Adverse Gastrointestinal Food Reactions

Adverse Gastrointestinal Food Reactions (Negative Reactions to Foods that Lead to Stomach or Intestinal Problems)

OVERVIEW

  • The body can react negatively to substances, such as particular foods or ingredients of a food. These negative or “adverse” reactions can be due to true allergic reactions, in which the immune system develops a response to the food (known as “food allergy”). By definition, dietary allergy is an “immunologic” reaction, because the immune system responds to the particular offending substance in the food. Other negative or adverse reactions are not true allergic reactions. The body still reacts to the foods or ingredients of a food, but the immune system in not involved with the abnormal response. When the immune system is not involved, the negative responses are known as “non-immunologic reactions.” These non-immunologic reactions are called “food intolerance”
  • Adverse gastrointestinal food reactions encompass disorders with an immunologic basis (that is, food allergy), non-immunologic basis (that is, food intolerance), and toxic reactions (that is, food poisoning or intoxication)
  • Adverse gastrointestinal food reactions may be associated with vomiting and/or diarrhea in dogs and cats
  • In a practical sense, food allergy and food intolerance may have similar signs, diagnostics, and treatments and may not be easily distinguishable
  • Food allergy is a common cause for signs related to skin problems, such as itchiness (known as “pruritus”), which may be associated with gastrointestinal signs (such as vomiting and/or diarrhea)
  • “Gastro-” refers to the stomach; “intestinal” refers to the intestines
  • “Enteropathy” is the medical term for a disease of the intestinal tract (plural, enteropathies)
  • The small intestines may be described as “small bowel,” as in “small bowel diarrhea”; the large intestines may be described as “large bowel,” as in “large bowel diarrhea”

Genetics

  • Specifics of a genetic basis are not well defined
  • An inherited food allergy has been seen in soft-coated Wheaten terriers
  • Gluten-sensitive enteropathy (specific type of intestinal disease related to the presence of wheat gluten in the diet) has been seen primarily in Irish setters
  • Siamese and Siamese-cross cats may be at increased risk, as compared to other breeds of cats, to develop gastrointestinal food reactions

Signalment/Description of Pet
Species

  • Cats—more common than in dogs

Breed Predilections

  • Inherited food allergy—soft-coated Wheaten terriers
  • Gluten-sensitive enteropathy (specific type of intestinal disease related to the presence of wheat gluten in the diet)—Irish setters
  • Siamese and Siamese-cross cats

Mean Age and Range

  • Any age dog or cat can be affected
  • Irish setters with gluten-sensitive enteropathy—tend to display clinical signs by 4–7 months of age
  • Dogs with long-term (chronic) diet-responsive intestinal diseases (known as “diet-responsive enteropathies”)—generally young adults

Signs/Observed Changes in the Pet

  • Food intolerance commonly produces diarrhea (small or large bowel); vomiting; excessive gas formation in the stomach or intestines (flatulence); decreased appetite (known as “anorexia”); and abdominal discomfort
  • Food allergy is a common cause of skin (dermatologic) changes, such as itchiness (pruritus), which may be associated with gastrointestinal signs (such as vomiting and/or diarrhea)
  • Sudden (acute) food intolerance may accompany feeding a foodstuff to which the pet has never been exposed (known as a “novel foodstuff”; for example, feeding a food that contains “alligator” as an ingredient and the pet has never eaten anything containing alligator), a new food source, or dietary change
  • Clinical signs may cease when the pet is fasted or within days of beginning an elimination dietary trial; an “elimination dietary trial” involves feeding a diet that does not contain substances that the pet normally eats and is free of additives to see if clinical signs improve
  • Physical examination findings are generally non-specific; pet may have abdominal discomfort, excessive gas formation in the stomach or intestines (known as “flatulence”), bloating, or poor body condition

Causes

  • Reactions to food additives, where the individual pet is more likely to develop ill effects (known as “idiosyncratic reactions”)—for example, colorings, preservatives (such as butylated hydroxyanisole [BHA], monosodium glutamate, sodium nitrate, sulfur dioxide); spices; propylene glycol
  • Drug reactions—substances that have an effect on the blood vessels (known as “vasoactive substances,” such as histamine); agents that have an effect on the nervous system to alter mood, anxiety or behavior (known as “psychoactive agents”); stimulants (such as theobromine, caffeine); other drugs
  • Metabolic defects or deficiencies—enzyme defects in the intestinal tract (for example, lactase deficiency leading to lactose intolerance)
  • Toxic reactions to foods or spoiled foods—spices; oxalate toxicity; lectin toxicity; aflatoxicosis (disease caused by eating foods contaminated with aflatoxin, poison produced by certain fungi, including Aspergillus); ergotism (disease caused by eating ergot-contaminated grains or grain products; ergot is a fungus that infects cereal plants); botulism (food poisoning caused by eating food containing botulin, a nerve toxin produced by a particular bacteria); dietary indiscretion, where the pet eats inappropriate things (such as garbage)

