugs known to be toxic to the cochlear nerve and organ of Corti (e.g., aminoglycoside therapy).

Congenital (hereditary) deafness is associated with a white or merle hair coat in both dogs and cats. In dogs, the highest incidence occurs in the Dalmatian. However, several breeds are reported to be affected.

Differential diagnosis

Differential Diagnosis of Deafness

Acquired Hearing Loss

Degenerative causes

Neurogenic deafness in the geriatric dog and cat

Hearing loss occurring subsequent to chronic inflammatory disease (middle and inner ear structures)

Metabolic (endocrine) cause

Hypothyroidism

Neoplastic cause

Invasive tumors of the pharynx and retropharyngeal tissue

Infectious-inflammatory causes

Otitis (externa, media, and/or interna)

Canine distemper virus infection

Protothecosis (in the dog)

Toxic cause

Aminoglycoside antimicrobials, especially gentamicin, streptomycin, and neomycin

Traumatic hearing loss

Idiopathic hearing loss

Congenital Hearing Loss—Breed Predisposition

White, blue-eyed cats (may be unilateral or bilateral)

Several breeds affected, particularly those with a white or merle hair coat

Diagnostic plans

1. Assessment of response to noise while the animal is relaxed or asleep.

2. Thorough physical examination, particularly of the external ear canal and tympanic membrane.

3. Otoscopic or videoscopic examination in the anesthetized patient.

4. Neurologic examination.

5. Assessment of thyroid hormone levels.

6. Radiography or computed tomography (CT) of the head, with particular emphasis on the tympanic bullae, for evidence of otitis media.

7. Electrophysiologic studies, including electroencephalography, tympanometry, and brainstem auditory evoked potentials (BAER test).

Decreased urine production: oliguria and anuria

Definition

Oliguria is a reduced amount of urine production and output in relation to fluid intake. Patients in which urine production ceases have anuria and are considered to be anuric. In contrast to polyuric states, neither oliguria nor anuria is likely to be the primary problem for which a dog or cat is presented. The metabolic consequences of decreased urine production are severe and generally represent significant compromises in renal blood flow or in the functional status of a critical nephron mass. The daily urine volume at which oliguria begin is a function of solute load and renal concentrating ability. In general, oliguria exists when daily urine production is reduced by 75% or more. Production of 0.5 to 1.0 mL of urine per kilogram per hour indicates adequate renal perfusion in the dog. Anuria begins or terminates with oliguria; therefore early detection and treatment of the underlying cause are critical to the overall prognosis.

Associated signs

The problem(s) for which an oliguric or anuric patient is presented will likely be related to the metabolic consequences of compromised renal function. Uremia, characterized by vomiting, hematemesis, diarrhea, lethargy, or anorexia, predominates. Any one or a combination of signs may present at the time of initial examination. Some patients may be presented in a comatose or semiconscious state, in which case it is essential that renal function and urinary output be established immediately.

Because acute renal failure (ARF) is the principal differential diagnosis in oliguria and anuria, once it has been established the clinician must obtain a thorough clinical history and laboratory profile, including urinalysis if possible, in an attempt to determine the cause of renal failure and to institute corrective therapy.

Differential diagnosis

Differential Diagnosis of Acute Renal Failure

Inflammatory-Infectious Causes

Leptospirosis

Pyelonephritis

Immune complex glomerulonephropathy

Systemic lupus erythematosus

Heartworm disease

Pyometra

Endocarditis

Feline leukemia virus infection

Lyme borreliosis (uncommon outside of endemic areas)

Viral causes

Canine distemper virus infection

Infectious canine hepatitis infection (rare in the United States)

Canine herpesvirus infection (rare)

Primary Renal Causes (Nephroses)

Hypoperfusion (ischemia)

Thromboembolic diseases

Nephrotoxins

Heavy metals (lead, arsenic, thallium, mercury)

Carbon tetrachloride

Ethylene glycol (antifreeze)

Aminoglycoside antibacterials (amikacin, gentamicin)

Antibiotics (cephaloridine, amphotericin B)

Hypercalcemia

Anesthetics (adverse reaction—rare)

Diagnostic plans

1. Initiation of fluid therapy and placement of an indwelling urinary catheter, to establish the rate of urine production.