Risk Factors

  • Genetic susceptibility suspected in soft-coated Wheaten terriers
  • Young Irish setters susceptible to gluten-sensitive enteropathy (specific type of intestinal disease related to the presence of wheat gluten in the diet) may be at greater risk to develop the disease if exposed to gluten at an early age

Treatment
Health Care

  • Generally treat on an outpatient basis

Activity

  • No restrictions

Diet

  • Feed a novel protein (that is, feeding a protein to which the pet has never been exposed) diet
  • Cats generally are sensitive to more than one dietary ingredient
  • Many high-quality, commercial diets are available for use in dogs and cats
  • If this approach is used, examination of the ingredients of the various diets being fed is recommended to determine if any patterns exist that might help identify the offending ingredient(s)

Medications

  • Generally no medications are used
  • Associated problems (such as antibiotic-responsive diarrhea [ARD] or inflammatory bowel disease [IBD]) may require medical therapy

Follow-Up Care
Patient Monitoring

  • Assess effectiveness of the elimination dietary trial by observing improvement in clinical signs; an “elimination dietary trial” involves feeding a diet that does not contain substances that the pet normally eats and is free of additives to see if clinical signs improve
  • Consider repeating evaluation for primary disease (such as inflammatory bowel disease) if the pet is unresponsive to dietary therapy

Preventions and Avoidance

  • Avoid the offending food ingredient(s)
  • If no specific ingredient has been identified, adhere to a particular exclusion diet (a diet that is designed to eliminate or exclude the food ingredient[s] to which the pet most likely is intolerant)

Possible Complications

  • Antibiotic-responsive diarrhea and inflammatory bowel disease

Expected Course and Prognosis

  • Prognosis for a full recovery is excellent in most affected pets, if dietary recommendations are followed completely
  • Soft-coated Wheaten terriers with food allergy have a guarded prognosis for full recovery

Key Points

  • Feed a diet free of the offending ingredient(s)
  • Do not feed any scraps or vary from the recommended diet
  • Prognosis for a full recovery is excellent in most affected pets, if dietary recommendations are followed completely

Hyperthyroidism

Hyperthyroidism (Excessive Production of Thyroid Hormone)

OVERVIEW

  • Disease condition caused by high levels of thyroid hormones that increase metabolism in the body
  • The thyroid gland normally produces thyroid hormones in response to stimulation by the pituitary gland, the “master gland” of the body; the thyroid hormones normally increase chemical processes occurring within cells of the body; however, in hyperthyroidism, the excessive hormone levels put the cells and body into “overdrive”
  • Thyroid hormones are known as “triiodothyronine” or “T3” and “tetraiodothyronine” or “T4”

Genetics

  • No known genetic predisposition

Signalment/Description of Pet

  • Cats; most common hormonal (endocrine) disease of cats; one of the most common diseases seen in late middle-aged and old cats

Breed Predilections

  • None

Mean Age and Range

  • Mean age in cats, approximately 13 years; range 4–22 years

Signs/Observed Changes in the Pet

  • Involves many organ systems due to the overall increase in metabolism
  • Weight loss
  • Unkempt appearance
  • Poor body condition
  • Increased appetite (known as “polyphagia”)
  • Vomiting
  • Diarrhea
  • Increased thirst (known as “polydipsia”)
  • Rapid breathing (known as “tachypnea”)
  • Difficulty breathing (known as “dyspnea”)
  • Heart murmur; rapid heart rate (known as “tachycardia”); particular abnormal heart beat, known as a “gallop rhythm”
  • Hyperactivity
  • Aggression
  • Large thyroid gland
  • Thickened nails
  • Less than 10% of pets are referred to as “apathetic”; these pets exhibit atypical signs (such as poor appetite, loss of appetite, depression, and weakness)

Causes

  • Cats—autonomously hyperfunctioning thyroid nodules (where the thyroid nodules produce excess thyroid hormones outside of the control of the pituitary gland, so-called “autonomous” production); rarely, thyroid cancer (known as “thyroid carcinoma”)
  • Dogs—thyroid hormone (T4 or T3) secretion by a thyroid cancer (thyroid carcinoma)

Risk Factors

  • Some reports have linked hyperthyroidism in cats to some canned food diets
  • Advancing age increases risk

Treatment
Health Care

  • Outpatient management usually suffices for cats, if drugs that inhibit the production of thyroid hormones (known as “antithyroid drugs”) are used
  • Treatment using a radioactive form of iodine (known as “radioiodine treatment”) or surgical removal of the thyroid gland (known as “thyroidectomy”) require inpatient treatment and monitoring
  • Rare cases of congestive heart failure require emergency, inpatient intensive care

Activity

  • No alterations recommended

Diet

  • Poor absorption of many nutrients and high metabolism suggest the need for a highly digestible diet, with high availability of protein in untreated hyperthyroidism
  • Resolution of signs resulting from excessive levels of thyroid hormones in the body (condition known as “thyrotoxicosis”) eliminates the need for dietary modifications in many pets
  • Dietary modification may be necessary to treat or control complications (such as kidney damage)