2. History, to address any possible exposure to toxins, particularly antifreeze, as well as recent drug treatment.

3. Radiographs of the abdomen. These may reveal enlarged kidneys, thereby supporting a diagnosis of ARF. Do not rule out the diagnosis of ARF if kidney size appears normal. Ultrasound imaging of kidneys is also helpful in establishing diagnosis.

4. Complete blood count (CBC). The biochemical profile should include electrolytes as well as blood urea nitrogen (BUN) and creatinine levels. Urinalysis (must include urine specific gravity) with microscopic examination of sediment for evidence of crystalluria, RBCs, white blood cells (WBCs), and casts is essential even if only a small volume of urine can be obtained.

5. Blood gases, to assess for metabolic acidosis, which may be severe in ARF.

6. Urine protein-creatinine ratio, to assess proteinuria.

7. If possible, determinations of serum osmolality and serum osmolar gap.

8. Special diagnostics: intravenous pyelogram (IVP), renal biopsy, and determinations of lead and other heavy metals in the blood as indicated.

Diarrhea, acute-onset

Definition

A definition of acute-onset diarrhea is probably unnecessary; when it happens, you know it! The condition involves a sudden change in bowel pattern, characterized as increased fluidity, frequency, or volume, that is sustained despite empiric or supportive therapy (see also Diarrhea, Chronic). Fundamentally, diarrhea occurs when the amount of water and other intestinal contents reaching the colon exceed the ability of the colon to store the feces and adequately remove the excess water. The pathogenesis of acute diarrhea may be classified as osmotic diarrhea, abnormal gut permeability, secretory diarrhea, or abnormal bowel motility.

In the patient with acute diarrhea, it is conceivable that only one of these mechanisms is involved. However, the longer the underlying cause of the diarrhea persists, the more likely that homeostatic and compensatory mechanisms will be overwhelmed. The pathogenesis of the patient’s diarrhea is then related to a combination of events.

Associated signs

Acute diarrhea is a common presenting sign for which multitudes of diagnostic possibilities exist. The list of associated signs can be, in the clinical setting, extensive. Among the most common signs encountered in an animal presented with acute diarrhea are vomiting, dehydration, slight weight loss, and hematochezia. Abdominal pain, halitosis, flatulence, and borborygmus are other gut-associated signs. However, not all patients with acute diarrhea have primary intestinal disease, such as those with renal or hepatic failure or hypoadrenocorticism; icterus, oral ulcers, muscle weakness, and so on may also be encountered. Fever, anorexia, and lethargy may also accompany acute diarrhea in the dog and cat.

Differential diagnosis

Differential Diagnosis for Acute-Onset Diarrhea

Infectious causes

Intestinal parasites: Nematodes (e.g., ascarids, hookworms, whipworms, Strongyloides, Trichinella); protozoa (e.g., Coccidia, Giardia, Cryptosporidium, Pentatrichomonas)

Bacterial: Escherichia coli, Salmonella, Pseudomonas, Clostridium, Campylobacter, Yersinia enterocolitica, Staphylococcus, Helicobacter (?)

Viral: Paramyxovirus (canine distemper), parvovirus (feline and canine), adenovirus 1; coronavirus and reovirus—minor or insignificant)

Rickettsial: Salmon poisoning

Toxic causes

Antimicrobials or antibiotics, parasiticides, antineoplastic agents, heavy metals, insecticides, organophosphate-containing compounds, antiinflammatory drugs

Dietary causes

Dietary indiscretion, engorgement, food hypersensitivity, sudden change in diet

Bowel obstruction

Foreign body, intussusception, volvulus, neoplasia

Extraintestinal causes *

Renal failure, hepatic disease, hypoadrenocorticism (Addison disease), pancreatitis (acute and chronic)

Idiopathic causes

^* Although characteristically associated with chronic disease, the onset of diarrhea may be acute.

Diagnostic plans

1. History and physical examination, including abdominal palpation. Establish possible exposure to infectious agents and associated signs.

2. Intravenous fluids containing NaCl may be a critical part of the early evaluation (signs associated with hypoadrenocorticism or Addison disease may resolve within minutes to hours) in severely dehydrated patients presented with acute diarrhea.

3. Laboratory profile (to include routine hematology), biochemistry profile (to include amylase or lipase and sodium and potassium), urinalysis, examination of feces (direct and flotation). Perform several examinations before ruling out parasitic disease. Cats should be tested for FeLV and FIV. Dogs should be tested for parvovirus antigen in stool.

4. Abdominal radiographs.

5. Special diagnostic tests as indicated: abdominal ultrasound; endoscopy and mucosal biopsy; stool culture for viruses or bacteria; serologic studies for rickettsial, viral, and fungal disease; and abdominal laparotomy.

Diarrhea, chronic

Definition

Chronic diarrhea is a persistent or gradual change in bowel pattern, characterized by increased fluidity, frequency, or volume of stool, that is sustained for more than 1 to 2 weeks despite empiric or supportive therapy (see also Diarrhea, Acute-Onset). In the clinical setting, the clinical history and associated signs should be used to further characterize chronic diarrhea as large-bowel or small-bowel diarrhea.

Associated signs

Clinical differentiation of small-bowel and large-bowel diarrhea is fundamentally important for the diagnosis and treatment of chronic diarrhea (Table 3-1).

Table 3-1 Clinical Differentiation of Diarrhea of the Small Bowel and Large Bowel

Clinical Signs	Small-Bowel Diarrhea	Large-Bowel Diarrhea
Fecal volume	Markedly increased daily output (large quantity of bulky or watery feces with each defecation)	Normal or slightly increased daily output (small quantities with each defecation)
Frequency of defecation	Normal or slightly increased	Very frequent: 4-10 times per day
Urgency of tenesmus	Rare	Common
Mucus in feces	Rare	Common
Blood in feces	Dark black (digested)	Red (fresh)
Steatorrhea (malassimilation)	May be present	Absent
Weight loss and emaciation	Usual	Rare
Flatulence	May be present	Absent
Vomiting	Occasional	Occasional

Less specific signs associated with chronic diarrheal diseases include dehydration, poor-quality hair coat, and fever. On abdominal palpation, discrete masses, thickened bowel loops, pain, or gas may occasionally be detected. Edema, ascites, and pleural effusion in patients with chronic diarrhea suggest substantial protein losses through the bowel. The patient with pallor should be assessed for intestinal bleeding, as well as for an anemia of chronic inflammatory disease.

Hematologic signs of greatest significance include eosinophilia (allergic or inflammatory) and significant lymphopenia (lymphangiectasia). Hypoproteinemia is associated with extreme malnutrition, protein-losing enteropathies, and enteric blood loss. Hyperglobulinemia is associated with Basenji enteropathy and feline infectious peritonitis (FIP).

Differential diagnosis

Diagnosis of Specific Chronic Diarrheal Disorders

Diarrhea	Diagnostic Test or Procedure
Small-Bowel Type
Exocrine, pancreatic insufficiency	Serum trypsin-like immunoreactivity (TLI)
Chronic inflammatory small bowel disease
Eosinophilic enteritis	Eosinophilia, biopsy
Lymphocytic-plasmacytic enteritis	Biopsy
	Serum protein electrophoresis
Immunoproliferative enteropathy of Basenjis	Radiography, biopsy
Granulomatous enteritis
Lymphangiectasia	Lymphopenia, intestinal biopsy, and total protein and lymphocyte count
Villous atrophy
Gluten enteropathy Idiopathic	Response to gluten-free diet Biopsy
Histoplasmosis	Serology, cytology, biopsy
Lymphosarcoma	Biopsy and cytology
Small intestinal bacterial overgrowth (SIBO)	Culture of intestinal aspirate, folate, response to antibiotics
Giardiasis	Fecal examinations, response to parasiticides
Lactase deficiency	Response to lactose-free diet
Large-Bowel Type
Chronic colitis	Colonoscopy, colon biopsy (multiple samples are required)
Idiopathic Histiocytic Eosinophilic
Whipworm colitis	Fecal flotation, colonoscopy, response to fenbendazole
Protozoan colitis	Saline fecal smears
Amebiasis Balantidiasis Trichomoniasis
Histoplasma colitis	Fecal cytology, colon biopsy, serology, culture
Salmonella colitis	Culture
Campylobacter colitis	Culture
Prototheca colitis	Colon biopsy
Tritrichomonads
Rectocolonic polyps	Digital palpation, barium enema
Colonic adenocarcinoma	Colonoscopy, barium enema, possibly abdominal ultrasound
Colonic lymphosarcoma	Barium enema, colonoscopy
Functional diarrhea (irritable colon)	History, diagnostic workup excludes all other diseases