Surgery

  • Surgical removal of the thyroid gland (thyroidectomy) is one recommended treatment for hyperthyroidism in cats
  • Surgical treatment of thyroid carcinoma (dogs and cats) is usually not curative, but can control signs (known as “palliative treatment”)

Medications

  • Medications presented in this section are intended to provide general information about possible treatment. The treatment for a particular condition may evolve as medical advances are made; therefore, the medications should not be considered as all inclusive.
  • Radioiodine (radioactive form of iodine) is a safe and effective treatment; use of radioactive iodine requires special facilities; availability of veterinary facilities offering this treatment is limited, but increasing
  • Methimazole (Tapazole) inhibits the production of thyroid hormones (antithyroid drug) and is recommended most often
  • Methimazole can be administered through the skin (transdermally); transdermal methimazole must be prepared by a pharmacist; resolution of signs resulting from the excessive levels of thyroid hormones in the body (thyrotoxicosis) takes longer with transdermal methimazole than with methimazole given by mouth
  • β-blockers—sometimes used to treat some of the heart and nervous system effects of excess thyroid hormones; can be used in combination with methimazole; mainly used to prepare the pet for surgical removal of the thyroid gland (thyroidectomy) or radioiodine therapy; atenolol is useful for controlling rapid heart rate (tachycardia), but addition of an ACE inhibitor is necessary to control high blood pressure (known as “hypertension”) in cats with hyperthyroidism
  • Carbimazole—another useful antithyroid drug that inhibits production of thyroid hormones; not available in the United States
  • Propylthiouracil—is an antithryoid drug that inhibits production of thyroid hormones; it can be useful if methimazole is unavailable; side effects may be more common and more severe than with methimazole
  • Ipodate—a radiographic contrast agent; can be used to treat some cases of mild hyperthyroidism, but not effective in most hyperthyroid pets; long-term effectiveness has not been established

Follow-Up Care
Patient Monitoring

  • Methimazole—physical examination, complete blood count with platelet count, serum biochemical analysis, and serum thyroid hormone (T4) determination every 2–3 weeks for the initial 3 months of treatment; the dosage is adjusted to maintain serum thyroid hormone (T4) concentration in the low-normal range
  • Surgical removal of the thyroid gland (thyroidectomy)—watch for development of low blood-calcium levels (known as “hypocalcemia”) and/or paralysis of the voice box (larynx) during the initial postoperative period; measure serum thyroid hormone (T4) concentrations in the first week of surgery and every 3–6 months thereafter, to check for recurrence
  • Radioiodine (radioactive form of iodine)—measure serum thyroid hormone (T4) concentrations 2 weeks after treatment and every 3–6 months subsequently
  • Kidney function—kidney filtration rates decline following treatment in most affected pets; therefore, perform a physical examination, serum biochemistry, and urinalysis 1 month after treatment and then as indicated by clinical history

Possible Complications

  • Untreated disease can lead to congestive heart failure; diarrhea that is difficult to treat; kidney damage; detachment of the retina (a layer in the back of the eye) as a result of high blood pressure (hypertension); and death
  • Complications of surgical treatment include low levels of parathyroid hormone (known as “hypoparathyroidism”; the parathyroid glands are small glands adjacent to the thyroid gland, which may be removed at the time of the surgical removal of the thyroid gland); low levels of thyroid hormone (known as “hypothyroidism”); and paralysis of the voice box (larynx)
  • Low levels of thyroid hormone (hypothyroidism) is rare following radioiodine therapy (radioactive form of iodine)

Expected Course and Prognosis

  • Uncomplicated disease—prognosis is excellent; recurrence is possible and most commonly is associated with poor owner compliance with medical management; regrowth of overactive thyroid tissue is possible, but uncommon after surgical removal of the thyroid gland (thyroidectomy) or radioiodine treatment (radioactive form of iodine)
  • Reported mean survival time for cats treated with radioiodine is 4 years; mean survival time for cats treated with methimazole is 2 years; mean survival time for cats treated with radioiodine and methimazole is 5.3 years
  • Cats with pre-existing kidney disease have a poorer prognosis; kidney failure is the most common cause of death in hyperthyroid cats
  • Dogs or cats with thyroid cancer (thyroid carcinoma)—prognosis is poor; treatment with radioiodine (radioactive form of iodine), surgery, or both usually is followed by recurrence of disease; chemotherapy is of questionable benefit

Key Points

  • Disease condition caused by high levels of thyroid hormones that increase metabolism in the body
  • Most common hormonal (endocrine) disease of cats; one of the most common diseases seen in late middle-aged and old cats
  • Rare in dogs
  • Potential side effects of drugs that inhibit the production of thyroid hormones (antithyroid drugs) and surgical complications
  • Be aware of possible (rare) recurrence after treatment